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thesis entitled
GIS APPROACH TO EVALUATE A HABITAT SUITABILITY

INDEX (HSI) MODEL (BREEDING SEASON) FOR BALD
EAGLES AROUND TIPPY DAM POND, MANISTEE RIVER, MICHIGAN

presented by

Kobkul Chanchaitong Jones

has been accepted towards fulﬁllment
of the requirements for

M- A. degree in Geographx

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GIS approach to evaluate a Habitat Suitability Index (HSI) model
(Breeding Season) for Bald Eagles

around Tippy Dam Pond, Manistee River, Michigan

By

Kobkul Chanchaitong Jones

A THESIS

Submitted to
Michigan State University
In partial fulﬁllment of the requirements

for the degree of

MASTER OF ARTS

Department of Geography

1 996

ABSTRACT
GIS APPROACH TO EVALUATE A HABITAT SUITABILITY INDEX (HSI)
MODEL (BREEDING SEASON) FOR BALD EAGLES
AROUND TIPPY DAM POND, MANISTEE RIVER, MICHIGAN
By

Kobkul Chanchaitong Jones

This study presents the application of geographic information systems
(GIS) to habitat suitability index (HSI) modeling to assess whether the model can
predict bald eagle reproduction success for the eleven bald eagle nest sites
around the Tippy Darn Pond in Manistee county Michigan. This study applies
the original and a modiﬁed version of the habitat suitability index (HSI) model to
quarter- and half-mile buffer zones around the nest sites. Results from the
analyses indicate that the original HSI model does not relate well to eaglet
production. Two additional variables (Road Length Index, and White Pine Index)
are included in the modiﬁed model.

It is concluded that ﬁxed-diameter buffer zone for all factors are
problematic. The foraging distance limit given in the literature was inappropriate
at this site. A critically important variable, water-based human activities, needs
to be included in the HSI model. The disturbance of breeding bald eagles by
water-based recreation activities appears to be the most important unknown
variable related to the spatial variance of eagle reproduction. Both the original
and the modiﬁed HSI model fail to fully explain the spatial variance of eagle

reproduction. Recommendations for future model enhancements are discussed.

Copyright by
KOBKUL CHANCHAITONG JONES

1 996

To my parents who give me energy and wisdom.

ACKNOWLEDGEMENTS
The creation of any academic work is not a solitary effort, even though there are
times when it feels that way. There are many people who contributed to this
work in direct and indirect ways and to whom I am extremely grateful. First and
foremost is Dr. David Lusch, the chair of my committee, who spent a tremendous
amount of his time in helping, guiding, and teaching me research with critical
reviews of my work. It is Obvious why so many seek Dr. Lusch for intellectual
support and scientific insight. I am deeply indebted to him for all he has done for
me. I would like to thank the other members of my graduate committee: Dr.
Charles Nelson who gave me insight about the recreational aspects of my
research, and Dr. Edward Whitesell who contributed ecology concepts to this

work.

This work would not have be possible without the research facility provided by
the Entomology Spatial Analysis Lab (ESAL). Dr. Stuart Gage who created the
Lab provided me an incredible opportunity to work with and learn from him. Dr.
Gage provided a home for my research. He gave me unlimited use of his lab,
even after I was no longer employed with him. I can not thank him enough for
his generosity. Thanks must also go to Amos Ziegler (also part of ESAL) for his
putting up with my continual technical questions when the computer system or

ARC/INFO did not make sense.

Prior to my starting on this project there were people who set me on the path to
discovery that at the time, seemed unrelated. Dr. Mike Vasievich of the US.
Forest Service (USF S), and Dr. Daniel Stynes from the Department of Park and
Recreation (MSU) gave me my ﬁrst hands on experience into scientiﬁc research.
Jeff Niese, who also worked at the USFS, introduced me to this project.

I met Dr. Richard Stiehl of the National Biological Service (NBS) while I attended
his seminar on Habitat Suitability Index modeling in Colorado. After the seminar
Dr. Stiehl kindly provided advice, over several phone calls, that later followed

during the course of my work.

Thanks to Dennis Hudson who provided guidance in interpreting air photos, a
skill that later became very valuable in the creation of spatial data for my thesis.
Additional thanks to Marcia Larsen, and Donna Paananen at USFS, and Michael
Lipsey at Geography Department (MSU) for their kindness and support. Much

thank to Sharon Ruggles for all her help.

During my thesis work Mr. Rex Ennis, Mr. Chris Schumacher (Manistee National
Forest, Cadillac), Mr. Kevin Stubbs, Mr. Dave Best (US. Fish and Wildlife
Service), Mr. Michael Beaulac, Mr. Tom Wresie, Mr. Sherrnam Hollander
(Department of Natural Resources), Mr. Gary Dawson (Consumers Power
Company), and Mr. Bill Bowerman, all helped me acquire the much needed

existing data for this study.

vi

Special thanks must go to Dr. Karen Klomparens, and the Graduate School for
their help and personal support. I would not have made it through graduate
school without them. Their help is deeply appreciated. Additional thanks to Dr.
Julie VWnkler who gave me the encouragement to start my thesis. Thanks too
must go to Dr. David Homer and Dr. Joe Cousin Of the lntemational Center for

moral support that was given long before this thesis started.

A lasting appreciation goes to Michigan State University which offered me a
great place to learn about school, work, people and myself. The environment at
this university gave me experiences, both good and bad, and opportunities that I

am very grateful for.

Thanks to. Bob and Carol-Lee Jones, my father and mother in law, who gave me
much encouragement and advice. Most importantly, I like to thank my husband
Clint Jones who gave me personal and emotional support and dedicated his time

to me.

vii

TABLE OF CONTENTS

LIST OF FIGURES ....................... xi
LIST OF TABLES . . ..................... xiii

1 INTRODUCTION

1.1 Overview ......................... 1
1.2 Background ....................... 3
1.3 Statement of Problem .................. 6
1.4 Description Of the Study Area ............... 8
1.4.1 Physiography .................... 8
1.4.2 Soil ......................... 11
1.4.3 Vegetation ..................... 11
1.4.4 Climate ....................... 11
1.4.5 Fish ........................ 12

2 THE REVIEW OF LITERATURE

2.1 Habitat Suitability Index (HSI) Models ........... 13
”ﬁg: Bald Eagle Protection ................... 16
"I! 2.3 Bald Eagle Nesting Habitat ................ 18
_... 2.3.1 Food ........................ 19
I,‘ 2.3.2 Cover ....................... 21
I 2.3.3 Nesting Trees vs. Location ............. 22
Ln...“ 2.3.4 Disturbance .................... 25

2.4 Habitat Suitability Index (HSI) Model For

Bald Eagle (Breeding Season) .............. 27

2.5 The Role of Geographic Information Systems (GIS) in

Wildlife Habitat Study ................... 30

3 METHODOLOGY

3.1 Overview ......................... 35
3.2 The Original HSI Model .................. 42
3.3 The Modiﬁed HSI Model ................. 42
3.4 GIS Data Input ...................... 43
3.4.1 Original HSI .................... 44
3.4.1.1 Existing Digital Data ............. 44

3.4.1.2 Creating the Unavailable Digital Data ..... 49

3.4.2 Modiﬁed HSI .................... 56

viii

3.4.2.1 Existing Digital Data ............. 56

3.4.2.2 Creating the Unavailable Digital Data ..... 57
3.5 GIS Data Processing ................... 57
3.5.1 Coverage Preparation ............... 61
3.5.2 Data Analysis ................... 62
3.5.2.1 Original HSI Model .............. 62
SIV2 ...................... 62
SIV3 ...................... 65
SIV4 ...................... 7O
HSI ...................... 71
3.5.2.2 Modiﬁed HSI Model ............. 74
SlV3p and the White Pine Index (WPI) ..... 74
SlV4p and the Road Length Index (RLI) ..... 77
4. RESULTS
4.1 Introduction ....................... 84
4.2 Original Habitat Suitability Index Model (Original HSI) . . . 85
4.2.1 SIV2 ........................ 85
4.2.1.1 Wellston Territory .............. 86
4.2.1.2 Red Bridge South Territory .......... 87
4.2.1.3 Red Bridge North Territory .......... 87
4.2.2 SIV3 ........................ 88
4.2.2.1 Wellston Territory .............. 90
4.2.2.2 Red Bridge South Territory .......... 90
4.2.2.3 Red Bridge North Territory .......... 91
4.2.3 SIV4 ........................ 92
4.2.3.1 Wellston Territory .............. 93
4.2.3.2 Red Bridge South Territory ........... 94
4.2.3.3 Red Bridge North Territory .......... 94
4.2.4 HSI ........................ 95
4.2.4.1 Wellston Territory .............. 95
4.2.4.2 Red Bridge South Territory .......... 96
4.2.4.3 Red Bridge North Territory .......... 96
4.3 Modified Habitat Suitability Index Model (Modiﬁed HSI) . . 97
4.3.1 SlV3p ....................... 97
4.3.1.1 Wellston Territory .............. 98
4.3.1.2 Red Bridge South Territory .......... 98
4.3.1.3 Red Bridge North Territory .......... 99
4.3.2 SlV4p ....................... 100
4.3.2.1 Wellston Territory .............. 101
4.3.2.2 Red Bridge South Territory .......... 101
4.3.2.3 Red Bridge North Territory .......... 102
4.3.3 HSI ........................ 102
4.3.3.1 Wellston Territory ............... 102

4.3.3.2 Red Bridge South Territory .......... 103
4.3.3.3 Red Bridge North Territory .......... 103

5. DISCUSSION

5.1 Introduction ....................... 108
5.2 The Original HSI and the Modiﬁed HSI .......... 110
5.3 General Observation ................... 1 1 1
5.4 The Modified HSI and the Fledging Production ...... 112
5.4.1 Wellston Territory ................. 113
5.4.1.1 The Quarter-Mile Buffer Zone ......... 113

5.4.1.2 The Half-Mile Buffer Zone .......... 115

5.4.2 Red Bridge South Territory ............. 116
5.4.2.1 The Quarter-Mile Buffer Zone ......... 117

5.4.2.2 The Half-Mile Buffer Zone .......... 120

5.4.3 Red Bridge North Territory ............. 121
5.4.3.1 The Quarter-Mile Buffer Zone ......... 121

5.4.3.2 The Half-Mile Buffer Zone .......... 123

6. CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH

6.1 Conclusion ........................ 124
6.2 Suggestions For Future Research ............. 128
APPENDIX
Appendix A
Table 1. Detail results of the original HSI model within the
quarter-mile buffer zone ............... 132
Table 2. Detail results of the original HSI model within the
half-mile buffer zone ................ 134
Table 3. Detail results of the modiﬁed HSI model within the
quarter-mile buffer zone ............... 136
Table 4. Detail results of the modiﬁed HSI model within the
half-mile buffer zone ................ 140

LIST OF REFERENCES ..................... 144

LIST OF FIGURES

FIGURE PAGE

1.1 Study area ........................ 10
2.1 Suitability graph ..................... 28
3.1 Quarter-mile buffer zones around the eagle nest sites

at Tippy Dam Pond .................... 37
3.2 Half-mile buffer zones around the nest sites at

Tippy Dam Pond ..................... 39
3.3 Buffer zone analysis areas ................ 41
3.4 Bathymetry of Tippy Dam Pond .............. 48

3.5 Percent mature trees in the vicinity Of
Tippy Dam Pond ..................... 53

3.6 Housing and camping sites and linear
disturbance features ................... 55

3.7 Supracanopy White Pines within one half-mile Of the

various eagle nests .................... 59
3.8 Model development ﬂowchart ............... 60
3.9 Suitability graph for Morphoedaphic Index (MEI) ...... 66
3.10 Percent mature trees within an example quarter-mile

buffer zone ........................ 68
3.11 Suitability index graph for percent mature trees ...... 72

3.12 Suitability index graph for housing density of
upland evaluation ..................... 73

3.13 White Pine Index (WPI) graph based on the number Of
White Pines ....................... 76

3.15 Cord tangent to a quarter-mile buffer zone ......... 78

vi

3.14 Road Length Index graph based on total road length
within the quarter-mile buffer zone ............ 79

3.16 Road Length Index graph based on total road length
within the half-mile buffer zone ............... 81

4.1 Mean water depth within the quarter-mile and half-mile

buffer-zones ....................... 86
4.3 Percent mature trees within the quarter-mile

buﬁerzone ........................ 89
4.4 Percent mature trees within the half-mile buffer zone. . . . 89

4.5 Housing density within the quarter-mile and half-mile
buffer zone ....................... 92

4.6 Number Of supracanopy White Pine within the
quarter-mile and half-mile buffer zone ............. 97

4.7 Road length within the quarter-mile and half-mile
buffer zones ....................... 100

xii

LIST OF TABLES

TABLE PAGE
3.1 Example mean-depth calculation .............. 63
3.2 Tippy Pond water quality data (1990-1991) ......... 64
3.3 Area and percent of mature trees around nest 1 ....... 69
3.4 Score for each linear feature ................ 80

4.1 Results of the original HSI model within the quarter-mile
buffer zones ........................ 104

4.2 Results of the original HIS model within the half-mile
buffer zones ........................ 105

4.3 Results of the modified HSI model within the quarter-mile
buffer zones ........................ 106

4.3 Results of the modiﬁed HSI model within the half-mile
buffer zones ........................ 107

xiii

CHAPTER 1

INTRODUCTION

1.1 Overview

This study is associated with the Tippy Dam hydroelectric project, which is
owned and operated by Consumers Powers Company (CPCO), under license
from the Federal Energy Regulatory Commission (FERC). The Tippy Dam
Pond, which is about 1,330 acres (538 ha) in size, is situated on the lower
Manistee river and is surrounded by the Manistee National, Forest in Michigan.
The natural setting Of the forested land and the dam pond attracts many ﬁsh,
riparian, and other wildlife species. Bald eagles (Haliaeetus Ieucocephalus), a
state-and federally-listed threatened species, roost, perch, and breed in the

areas around this impoundment.

The hydroelectric impoundment produces an aesthetic resource that has drawn
people to the surrounding river and forest areas for recreation. Today, many
recreational sites and supporting infrastructure have been developed including
parks, campgrounds, boat docks, vacation homes, and businesses. Seasonal

home owners, commuters, and tourists contribute to the economy of the areas.

Because recreation is a major industry in this locale, there is an increasing
demand for developed recreational sites. There are many recreation sites being
proposed for this river/pond system; some of these may adversely affect the
area's threatened bald eagle population. Bowerman and Giesey (1991)
suggested that with any proposed recreational development on the river, the
impact on the existing and potential bald eagle breeding areas should be

analyzed.

The hydroelectric project license requires CPCO, in cooperation with state and
federal resource agencies, to protect, maintain and enhance bald eagle habitats
associated with the project. The federal agencies responsible for managing
these areas must comply with federal environmental protection legislation by
trying to estimate potential impacts of development on the threatened bald
eagles. These agencies must also deﬁne the critical environmental factors
which determine habitat suitability and identify areas where suitable

characteristics may favor both the population maintenance and growth.

The bald eagles and their habitat in the vicinity of Tippy Darn Pond were
selected for this study for three majors ieasons. First, bald eagles are a
threatened species in Michigan which is losing their habitat due to human
activities, land development and urban sprawl. Second, bald eagles around the

Great Lakes have shown a great disparity in reproductive success due to the

effect of chemicals such as DDT in their food web (Bowerman, 1993). Even
though the pesticide DDT was banned more than 25 years ago, these chemicals
still effect bald eagle populations around the Great Lakes area today. More
details about the effects of Chemicals on bald eagle populations can be found in
the studies of Wiemeyer et al. (1984), Gilbertson and Schnider (1991 ), and
Bowerman (1993). The only hope to continue bald eagle populations in
Michigan is to "maintain greater productivity in interior areas to compensate for
lesser fecundity and greater adult mortality along the shorelines of the Great
Lakes" (Bowerman, 1993). Lastly, despite a few bald eagles studies that have
been done in Michigan, none Of these studies have quantiﬁed the bald eagle
habitat values nor analyzed the spatial relationship of bald eagles and human
habitats using geographic information systems (GIS) technology. This study will
introduce this concept of habitat modeling with the assistance of GIS technology

to model bald eagle habitat in this part of Michigan.

1.2 Background

Bald eagle breeding areas in Michigan have been categorized into three groups:
Great Lakes, Interior, and Anadromous. The Great Lakes breeding areas cover
areas within 8 km of Great Lakes shoreline. The Interior breeding areas are
further than 8.0 km from the Great Lakes shoreline. The Anadromous breeding

areas are those Inland breeding areas that are accessible to runs of

Anadromous Great Lakes ﬁsh (Bowerman, 1993). The nesting bald eagles of

this study around the Tippy dam Pond are in the Interior breeding area group.

From 1975 to 1995, there were eleven nest sites that were occupied by three
breeding pairs of bald eagles around the Tippy Dam Pond. Each breeding pair
had their own territory: Wellston, Red Bridge South, and Red Bridge North.
Each territory consisted of a number Of nest sites. Some eagles nested on the
same tree for many years, but others moved around or alternated the use Of

several nest sites.

During the mid-19705, a breeding pair Of eagles moved into the Red Bridge
South territory. This couple occupied the area for twenty-one years and
produced twenty young. Within the twenty-one year period, this pair Of eagles

moved around ﬁve different nest sites.

The Wellston pair moved into the Tippy Dam Pond area in the late 1980s. They
occupied their territory for eight years and produced eleven young while moving

between four nest sites.

The Red Bridge North breeding pair moved into this region in the early 19905.

This pair produced three young in a four year period occupying two nest sites.

TO determine the quality of bald eagle productivity, the average young per
occupied nest is considered. The productivity is considered impaired when the
average young per nest is less than 1.0. To maintain the population stability, an
average of 0.7 young per nest is necessary (Bowerman, 1993). The average
production of the Tippy Dam Pond eagle territories were high to moderate: 1.4
young per year in Wellston; 0.95 young per year in Red Bridge South; and 0.75
young per year in the Red Bridge North territory. The quality of bald eagle

productivity around the Tippy Dam breeding area is still in good condition.

Bald eagles in the landscape around the Tippy Dam Pond produced a promising
average of one young per year. The environmental variables that allow the
species to have good reproductive success in this area need to be assessed
and monitored in order to maintain the future population of the birds. The
environmental factors that shape the suitability Of the habitat for the bald eagle
have not been fully mapped out and quantiﬁed. A study by Bowerman (1991)
evaluated the quantity of bald eagle habitat by visually noting the abundance of
supracanopy White Pines from a light aircraft survey. He also incorporated
aerial photos analysis Of the number Of supracanopy White Pines and human

disturbance features such as dwellings and roads.

Visually interpreting the environmental factors contributing to quality eagle

habitat may not provide sufﬁcient information. Each variable needs to be

mapped out and calculated in some form to give values of the total contribution

from each of the environmental factors in the study area.

Management Of bald eagle habitat within the study area is an important
component of the Manistee National Forest Land and Resource Management
Plan. The managing agencies responsible for this river system desire a method
that can be used to quantify the quality Of the species habitat with which to judge
the effects Of existing conditions and proposed development upon bald eagle.
TO the fullest extent possible, these sites should be managed for both human

recreation and eagle habitat.

1.3 Statement of Problem

This study will employ an existing habitat suitability index (HSI) model for
breeding bald eagles to quantify the quality Of habitat around Tippy Dam Pond.
This particular HSI model has not been evaluated in Michigan since its

development in 1986.

This study will evaluate the original habitat suitability index (HSI) model for the
breeding bald eagle and a modiﬁed version. Results from the original and the
modiﬁed HSI models will be examined to see whether the modiﬁed model can

explain the habit suitability for the bald eagle more accurately than the original

HSI model. The performance of these models will be assessed in light of the
spatial variance of bald eagle reproductive success at the various nest sites. TO
better reﬂect the suitability of the habitat for bald eagles, landscape attributes
from ﬁeld observations related to bald eagle nesting habits will be examined
together with bald eagle reproductive success and the results Of the original and

modiﬁed HSI models.

The following research question will be investigated:

Does the original Habitat Suitability Index model for the breeding bald eagle

adequately explain the spatial variance of nest-speciﬁc reproductive success?

Several subsidiary questions emanated from this principle one:

1. What additional factors which contribute to the quality Of the habitat for bald
eagles can be added to the HSI model to improve its ability to explain
nest-speciﬁc reproductive success ?

2. What scale Of landscape evaluation is most appropriate when assessing
nest-speciﬁc areas regarding habitat quality for breeding bald eagles ?

3. Is it beneﬁcial to implement the HSI model for breeding bald eagles in a GIS

context ?

1.4 Description of the Study Area

The study area is located around the Tippy Dam Pond in the northwestern Lower
Peninsula Of Michigan (Figure 1.1). The three bald eagle territories can be
found on three adjacent USGS 75-minute series topographic quadrangles
(Marilla, Yuma, and Wellston quadrangles). These territories lie within a
bounding rectangle whose corner coordinates (Michigan State Plane, 1927) are:
NW corner ( Marilla quadrangle) - 1,607,823 feet, 362,081 feet

NE corner (Yuma quadrangle) - 1,565,319 feet, 362,081 feet

SE corner (Wellston quadrangle) - 1,607,823 feet, 328,658 feet

SW corner (Wellston quadrangle) - 1,565,319 feet, 328,658 feet

1.4.1 Physiography

The Manistee River basin is located in the northwest part Of Michigan and drains
to Lake Michigan. The glacial history of Michigan formed the topography Of this
areas. The resulting landforms from the glacial deposits include ﬂat to rolling
terrain, with occasional hills ranging from 200 to 400 m in elevation (Federal

Energy Regulatory Commission, 1994).

Figure 1.1. Study area.

 

 

 

Legend / <:
lake I»
township line
twotrack

county road
highway

  
 
    
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11

1.4.2 Soil

Soils of this watershed were developed in a complex set of glacial sediments.
These parent materials, coupled with the various landscape positions, produced
several soil types. The most common characteristics among these soil are that
they are coarse to sandy texture, well- to excessively well-drained, with low

fertility (Federal Energy Regulatory Commission, 1994).

1.4.3 Vegetation

The basic forest cover types in the study area have been extensively modiﬁed
since the later part of the 18005 by forest clearing and residential development.
The current forest cover is second or third growth. Several different vegetation
types are found: Jack Pine, Red Pine, White Pine, and northern hardwoods
including sugar maple, white ash, basswood, hemlock, red maple and red oak
(Federal Energy Regulatory Commission, 1994). One Of the most important

trees to bald eagles is the White Pine because it is used for nesting.

1.4.4 Climate

Michigan is in the mid-latitude portion of North America. The location

determines the amount of seasonal contrast of incoming solar radiation, and the

12

type of upper air Circulation that effects the weather on a day-tO-day basis. The
general climate in Michigan is characterized as temperate with four seasons:
Winter, Spring, Summer, and Fall. However, the Michigan climate is modiﬁed
because it is surrounded by the world's largest bodies of fresh water, the Great
Lakes. The Great Lakes provide a semi-marine type climate to Michigan, even
though this state is located in the mid-continent (Eichenlaub et al., 1990). This
Climate provides an abundance of moisture to the land around the lakes, but the
annual precipitation is moderate compared to other parts of the United States.
Precipitation in the study area shows an annual rainfall that averages 30 inches,
plus 61 inches of snowfall. Snow ground cover averages 4 months or around

120 days per year (Eichenlaub et al., 1990).

1.4.5 Fish

Fish are the most important food source for the bald eagles. The birds around
the Tippy Dam Pond were Observed to feed primarily on benthic-feeding ﬁsh.
Fish species from the Pond that were found in bald eagle nests include Sucker,
Bullhead, Bass, Northern pike, Trout, Panﬁsh, Bowﬁn, an Walleye (Bowerman,

1991).

CHAPTER 2

REVIEW OF LITERATURE

2.1 Habitat Suitability Index (HSI) Models

In the early 19703, American citizens had become increasingly aware that they
were stewards of their natural resources and environment. In response to the
concern of the nation about environmental quality and its increasing interest in
wildlife and wildlife habitat protection, congress passed several laws that
required assessment of environmental conditions and the prediction of future
conditions (Jackson, 1982; Schamberger et al., 1982; Thomas, 1982). These
statues include the Endangered Species Act Of 1973, the National
Environmental Policy Act of 1969, the Federal Water Project Recreation Act, and
the Forest and Range Land Renewable Resource Planning Act of 1974 as

amended by the National Forest Management Act of 1976.

The foundation Of this environmental legislation was the National Environmental
Policy Act (NEPA) of 1969. NEPA is “the culmination of national concern in the
1960’s for natural resource conservation, and public health and welfare
legislation” (US. Fish and Wildlife Service, 1980). NEPA applies to all programs

of all federal agencies and requires these agencies to consider environmental

13

14

values during assessment activities. According to the US. Fish and Wildlife

Service (1980), NEPA stated that all federal agencies shall:
Utilize a systematic, interdisciplinary approach which will insure the
integrated use Of the natural and social sciences and the environmental
design arts in planning and in decision making which may have an impact
on man's environment,

and that they shall

identify and develop methods and procedures, in consultation with the
Council on Environmental Quality. . ., which will insure that presently
unquantiﬁed environment amenities and value may be given appropriate
consideration in decision making along with economic and technical
consideration.

NEPA created a need for a system of habitat evaluation that allows the

assessment of current environmental conditions and the prediction of future

conditions under different management Options. As part of meeting this need,

Habitat Suitability Index (HSI) models were developed.

Numerous HSI models for speciﬁc species have been derived from biological
and habitat information published in the scientiﬁc literature as well as
unpublished information Of ﬁeld experts. These HSI models assign index values
to habitat quality for selected species evaluation. The index ranges from 0.0 to
1.0; 0.0 representing unsuitable habitat, and 1.0 representing Optimum habitat
(US. Fish and Wildlife Service, 1980). This model construction is based on a

logical approach. The ﬁve general steps to approach model construction are:

15

1. Set the model Objectives: The model Objectives develop a framework and a
constraints-set to help guide the model development. They limit the model base
to a geographic area and time period, and set the independent measurement

variable that correlates with the output goal.

2. Identify model components: This step includes the identiﬁcation of potential
variables that can be useful in evaluating habitat suitability for a given species.
The identiﬁcation of model variables for the HSI is based on three criteria:
- Variables should be closely related to the species habitat needs and the
land or water development Changes being studied.

- There should be sufﬁcient information available such that the relationship
between the variables and the Speciﬁc habitat needs of the species can be
described, preferably in a quantitative manner.

- Variables should be practical to measure, estimate, or predict given the
constraints under which the model will be used.

3. Deﬁne model relationships: The relationships between the selected variables
and habitat suitability are explicitly deﬁned in this phase. The important aspect
of this step is to structure the model to deﬁne the rules by which a habitat is to
be evaluated to determine an index of habitat suitability.

l

4. Document the model: The model needs to be documented in order to

promote an understanding of the decision-rationale used during model

construction. By documenting these details, the model is more likely to gain

acceptance.

16

5. Verify and test the model. The HSI model should be veriﬁed prior to its
Operational use. The goal Of the verification should be toward the improvement
of the model to better reﬂect the relationships between the species and its

habitat. (Stiehl, 1995:5-3 to 5-13)

More than two hundred HSI models for ﬁsh and wildlife Species were developed
by the US. Fish and Wildlife Service and published in "Blue Books." Notably,
most of these models have never been fully tested. The need for model
veriﬁcation has been stressed in the literature (Vemer et al., 1986; Morrison et
al., 1992; Duncan et al., 1995), but appropriate data to support veriﬁcation are

frequently lacking (Schamberger and O’Neil, 1986).

2.2 Bald Eagle Protection

Bald eagles were once common birds in the forty-eight contiguous states and
were abundant in Alaska during the early 19003 (King et al., 1972). Human
activities since this time have greatly reduced bald eagle populations. Some
destructive activities have been logging, land clearing, and housing development
which destroy nesting trees and suitable habitat. Later, farmers blamed bald
eagles for killing livestock so the birds were shot. Many bald eagles died from
poisons that were put out by the federal or state pest and predator-control

projects. Bald eagle populations declined relatively slow, but it was ﬁnally

17

recognized and protection laws were considered. In 1940, the Bald Eagle Act
was passed to prevent live or dead bald eagles, their parts, nests, or eggs from

being sold, transported, exported, or imported.

After World War II, DDT and other toxic chemicals were introduced in this
country for insect control. DDT was used widely to control the gypsy moth
during the mid-1950s to 1960s (McCling, 1979). Bald eagle populations
declined drastically during this period. Nobody knew what was causing bald
eagle deaths, but the incidents were brought to the attention of the government
and the National Audubon Society, and intensive action to protect the bald
eagles began. The National Audubon Society’s Continental Bald Eagles Project
was initiated in 1960 with the cooperation Of the US. Forest Service. This
project provided survey and record keeping Of the nesting status of bald eagles
on the various National Forests. Bald eagle nesting status in the Huron-
Manistee National Forests has been recorded ever since (Irvine, 1986). In 1966,
the Department of Interior provided suitable places for bald eagles to nest by
both restricting the use of and Closing access to bald eagle nesting areas on
public land during the breeding season. At the same time, the US. Fish and
Wildlife Service, the US. Forest Service, and US. Bureau of Land Management
(BLM) were required to include protection of bald eagles in their management
plans. In 1967, bald eagles were listed as endangered in the contiguous United

States except in Minnesota, Wisconsin, Michigan, Washington, and Oregon.

18

Michigan banned the use Of DDT in 1970, the ﬁrst state in the nation to do so.
The United States banned the use of poisons, including DDT, on public land in
1972. Since then, eagle populations have grown slowly. The Endangered
Species Act was amended in 1978 to include bald eagles in Minnesota,
Wisconsin, Michigan, Washington, and Oregon on the threatened species list;

bald eagles remain endangered in the rest Of the contiguous states.

Each state also develops its own bald eagle laws in addition to the federal
protection plans. In Michigan, bald eagles are not only protected under the
Federal Endangered Species Act, but also by the Migratory Bird Treaty Act, the
Bald Eagle Protection Act and the Michigan Endangered Species Act. Bald
eagles will also be protected under the Bald Eagle Protection Plan of the
Consumers Power Company around their hydroelectric projects on the Au Sable,

Manistee, and Muskegon river systems in the near future.

2.3 Bald Eagle Nesting Habitat

Quality breeding habitat for bald eagles requires readily available food, shelter,
nest sites, and isolation from human activities. These requirements for bald
eagles nest site selection have been widely observed (Juenemann, 1973;

Grubb, 1976; Andrew and Mosher, 1982; Bowerman, 1993).

19

2.3.1 Food

One of the most important components Of the bald eagle breeding habitat is an
adequate food supply. The availability Of food is strongly associated with the
location of bald eagle nesting sites. In the Greater Yellowstone Ecosystem, bald
eagle breeding area selection is based on a stable food source in the nesting
area (Swanson et al., 1986). In order for bald eagle young to grow and survive,
a constant food supply during the nesting season is critical. Lack of adequate
prey for as little as a few weeks during the breeding season can cause nest

abandonment by adult bald eagles (Hansen, 1987).

Several studies across the United States have indicated that bald eagles that
nest away from coastal shorelines (i.e. interior bald eagles) tend to nest close to
large bodies of water in order to access their favorite food (ﬁsh). The interior
bald eagles were Observed to prey primarily on ﬁsh; 91.1 percent in north-central
Minnesota (Dunstan and Harper, 1975); 77 percent in Maine (Todd et al., 1982),
and 73 percent in Arizona (Haywood and Ohmart, 1986). The same observation
also held true in Michigan. A study by Bowerman in the Upper Peninsula Of
Michigan (1991) demonstrated that ﬁsh comprised the highest percentage of
prey items (81.5 percent). In 1993, Bowerman extended his study to the interior

habitat on the Au Sable, Muskegon, and Manistee rivers in Northern Lower

20

Michigan. Here, 93 percent Of the total Observed prey of the bald eagles was
ﬁsh. The majority of the ﬁsh that are foraged by bald eagles are bottom-feeder
species (generally feed in shallow water) including suckers, bullhead, catﬁsh,

and northern pike.

Although ﬁsh were found to be an important diet for bald eagles, many studies
demonstrated that their diet also included several other food items that have
seasonal importance. Prey species taken by bald eagles in the Greater
Yellowstone Ecosystem varied throughout the breeding season due to changes
in prey availability (Swensen et al., 1986). Bald eagles are also known to be
quite opportunistic and take prey other than ﬁsh if it is readily available
(Mathisen, 1968; Dunstan and Harper, 1975; Todd et al., 1982; Haywood and
Ohmart, 1986). For example, bald eagles consumed winter-starved deer and
road kill during the early nesting season in interior Maine (Todd et al., 1982),
and fed on carcasses Of lambs on San Juan Island, Washington (Retfalvi, 1965).
In another example, Alaskan sub-adult bald eagles used dump sites as an
important food source all year round, and a considerable number Of eagles,
including adults, utilized the dump in winter, especially after snow storms
(Sherrod et al., 1976). Bald eagles have been reported to feed on mammalian,
avian, and reptile species. Bowerman (1991) noticed that the interior bald eagle
in Michigan utilized mammalian and avian prey during the early breeding

season when ﬁsh were less available. He further remarked that along river

21

stretches Of the Au Sable and Manistee river, ﬁsh were not as available and that

the bald eagles that nested there prayed on reptiles.

2.3.2 Cover

Like any other creature, bald eagles need a suitable place to rest. Size and
structure of trees seems to be important aspects to bald eagles when choosing
roosting sites. In Oregon and California, characteristic roost trees are taller and
more open-structured than the surrounding stands with one important attribute--
they were close to the food source (Kiester et al., 1983). Bald eagles also need
shelter, especially in winter. Wintering bald eagles look for places that can
protect them from cold winter wind. Buehler et al. (1991) found that 92.9
percent Of wintering bald eagles selected roosting sites in areas with small
openings adjacent to the roosting trees to avoid prevailing northerly winds. The
protection Of the surrounding trees provides a favorable microclimate for
wintering bald eagles. Consequently, energy expenditures at night are less.
Reduced energy expenditure at night will also reduce food requirements during
the day (Stalmaster, 1981 ). Spending less energy is important when winter food

supplies are limited.

22

2.3.3 Nesting Trees vs. Location

Adult bald eagles tend to use the same breeding area and Often the same nest
each year (Gieck, 1991 ). Bald eagle nests can sometimes be found on cliffs
(Chrest, 1964), and on the ground such as on sea stacks or on hill sides on
treeless islands (Sherrod, 1976). Most Of the time, bald eagle nests are found in
trees, however. Tree species selection for nesting by bald eagles varies
geographically with the forest type of the region. In western Washington, most
nests are found on Douglas-ﬁr and Sitka spruce (Grubb, 1976); but in Marryland
Loblolly pine is preferred (Andrew and Mosher, 1982). In Michigan the

overwhelming favorite nest tree is the White Pine (Bowerman, 1993).

Bald eagles prefer nesting in Old-growth or mature secondary—growth forests.
These old-grth and secondary-grth trees are typically dominant or co-
dominant trees in the forest (Anthony et al., 1982). The height of these
predominant trees has been shown to be a primary factor in eagle nest site
selection (Retfalvi,1965). Juenemann (1973) stated that bald eagle nest trees in
Minnesota were relatively large and prominent with heights ranging from 59 to
112 feet and diameters (d.b.h.) ranging from 20.7 to 37.3 inches. Bald eagles in
the upper Midwest frequently nest on the tallest trees with the greatest d.b.h.;
these range from 73.9 feet to 92.8 feet tall, and from 24.1 inches to 32.9 inches

in diameter (Bowerman, 1993). In Maryland, 70 nesting trees were measured.

23

They averaged 73.6 feet in height and 24.2 inches in diameter ( Andrew and
Mosher, 1982). Finally, the mean height of nine nesting trees on San Juan

Island, Washington was 100 feet (Retfalvi, 1965).

Another important factor for bald eagle nest-site selection is the presence of an
Open forest structure. Typically, bald eagle nesting trees are located in
structurally heterogeneous forests or uneven-aged stands (Grubb, 1976) with
multi-layers that vary considerably in height and diameter (Anthony et al., 1982).
Andrew and Mosher (1982) agreed that open vegetation is an important
Characteristic of bald eagle nesting habitat. In addition to statistical testing, they
found that more than 53 percent of nest sites were associated with some form of
Open vegetation within 100 m of the nest. In Florida, bald eagle nests were built
on dominant trees along ecotones, in Open ﬁelds, and in pastures (McEwan and
Hirth, 1979). In Minnesota (Juenemann, 1973), 80 percent of 25 Observed nest
sites were associated with open land such as sedge meadows, marshes,
plantations, or natural openings. Grubb (1976) found that the majority Of co-
dominant nest trees in western Washington were in heterogeneous stands.
Open forest structure and tall nest trees provide bald eagles with an open view
of the surrounding area (Juenemann, 1973; Grubb, 1976; Retfalvi, 1965) and a

clear ﬂight path for easy access to their nests (Grubb, 1976).

24

The distance from nest to open water is another important attribute for nest-site
selection by bald eagles (Chrest, 1964; Juenemann, 1973; Nye and Suring,
1978 ; Bowerman, 1993 ). Observations of the distance of nests to the nearest
water showed that usually nests were close to Open water. Short distances from
the nest to Open water provide bald eagles easy access to their preferred diet of
ﬁsh. Nest trees in the Columbia river estuary in Oregon and Washington were
located within 1.6 km of the river (Garrett et al., 1993). Taylor and Therres
(1981) found similar results, and did not consider land further than 1.6 km from
water to be suitable nesting habitat in Maryland. From Observing 24 out Of 25
randomly selected bald eagle nest sites in Minnesota, Juennemann (1973)
discovered that those nests were situated less than a half mile from open water.
Bald eagle nest sites were no further than 600 feet in Washington (Grubb,
1976); no further than 240 feet in Alaska (Chrest, 1964), and averaged 312 feet
in the Yellowstone Unit, 639 feet in the Snake Unit, and 1,768 feet in the
Continental Unit of the Greater Yellowstone systems (Swensen et al., 1985). In
1993, Bowerman observed several nest sites in the upper Midwest with distance

to open water ranging from 350 feet to 2,919 feet.

Not only is distance Of bald eagle nest sites to water important but the size Of
the body of water is important also. Nye and Suring (1978) stated that bald
eagles require open water in order to Obtain their major food (ﬁsh). Peterson

(1986) concluded from several studies that the Optimal size Of a lake suitable for

25

bald eagle habitat was one with a surface area greater than 10 square

kilometers (about 2471 acres).

2.3.4 Dlsturbance

Human activities have been Observed to have negative influences on bald
eagles in several regions (Mathisen, 1968; Grubb, 1976; Buehler et al., 1991
Bowerman, 1993; Theres et al., 1993). Retfalvi (1965) stated that human
activities frequently cause reproductive failure in bald eagles. The intensity of
human impact on bald eagles depends on the timing of the activities, the
distance the activities are from the nest, and the view that the eagles have Of the

activities (Therres et al., 1993).

Human disturbance has the most critical impact on bald eagles during times of
egg-laying and incubating (Mathisen, 1968). Chrest (1964) stated that the
highest mortality rate of bald eagles was during the egg stage. During these
periods, the birds have the least tolerance to external disturbances and may
abandon their nests and leave the area. Herrick (1934) believed that bald
eagles did not accidentally break the eggs that were later found in their nests.
Rather, they were likely to destroy their eggs when they were frequently
disturbed by human beings. He furthered suggested that during the incubation

period, human activities should not be present around the nests. As the nesting

26

period advances and the young develop, the same type of disturbance may have
less effect (Mathisen, 1968). In Minnesota, human disturbance during the
incubation period caused bald eagles to abandon their nest (Juenemann, 1973).
Therres et al. (1993) showed a good example of human disturbances from their
study in Chesapeake Bay. Housing development including land clearing, utility
activities, extraction Operations and road construction were responsible for the
decline in available nesting habitat as well as increases in egg and nest-site

abandonment by bald eagles during the breeding season.

Large lakes and rivers attract both bald eagles and people. When people
Choose to live or vacation near open water where bald eagles have chosen to
nest, conﬂicts between these two arise. In north-central Minnesota, bald eagle
nests were found further from shorelines in areas of high development compared
to shorelines without houses (Fraser et al., 1985). In some cases, bald eagles
utilized vegetation as a natural buffer strip against human disturbance
(Juenemann, 1973; Therres et al., 1993). Andrew and Mosher (1982) found that
nest sites located in denser forests with fewer openings that were further away
from water had higher reproduction success rates than nest sites that were
located closer to water with more forest Openings but were also closer to human

activities.

27

2.4 Habitat Suitability Index (HSI) Model For Bald Eagle

(Breeding Season)

The HSI model for bald eagles (breeding season) was created by Allen Peterson
in 1986. This model is designed to be applicable to habitat in North America

located north of the 37th parallel (Peterson, 1986).

Two important elements of HSI models are the environmental variables and the
associated suitability graphs. Each variable is described by a suitability index
estimated from the suitability graphs. The various suitability index values are
used in the HSI equation to calculate a single HSI value. The indexes range
from 0.0 to 1.0; an index value Of 0 for non-suitable habitat, and an index value
of 1.0 for the maximum habitat suitability. For example, from the graph of Figure
2.1, an environmental variable value of 8 would yield an index value Of 0.8. The
HSI is designed to reﬂect the suitability of the habitat in relation to the population

density Of eagles along a shoreline.

Four environmental variables are components Of the HSI model for breeding
season bald eagles: 1) area covered by open water and adjacent wetlands, 2)
Morphoedaphic Index (MEI), 3) the percentage of upland area covered by
mature timber, and 4) the number Of houses and camping sites per unit area

(building density). Collectively, these variables assess the habitat suitability to

28

provide food, shelter, and protection from human disturbance. The HSI equation
uses three indexes to capture these attributes: the suitability Index for Food
(SlF), the Suitability Index for Reproduction (SIR), and the Suitability Index for

Human Disturbance (SIHD).

The suitability Index for Food (SIF) is composed of two variables: 1) area
covered by open water and adjacent wetlands and 2) the Morphoedaphic Index

(MEI).

The area covered by open water and adjacent wetlands is used to produce a
suitability index value, SIV1, which is estimated from the suitability index graph

speciﬁc to this environmental variable.

 

Sultabllity Index (srv1)

 

0 2 4 6 8 10
Area (square kilomlter)

 

 

 

Figure 2.1. Suitability graph.

29

The MEI is measure Of ﬁsh biomass in the water (Peterson, 1986). There is no
existing data that measures the food availability for bald eagles. Since ﬁsh are
the most important food source (discussed previously), MEI was used as an
indirect measure of potential ﬁsh availability. This index is derived from the ratio
of total dissolved solids (ppm) to the average water depth. The MEI variable
generates the second suitable index score (SIV2) from the suitability graph
speciﬁc to the MEI. The Suitability Index for Food (SIF) is equal to the geometric

mean of SIV1 and SIV2:

SIF = (SIV1 x SIV2)"2 ........................... (Eq. 2.1)

The Suitability for Reproduction (SIR) estimated from the percentage Of the
potential nesting area that is covered by mature timber. The percentage of
mature timber produces the third suitability index value (SIV3) which is read from

the graph speciﬁc to this environmental variable.

The Suitability for Human Disturbance (SIHD) is approximated by the number of
housing and camp sites per square kilometer. The fourth and ﬁnal suitability
index value (SIV4) is derived from the housing and camp site density by means

of the built-area suitability index graph.

30

The HSI model for breeding season bald eagles uses the food, reproduction,

and human disturbance factors as shown:

HSI = (SIF) x (SIR x SIHD)"2 ................ (Eq. 2.2)
or, in its final form:

HSI = (SIV1 x SIV2)"2 x (SIV3 x SIV4)"2 .. (Eq. 2.3)

2.5 The Role of Geographic Information Systems (GIS) in Wildlife

Habitat Study

Geographic Information Systems (GIS) technology has obtained recognition as a
set Of powerful tools capable of spatial and temporal analysis with the ability to
perform data base management, graphical display, and model simulation.

The use of this technology has grown rapidly since it beginnings in the early
19805. Over time, this technology has matured through the development Of

numerous, commercially-available GIS software systems.

The use of GIS has emerged as an important addition to the methods used on
the ﬁelds of natural resource and ecological study in recent years. Johnson
(1990) summarized the potential Of GIS in ecological applications. She

explained how others used this technology in natural resource and ecological

31

studies. Examples included analyzing landscape alteration by beaver (Johnston
and Naiman, 1990); conducting vegetation resource inventories (Stefferson,
1987); providing decision support for forest management (Harrington and Koten,
1988); assessing the spatial pattern of landscapes (O’Neill at al., 1988; Pastor
and Broschart, 1990); and estimating cumulative impacts (Johnston at al., 1988).
She pointed out that GIS has been applied to estimating the quality and quantity
Of habitat based on weighted, spatial intersection models (Davis and Delain,
1984; Donovan at al., 1987; Hodgson at al., 1987; 1988; Scapan at al, 1987;
Stanback at al., 1987; Young at al., 1987). Johnson concludes that the
integration of GIS with spatial models, as discussed by Wheeler (1988) and

Burrough at al. (1988), is an enormously promising approach.

Studies that included wildlife habitat assessment as part of ecosystems research
were well suited for GIS application. As habitat modeling was implemented,
however, the limitations of the models become Obvious (Farmer at al., 1982;
Laymon, 1986; Schamberger, 1986). Farmer at. al. (1982) argued that many of
these operational models were constructed from simplistic and aasy—to-maasure
physical and ﬂoristic variables, and they usually lacked a number Of key
variables and appropriate detail. They suggested strategies for improving the

development of habitat models procedures to verify the models.

32

Laymon and Barrett (1986) tested the Habitat Suitability Index (HSI) models
(Created by the US. Fish and Wildlife Service) for three species (spotted owl,
Marten, and Douglas’ squirrel). They applied the HSI models of two species
(spotted owl, and Marten) in site speciﬁc studies, and the Douglas’ squirrel HSI
model to a landscape scale study. Results from the models did not correlate
well with independent measurements which were used for a standard of
comparison for each species. Two main reasons that contributed to these poor
results were that the environmental variables that formed the models did not
contribute enough information to accurately reﬂect the actual habitat quality, and
the habitat data were of questionable quality. They discouraged the use Of

untested models due to the lack of credibility.

Schamberger and O’Neil (1986) suggested that model testing may Obtain mixed
results due to the environmental variables that form the model, and the difﬁculty
of Obtaining an independent measurement. They then provided concepts of

model testing that related to land use applications, and discussed the selection

Of appropriate standards for comparison with the result of the models.

Burlay (1989) described the application of GIS incorporated with habitat
suitability models designed for landscape and wildlife. He explained the
application Of the model to one or more species and gave selection guidance for

choosing GIS software that provides the capability to handle the model.

33

Eng at. al. (1991), and Davis and DeLain (1986) not only utilized a GIS
database for habitat modeling, but also linked the management plan with wildlife
habitat to integrate forest management systems. Eng at. al. (1991) developed
the Habitat Assessment and Planning (HAP) tool, and used GIS to integrate
management plans to HAP. Davis and DeLain (1986) developed and applied a
mathematical habitat suitability index model for spotted owls to two spatial
databases. They linked the habitat suitability, and included habitat suitability
maps to the timber management maps for the impact assessment and timber

production analysis.

Baker and Mangus (1991) developed GIS procedures to analyze sandhill crane
nest sites. They evaluated the HSI model on a-site speciﬁc basis for this specie
for all nest sites and for random sites by creating a buffer zone around each site.
They suggested a GIS analysis of the HSI model by calculating an HSI value for
a wide range of buffer zone width. For example, 50-1000 meter zone at 50

meter intervals.

Pareira at al.(1991) developed a GIS-based habitat model using logistic multiple
regression to assess habitat quality for the Mt. Graham Red Squirrel. They used
a digital map database and GIS to analyze and provide inputs for two logistic
multiple regression models. These models were then used to predict squirrel

presence or absence. Potential habitat losses due to development were

34

assessed using the model. A 3 percent loss Of habitat was predicted. The
authors noted, however, that the important of this estimated impact could not be
determined. Whether a 3 percent habitat loss would cause the extinction Of this

endangered specie or not was uncertain.

Two comments need to be made regarding HSI modeling. First, the HSI model
for the breeding bald eagles has not yet been veriﬁed. Secondly, GIS
technology has not been applied to analyze this specific HSI model.

It also has been recognized that modiﬁcation to the HSI model will be necessary
to ﬁt site speciﬁc areas. Modiﬁcation to the model has not been reported to date

in the literature.

Ecological modeling by its nature has many limitations. These limitations are
from the lack of environmental data which in turn causes the model to be
generalized. For example, in this study the availability of ﬁsh for breeding bald
eagles is not available. Instead, the surrogate variable, MEI was used in place
of the necessary data. These types of linkages make the model less and less
precise. It must be understood that modeling of this type is not a precise
science. Studies of this type are used for investigating and testing to determine
if the model contains the correct factors and whether the factors are weighted

appropriately.

CHAPTER 3

METHODOLOGY

3.1 Overview

This study will apply the original HSI model for Bald Eagles (Peterson, 1986)
and a modiﬁed version of the model on the eleven bald eagle nest sites around
the Tippy Dam Pond. It must be noted that the original breeding season HSI
model for bald eagles (Peterson, 1986) related the index value (0.0 - 1.0) to the
population density of eagles along a shoreline. In this study, the HSI model for
breeding bald eagles is being related to their nest-speciﬁc reproductive
outcomes (i.e. eaglet production). Areas of analysis at each nest site include

both the quarter-mile and half-mile buffer zones (Figure 3.1 and Figure 3.2).

The quarter-mile buffer zone is a circular area with a radius of 1,320 feet
centered on each nest. The half-mile buffer zone includes a doughnut-shaped
area derived from a circular zone with a radius Of 2,640 feet from the nest
excluding the area of the quarter-mile buffer zone as shown in Figure 3.3.

This is to prevent replication of the HSI value for the quarter-mile buffer.

The evaluation within the quarter-mile buffer zone will produce 11 values for the

original HSI model and 11 values for the modiﬁed HSI model.

35

36

Figure 3.1. Quarter-mile buffer zones around the eagle nest sites
at Tippy Dam Pond.

37

 

Legend

county road
power line
twotrack
highway

WI Wellston
N Redbridge South

Redbridge North
lake

 

 

 

 

 

 

 

 

 

 
 
 
    

[/1

 

 

 

 

 

38

Figure 3.2. Half-mile buffer zones around the nest sites
at Tippy Dam Pond.

39

 

Legend

county road
power line
twotrack
highway

 

 
 
 
    

N Wellston
WI Redbridge South
Redbridge North

 

 

 

 

 

 

 

 

 

 

40

‘

Figure 3.3. Buffer zone analysis areas.

41

 

Legend

county road - half mile zone
power line I quarter mile zone
twotrack lake
highway

miles

 

O .25 .5 1

 

 

 

 

42

The evaluation within the half-mile buffer zone results in another 11 values from
the original HSI model and 11 values from the modiﬁed HSI model. Both the
original and the modiﬁed models Of habitat suitability for the breeding bald eagle
were implemented using ARC/INFO version 7.03 on a SUN10 workstation that

operates in SUN OS 413, a UNIX environment.

3.2 The Original HSI Model

The original HSI model that was used in this study consist of variables that were
suggested by Peterson (1986) except for one variable, SIV1. SIV1 is an index
that measures the area covered by open water and adjacent wetlands. This
variable was not included in my study since all eleven bald eagle nest locations
are proximal to the same reservoir. If applied, the SIV1 value will hold constant
in both the original and the modiﬁed HSI models for the 11 nest sites. This study
will use the equation 3.1 listed below. Detail explanation of other variables in

the equation were explained in the Chapter 1.

l
HSI = SIV2 x (SIV3 x SIV4)? .......... (Eq. 3.1 )

3.3 The Modiﬁed HSI Model

The modified model contains all the factors from the original model plus two

additional factors: the White Pine Index (WPI) and the Road Length Index (RLI).

43

The WPI is based on the number Of supracanopy White Pines within the buffer
zones. This index was used to modiﬁed the original SIV3. The new factor,
called SlV3p, is derived from the arithmetic mean Of SIV3 and the WPI as shown

in Eq. 3.2.

SlV3p = (SIV3 + WPI);- .......... (Eq. 3.2 )
The RLI was determined by measuring the length Of the highways, county
roads, two-tracks, and power lines within the buffer zones. This index was used
to modify the original SIV4 to give SlV4p deﬁned as the geometric mean Of SIV4

and the RLl as shown in Eq. 3.3.

I
SlV4p = (SIV4 x RU); ........... (Eq. 3.3)
SO the modified HSI is computed from the following equation:

HSlp is used to represent the modiﬁed HSI.

1
HSlp = SIV2 x (SlV3p x SlV4p)3 .......... (Eq. 3.4 )

3.4 GIS Data Input

The data required for both the original and the modiﬁed Habitat Suitability Index
(HSI) Model for breeding bald eagles were gathered, or generated within a GIS
including both the spatial data (point, line, and area) and their respective

attribute databases.

44

All of the spatial data were referenced to the Michigan State Plane Coordinate
System (1927), central zone with the units in feet. The newly created digital data
were digitized using ARC/INFO version 7.03 and a CALCOMP digitizer. Each

digital ﬁle was cleaned and built to generate topology.

3.4.1 Original HSI

The original HSI required the spatial locations of the nest sites and the three
other variables: SIV2, SIV3, and SIV4. The nest locations, SIV3 and SIV4 were
unavailable as digital spatial data and had to be developed. Digital data
relevant to SIV2 did exist, but were not in the right format for analysis. Several

steps were performed to convert this digital ﬁle to a useable form.

3.4.1.1 Existing Digital Data

The data needed for SIV2 was the average water depth of the Tippy Darn Pond.
SIV2 is a factor scaled by the Morphoedaphic Index (MEI). As described in the
previous Chapter, the MEI is derived from total dissolved solids (ppm) divided by
average water depth (feet). The average water depth within quarter-mile and
half-mile buffer zones for each nest site was calculated using an area weighted

technique which will be discussed in the data analysis section Of this chapter.

45

Water depths Of the whole Tippy Dam Pond were taken from a bathymetry map
that was provided by the Consumers Power Company. It was stored in a CAD

format as an DXF ﬁle in an unknown coordinate system.

The technique that was used to generate a coordinate system and map units for
this CAD ﬁle was to scale and orient the CAD ﬁle to overlay on a reference that

contains a State Plane Coordinate System in unit Of feet.

To generate a usable coordinate system with known map units for this CAD ﬁle,
the Lakes ﬁle for Manistee county, an existing digital ﬁle from the Michigan
Resource lnforrnation System (MIRIS), was used as a reference ﬁle. The Lakes
ﬁle contained all the lakes in Manistee County including Tippy Dam Pond. All

other lakes in the ﬁle were deleted except for Tippy Dam Pond.

lntergraph software was used to visually overlay the CAD ﬁle on the Tippy Darn
Pond vector ﬁle. Before the overlaying, the map units were set to feet and the
CAD ﬁle was converted into an lntergraph format design ﬁle. The bathymetry
map and the reference ﬁle were displayed together on the same computer
screen to show the location of each map. The bathymetry map was interactively
scaled and oriented to match the reference map which was planimetrically
correct and georeferenced to the Michigan State Plane Coordinate System with

units in feet. The newly georeferenced bathymetry map (in lntergraph format)

46

was converted into an ASCII ﬁle using C-MAP software (Center For Remote
Sensing, Michigan State University). The ASCII ﬁle was imported into
ARC/INFO using the GENERATE command to create a bathymetry map

coverage.

The isobaths on the bathymetry coverage used for the analysis were 0, 5, 10,
15, 25, 40, and 50 feet. This coverage was cleaned and built to Obtain a
polygon topology. The area bounded by adjacent contour lines was assigned a

depth attribute derived as follows:

The mean depth of the polygons created from adjacent isobaths was calculated
by adding the value of the two bounding isobaths and dividing by 2. For
example:

Average water depth = 10 +15 = 12.5

 

2

The mean value was assigned, in this example, to the area between the adjacent
10 feet and 15 feet isobaths. These calculated mean values were treated as the
mean depth of each polygon. As a result, the following depths were calculated:
2.5, 7.5, 12.5, 20, 32.5, and 42.5 respectively. The bathymetry map is shown

in Figure 3.4.

47

Figure 3.4. Bathymetry of Tippy Darn Pond.

48

 

 

Legend

Depth (feet)

0 I 20
2.5 I 32.5
I 7.5 I 42.5
I 12.5

 

 

 
  
 
 
   

 

 

 

49

3.4.1.2 Creating the Unavailable Digital Data

The required digital data which were unavailable included the bald eagle nest
locations, the percentage of mature trees, and the location of housing and
camping sites. These data were complied from written reports, aerial photo

interpretation, and USGS topographic maps, respectively.

The US. Fish and Wildlife Service, the US. Forest Service, and the Wildlife
Division, Michigan Department of Natural Resource (MDNR) provided the
information for Bald eagle nest locations and their attributes. This information
was stored in many formats: spreadsheet, reports, and maps. The digital map of
the nest locations was created from bald eagle nests occupied anytime during

the period 1975 to 1995.

Some bald eagle breeding pairs nested on the same tree for many years but
some moved around or alternated the use of several nest sites. The location of
each nest site on the spreadsheet was recorded in Tier, Range, Section, and
subsection, for example 21 N, 13W, 8, NE, SE. These written descriptions were
used to plot locations on the base map (7.5-minute quadrangle, 1224,000 scale).
The nest format does not describe the exact nest site, instead it locates within
quarter-quarter sections (40 acres). Data from reports, and maps were used for

comparison purposes to corroborate the spreadsheet data. Eleven nest

50

locations were digitized using the 40-acre quarter—quarter section centroids to
generate a point coverage. Each nest was stored as a coverage by itself; there

are eleven coverages for the eleven nest sites.

The ﬁrst four nest locations represent the Wellston territory of a single breeding
pair of Bald Eagles. The Red Bridge South territory (a second breeding pair)
contains nest locations 5 to 9. Finally, the last two nests, ten and eleven,
represent the territory of a third eagle pair, the Red Bridge North couple. The
attribute database for each nest site was created using the INFO database

manager.

Mature trees in this study are deﬁned as any tree taller than 20 meters. Percent
of mature trees were derived from visual interpretation of Color Infrared (CIR)
aerial photographs. These aerial photographs from 1978 (scale 1: 24,000) are
the most recent CIR transparencies that are available from the Land and Water
Management Division, MDNR. A one-mile-wide buffer zone was drawn around
the Tippy Dam Pond. Within this analysis area, polygons were drawn on acetate
overlays on the air photos around homogeneous stands that contained the same
amount of mature trees. These cover types were then updated using the most
recent black and white infrared aerial photographs which were taken in 1987 at a

scale of 1:15,840. These two were provided by Land and Water Management

51

Division, MDNR. Percent of mature trees in each polygon was assigned by

visual comparison with a standard crown density scale.

Percent of mature trees in the study area was categorized as 5, 10, 15, 20, 25,
30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90 percent. Areas with
immature trees (less than 20 meter tall), non-forested land, and water were
assigned a value of 0 percent. The polygons of percent mature trees on the
acetate overlays were transferred using a Kargl magnifying rear projector onto a
base map with a scale of 1:24,000 for digitizing. The base map contains objects
such as roads, rivers, and lakes that were used for georeferencing. The

percent mature trees map is shown in Figure 3.5.

USGS topographic maps (1985) at a scale of 1:24,000 were used to generate a
point coverage of houses. These paper maps were referenced to the Michigan
State Plane Coordinate System, during the set-up phase of the digitizing
process. Maps of camping sites were provided by the US. Forest Service,
Manistee National Forest in Cadillac, Michigan (no date). These sites were
transferred using a Kargl magnifying rear projector to the USGS 7.5-minute base
maps (1224,000). These point features were digitized to generate a point
coverage for the camping sites. The map of housing and camping sites is shown

in Figure 3.6.

52

Figure 3.5. Percent mature trees in the vicinity
of Tippy Dam Pond.

53

 

 

33mg 2.35m #mom. .3 :6 $0.22 04 ._._Uu< UmB bozo

 

roomsa

D o- Nix.
I Mm I 8* 1
I E - owes ...W,........,....
I um- 80.x. ,- ,.
I 4230—.

 

 

54

Figure 3.6. Housing and camping sites and
linear disturbance features.

55

 

Legend

 
    
  

county road [:I housing
N power line [3 camping site
twotrack lake

highway

 

 

 

 

 

 

 

 

56

3.4.2 Modiﬁed HSI

Two variables were added to the original HSI to create a modiﬁed HSI. These
variables are the White Pine Index (WPI) which accounts for the number of
supracanopy White Pine trees in the vicinity of the nest site, and the Road
Length Index (RLI) which accounts for the intensity of potential human
disturbances as a function of the total length of transportation corridors in the

vicinity of the nest site.

3.4.2.1 Existing Digital Data

The RLI was based on the total length of highways, county roads, two tracks,
and power lines in the vicinity of the nest sites. These linear features were
stored in digital ﬁles from the Michigan Resource Information System (MIRIS).
All MIRIS data are georeferenced to the Michigan State Plane Coordinate
System (map units in feet). They are stored in lntergraph design ﬁle format.
MIRIS data were created and made available by the Land and Water
Management Division, Michigan Department of Natural Resources (MDNR).
The process of converting these design ﬁles to ARC/INFO coverages was the
same as the process described previously for the bathymetry map. The
highways, county roads, two-tracks, and power lines within the study areas are

depicted in Figure 3.6.

57

3.4.2.2 Creating the Unavailable Digital Data

The WPI is a function of the number of supracanopy White Pine trees proximal
to the nest. The 1985 CIR air photos at a scale of 1:12,000 (provided by the
US. Forest Service, Huron-Manistee National Forest, Michigan) were inspected
in stereo in order to map all of the obvious supracanopy White Pine trees
occurring within a half-mile around each nest location. The supracanopy White
Pines were mapped as individual point features onto an acetate overlays on the
air photos. These points were subsequently transferred using a Kargl projector

. onto a USGS 7.5-minute base map (1:24.000) for digitizing. The supracanopy

White Pine map is shown in Figure 3.7.

3.5 GIS Data Processing

Data processing for both the original HSI and the modiﬁed HSI within the
quarter-mile and half-mile buffer zones were performed using similar
procedures. The general steps in the process are shown in the ﬂowchart

Figure 3.8.

58

Figure 3.7. Supracanopy White Pines within one half-mile

of the various eagle nests.

59

 

 

   
    

Legend

E White Pine

lake

 

 

 

 

 

6O

 

l:> [Identify Potential Environmental Variablg

{l

 

 

 

 

Construct Digital Database
and Attribute Database
Test the Original and
the Modiﬁed HSI Model

 

O

L Compare Results of the Original HSI J
an

 

d the Modiﬁed HSI to Reproductive Success

 

 

 

 

Figure 3.8. Model development ﬂowchart.

61

3.5.1 Coverage Preparation

The GIS input data discussed earlier contained features that covered the whole
landscape around the Tippy Dam Pond. This study evaluated only a portion of
this landscape, focused on the individual nest sites. To be able to perform the
site-speciﬁc studies, all the digital ﬁles needed to be constrained to the quarter-
mile, and half-mile buffer zones of the eleven nest sites. The quarter-mile buffer
zone was created by using a nest location as a center and building a buffer with
a radius of 1,320 ft. around the nest. The half-mile buffer zone used a similar
process but the area of interest in the half-mile buffer zone is the annulus
between the half-mile radius and the quarter-mile radius. To generate an area
with this doughnut shape, the quarter-mile buffer was used to eliminate the

central area in the half-mile buffer using the ERASE command in ARC/INFO.

Following their construction, the quarter-mile and half-mile buffer zones were
used as “cookie cutters” to “clip” all the input digital data (bathymetry, percent
mature trees, number of houses, camping sites, number of white pine, highways,
county roads, two-tracks, and electric lines). The INTERSECT command in
ARC/INFO performs this task. For the purpose of clarity, these nine input ﬁles
within both the quarter-mile and the half-mile buffer zones were uniquely named

for each of the nest sites.

62

3.5.2 Data Analysis

The analysis procedures used for the quarter-mile buffer zones for both the
original and the modiﬁed HSI will be explained in detail. The analysis for the
half-mile buffer zones follow the same procedure. Nest 1 will be used to
demonstrate the analyses, but all eleven nest sites were evaluated using the

same method.

3.5.2.1 Original HSI Model

The food availability factor of the model uses the morphoedaphic index (MEI) as
an estimator of ﬁsh biomass productivity (Peterson, 1986). The MEI is
calculated from the total dissolved solids contents of the water divided by its
mean depth. The mean water depths within the buffer zones for the eleven nest

sites are not equal and must be individually calculated.

An area-weighted mean depth was calculated for each nest site buffer zone in
order to account for the steep bathymetric gradients found in some areas. The
area-weighted mean depth of any of the buffer zones is equal to the sum of

products of each depth polygon area times its mean depth divided by the total

63

area of water within the zone. The calculation is demonstrated by using the

attributes from nest location 1 (Table 3.1) below.

 

Table 3.1. Example mean-depth calculation.

 

 

Area (square feet) mean-depth (feet) area x mean-depth
polygon 1 903371413725 2.5 225842.85
polygon 2 128341837277 2.5 32085458
Total 1 373755.51 343438865

 

The area weighted mean (area x mean-depth)

 

Total area

= 343438865 = 2.5

 

137375551

The area weighted mean of depth of nest 1 = 2.5

Total dissolved solids (TDS) content in Tippy Dam Pond (Table 3.2) was
acquired from the quarterly water quality sampling conducted by Consumers
Power Company from June to February during 1990 - 1991 (Environmental

report p. E2-5).

64

 

Table 3.2. Tippy Pond water quality data (1990 - 1991).

 

June September November February

 

Total dissolved solids (ppm) 192 184 138 246

 

The average value of 190 was used for this study since it is close to the TDS

value in June (192) which is the only month sampled during the breeding season

(March - July).

The measurement of MEI can be done by using the total dissolved solids (TDS)

in relation to water mean depth of the lake as following:

MEI = total dissolved solids (ppm) ..... Eq. 3.5

 

water mean depth (feet)

For this example, the MEI 190 = 76

2.5

MEI of nest 1 = 76

 

Tne MEI o
habitat su

given by

s_njs_

SIV3, the
percent

mature t

To den

weights

Figure :
around
ll'tESe p

Table 3

 

 

65

The MEI of nest 1 (76) is related to an SIV2 value of 0.96. The food factor of
habitat suitability (SIV2) is positively related to the MEI via a curvilinear function

given by Peterson (1986) and shown in Figure 3.9.

SIV3, the suitability index for bald eagle reproduction, is estimated by the
percent of potential nesting area cover which is measured by the percent of

mature trees in each nest’s buffer zones.

To derive an average percent of mature trees for each nest site, an area

weighted mean technique was used.

Figure 3.10 shows the polygons of percent mature trees within one-quarter mile
around nest 1. Table 3.3 shows the area and percent mature trees for each of
these polygons. The area weighted mean is calculated and shown below

Table 3.3.

 

66

 

         
      

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100

Morphoedaphic Index
Figure 3.9. Suitability graph for Morphoedaphic Index (MEI).

 

67

Figure 3.10. Percent mature trees within an
example quarter-mile buffer zone.

68

 

 

. Bare land

w ., 45 percent
I 50 percent
I 55 percent
I 60 percent
I 70 percent

 

Legend

W] half mile zone
N quarter mile zone

lake

miles

 

O .25

 

 

 

69

 

Table 3.3. Area and percentage of mature trees around nest 1.

 

 

 

Record Area(square feet) Percent percent x area

1 662862.68 45 298288206

2 176341253 70 1234388771

3 178000.09 45 801000405

4 756321.81 50 378160905

5 294089.58 0 0

6 61424.31 55 337833705

7 356140.70 60 2136844200

Total 4072251 .7 223840571 .3
Weighted area mean for nest 1 = 2238405713 (square feet x percent)

 

4072251] (square feet)

= 54.96 percent
Note that the area covered by water is not considered for this calculation
because the potential nesting area does not include the water. Only the percent

of mature trees in the land area was considered.

SIV3 is linearly related to the percent of mature trees as shown in Figure 3.11.

70

The value of weighted percent mature trees of nest location 1 = 54.85. This

value gave the value for SIV3 for nest location 1 = .72.

M

The suitability index for human disturbance is estimated from an inverse, linear
function housing density. The housing density in this study is deﬁned as number

of houses and camping sites divided by total land area within the study zone.

Number of houses and camping sites ,for example nest location 1 is equal to the
number of records from the clipped housing coverage plus the number of record

from the clipped campsite coverage:

Number of record in Housing1 = 9

Number of record in Camping-site1 = 0
So, there are 9 houses, and 0 camping sites in the quarter-mile buffer zone of
nest 1. The total number of human disturbance points is equal to number of

records in Housing1 added to the number of records in the Camping1 coverage.

Number of disturbance locations = 9 + 0 = 9

71

The total land area of nest location 1 is obtained from the Mature-trees1
coverage.

Total land area = 4072251] square feet = 0.38 square kilometers

Housing density for nest location 1 Number of human disturbance points

 

Total land area (square kilometer)

24

The housing density value (24) is plotted on the suitability graph of human

disturbance (Figure 3.12) to produce an SIV4 of 0.

H I

The three required variables for the original HSI model for nest sites are:

SIV2 = .96
SIV3 = .72
SIV4 = 0

1
From Eq. 3.1 the original HSI = SIV2 x (SIV3 x SIV4)3

Nest1 HSI value = .96 x (.72 x 0)"? = o

n

 

      

  
 
 
 
   

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Figure 3.11. Suitability Index graph for percent mature trees.

73

 

  
     
     
     
 

   

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Figure 3.12. Suitability index graph for housing density of upland evaluation.

QL

74

3.5.2.2 Modiﬁed model

SIV3 and the White Pine Index Pl

SlV3p is a modiﬁcation of the variable SIV3 which uses the WPI as shown in

Eq. 3.2. The potential area for nesting habitat around the Tippy Darn Pond was
assessed by the percent mature trees (SIV3) within the buffer zone. But the
majority of bald eagles in Michigan utilize White Pine for their nesting trees
(Bowerman, 1991). Therefore, supracanopy White Pine trees should be used as
another component of SIV3 to identify the potential nesting habitat for the bald

eagle.

The WPI is based on the number of supracanopy White Pines in the buffer zone.
The number of supracanopy White Pines in each buffer was calculated by
counting the number of records in each point coverage, Whitepine1 to
Whitepine11. Each of these coverage has a point attribute table (PAT) and the
number of records in each PAT can be found by using the ARC/INFO command

SELECT < tables name> in TABLES.

The number of supracanopy White Pines in each buffer zone is listed in
Appendix A, Table 3 and Table 4. The highest number of White Pine in a

quarter-mile buffer zone was 106 on nest 6. This number was used as the

75

maximum number of white pine that result in a WPI value of .05 in the suitability
graph. The highest value of the White Pine Index was set to .05 in order to add
sensitivity to the presence of supracanopy White Pines into the percent mature
trees factor (SIV3) without overly bias this factors. According to Bowerman
(1991) “ a potential breeding area includes 1 or more areas of 50.6 ha (125
acres) or greater located near forest or riparian edges, with at least 8
supracanopy White Pines of a 60.96 cm (24 inch) diameter at breast height
(DBH) minimum”, was suggested by the Hiawatha National Forest (1986).
With this suggestion the lowest number of supracanopy White Pines was set to
8. Sites containing eight or fewer supracanopy White Pines are assigned a WPI
value of 0.01. Since the nesting tree is a point feature within a landscape
habitat which is assessed by SIV3, allowing the additive WPI to spatially vary
between 1 percent and 5 percent seem appropriate at this time. The White

Pine Suitability Index is shown in Figure 3.13.

The quarter-mile buffer zone around nest site 1 contain 86 supracanopy White
Pines. Using the relationship shows in Figure 3.11 the derived value of the
White Pine Index for this site is .042. SlV3p is calculated from Eq. 3.2 as
shown below:

SlV3p (.72 + .042)"2

= 0.87

76

 

mmmm

 

 

 

 

Figure 3.13. White Pine Index (WPI) graph based on the number of
White Pines.

77

SIVQQ and the Road Length Index (RLI)

There are many types of human disturbance, for example, water-based
activities such as boating, canoeing, and ﬁshing or land-based activities
associated with dwelling sites, hiking, skiing, and hunting. Logging operation,
extractive sites, oil gas exploratory production sites, and trafﬁc along roads also
disturb eagles. Human disturbance in the original HSI was only accounted for
by housing density. The Road Length Index (RLI) was added in this study to
compensate for several linear disturbance features. The RLI accounts for the
total length of highways, county roads, two-track, and power lines in each buffer
zone. The water—based and other activities mentioned above were not included

because data about the use were not available.

The road length index suitability graph was created by using the minimum and
maximum line length within a buffer zone. The maximum road length for the
quarter-mile buffer is the diameter of the quarter-mile buffer zone which is 2,640
feet and is set to a RLI of 0.1. The minimum line length is 0, of course, and
yields a RLI of 1. The line lengths are negatively related with the Road Length

Index; the longer the summed lengths the lower the RLI.

The RLI was not set to 0 when the line lengths equal or exceed the maximum;

instead the lowest RLI was set to 0.1 because its multiplicative against SIV4. lf

8C

de

78

RH was allowed to go to zero, it could completely null out the spatial variance of
SIV4. It was decided that linear disturbance features should be able to lower
SIV4 by no more than 90 percent (i.e. RLI = 0.1). The suitability graph of the

Road Length is shown in Figure 3.14.

The RLI suitability graph for the half-mile buffer zone was created in the similar
fashion. The only different was that the maximum value of the line length is
equal to the cord of the circular doughnut shape in the half-mile zone as
demonstrated in Figure 3.15.

Figure 3.15. Cord tangent to a quarter-mile buffer zone.

‘r

Cord = 2 (R2 - :3)“ (Eq. 3.6)
R '2 radius of the half-mile buffer zone ( 2640 feet)

r = radius of the quarter-mile buffer zone (1320 feet)

Cord = 2 (6969600 - 1742400)"2 = 4573 feet

79

 

 

Road length (feet)

 

 

 

Figure 3.14. Road Length Index graph based on total road length
within the quarter-mile buffer zone.

80

Therefore, the upper threshold value for the line length in the half-mile buffer
zone = 4,573 feet which is assigned a value of the RLI = 0.1. The minimum of
line disturbance length remains 0 which is set to a value of RLI 1. Figure 3.16.

shows the suitability graph of RLI for the half-mile buffer zones.

To ﬁnd the overall value of RLI for a buffer zone, the length of each linear
disturbance feature was measured and multiplied times its weighting factor.
The summed score of all the linear features was compared with the appropriate
RLI suitability graph to derive the RLI value. The RLI feature weights are as

follow (Table 3.4).

 

Table 3.4. Score for each linear feature.

 

feature weight
highways x 1.6
county roads x 1.4
two-tracks x 1.2

power lines x 1.0

 

81

 

   
  
  

          
      
      

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Figure 3.16. Road Length Index graph based on total road length

within the half-mile buffer zone.

82

The weight for each line type was multiplied by its summed length in the buffer
zone. The total weighted line length for all road types and power lines were
added up to provide the total score of the linear features.

Total weighted line length = [(power line length) + (two-track length x 1.2) +

(county road length x 1.4) + (highway length x 1.6)] Eq. 3.7

The lengths of the linear features in each digital ﬁle, Highway1 to Highway11,
Cnty-road1 to Cnty-road11, Twotrack1 to Twotrack11, and Powerline1 to

Powerline11, are stored in the arc attribute tables (AAT). The example below
demonstrates how to calculate the total weighted score of each linear feature

and the total weighted lengths of all the linear features around nest 1 to derive

the RLI.
Highway1.AAT
Total length of Highway1 = 2145.776 feet
Score = 1.6
Total score of Highway1 = 3433.24
Cnty-road1.AAT
Total length of Cnty-road1 = 0 feet
Score = 1.4
Total score of Cnty-road1 = 0

83

Twotrack1 .AAT

Total length of Twotrack1 = 2192.53 feet

Score = 1.2

Total score of Twotrack1 = 2631.03
Powerline1 .AAT

Total length of Powerline1 = 0

Score = 1

Total score of Powerline1 = 0

Total score of the linear features = 3433.24 + 0 + 2631.03 + 0 = 6064.27
The total score of the linear features is greater than 2640 feet which equates on
in the suitability graph to an RLI = 0.1. This value is used in Eq. 3.3

SlV4p = (SIV4 x RLI)":

SlV4p = (0x0.1)"2 = o

In summary, the modiﬁed HSI model for nest site 1 = SIV2 x (SIV3p x SIV4p)"2
= 0.96 x (0.87 x 0)”
= 0

In this case, the impact of the zero value from SIV4 is obvious.

CHAPTER 4

RESULTS

4.1 Introduction

The evaluation results of the original and the modiﬁed HSI of the eleven nest
sites within the quarter-mile and the half-mile buffer zone will be presented.

Charts and Tables will be used to visualize the results of all nest sites.

Explanation of the results will be based on the three bald eagle territories which
subdivide the study area: Wellston, Red Bridge North, and Red Bridge South.
Each territory was occupied by a nesting pair of eagles. Usually, several nests
can be located in one territory and the eagle pair may occupy or build a different
nest from one year to the next. These nests were use by the eagles over the

period from 1975 to 1995.

The Wellston territory consists of nests 1, 2, 3, and 4. The second territory, Red

Bridge South, comprises nests 5, 6, 7, 8, and 9. The last two nests, 10 and 11,

make up the Red Bridge North territory.

84

 

85

4.2 Original Habitat Suitability Index Model (Original HSI)

The results of the original HSI model in the quarter-mile and the half-mile buffer
zones, and the bald eagle reproductive outcomes are shown in Table 4.1 and

Table 4.2, respectively, at the end of this chapter.

4.2.1 SIV2

The area-weighted average water depth around each nest determined the
values of SlV2. Figure 4.1 shows the average water depth within the quarter-
mile and half-mile buffer zones. More detail can be found in Appendix A, Table

1 and Table 2.

86

 

 

 

 

 

so
\.
xx
xx
A ‘\\x\
\\ xx
xx xx
xx xx
101 xx xx
xx xx
xx xx
xx xx
5* xx xxxx
xxx . xxxx
1234567891011
nest sites Iquarter mile half mlle

 

 

 

 

 

 

Figure 4.1. Mean water depth within the quarter-mile and half-mile
buffer zones.

4.2.1.1 Wellston Territory

Nest 1 and nest 2 are located by shallow water (less than 5 feet deep) within the
quarter-mile and the half-mile buffer zone. As shown in Appendix A, Table 1
and Table 2, the shallow water proximal to nest 1 and nest 2 in the quarter-mile
zone gave high SIV2 values of 0.96 for both nest sites. The SIV2 values of nest

1 and nest 2 in the half-mile zone were 0.96 and 0.85, respectively.

The same eagles also occupied nest 3 and nest 4, however, where the deepest

water was located (deeper than 25 feet). The average water depth around these

87

two nests yielded very low values of SIV2; 0.35 and 0.33 in the quarter-mile,

and 0.34, and 0.32 in the half-mile buffer zone, respectively.

4.2.1.2 Red Bridge South Territory

Three nests ( 5, 6 and 7) were located next to shallow water (less than 5 feet
deep). The average water depth of nests 5, 6, and 7 yield very high SIV2 values
of 0.94 in the quarter-mile buffer zone and 0.94, 0.91, and 0.93 in the half-mile

zone.

The last two nests in this territory , 8 and 9, were located adjacent to rather deep
water (deeper than 15 feet). The SIV2 was as low as 0.45 for both nests in the

quarter-mile buffer zone , and 0.40 for both nests in the half—mile buffer zone.

4.2.1.3 Red Bridge North Territory

This territory contains nests 10 and 11. These two nests were located near
moderately shallow water (less than 10 feet) in the quarter-mile and the half-mile
buffer zone. The SIV2 values yielded from these water depths were 0 .77 in the

quarter-mile, and 0.88 in the half-mile for both nests.

88

4.2.2 SIV3

The percentage of mature trees in the immediate area provides the value of
SIV3. Figures 4.3 and 4.4 present the percentage of mature trees within the

quarter-mile and the half-mile buffer zone, respectively.

The majority of mature trees in the quarter-mile buffer zone fell within the 51 - 75
percent range except for nest 1 and nest 2. Nests 1 and 2 contained mixed
areas of tree growth where the percentage of mature trees ranged from 0 to 75

percent (see ﬁgure 4.3).

The percentage of mature trees in the half-mile buffer zone was somewhat
different and can be put into 3 groups. The ﬁrst group, nests 1 to 4, contains a
mixed range of mature trees from 1-25 %, 26-50 %, 51-75%, and >75%. The
percentage of mature trees in the second group, nest 5 to nest 9, were in 51- 75
range. The last group, nests 10 and 11, are dominated by well-stocked, mature

forests (percent mature trees mostly 51-77% or higher than 75 percent).

89

 

 

 

nest sites

 

 

Figure 4.3. Percent mature trees within the quarter-mile
buffer zone.

 

 

 

«:8:

10 11

nest site

 

 

Figure 4.4. Percent mature trees within the half-mile

buffer zone.

90

The weighted area of percent mature trees that was used to calculated the
percent mature trees and the area of each group is shown in Appendix A, Table

1 for the quarter-mile and Table 2 for the half-mile buffer zone.
4.2.2.1 Wellston Territory

The weighted areas of percent mature trees in the quarter-mile buffer zone were
not homogeneous, 54.89%, 48.67%, 65.56% , and 68.5% around nests 1, 2, 3,
and 4, respectively. As a result, the SIV3 ﬁgures were 0.72, 0.65, 0.86, and 0.91

for the corresponding nest sites.

In the half-mile buffer zone, the weighted areas of percent mature trees also
showed a similar pattern. The weighted areas of percent mature trees were
49.4%, 49.14%, 67.9%, and 61.22% for nests 1, 2, 3, and 4, and yielded SIV3

values of 0.66, 0.66, 0.91, and 0.81, respectively.

4.2.2.2 Red Bridge South Territory

The quarter-mile buffer zone produced quite homogeneous values for the
weighted areas of percent mature trees in this territory: 68.28%, 69.36%,

65.97%, 60.55%, and 60.44%. The consequence of these percentages yielded

 

91

SIV3 values of 0.91, 0.92, 0.86, 0.8, and 0.8 to the corresponding nest sites (5,

6, 7, 8, and 9).

The weighted areas of percent mature trees of nests 5, 6, 7, 8, and 9 in the half-
mile buffer were 62.5%, 67.95%, 66.95%, 56.51%, and 56.32%. The SIV3

figures were 0.83, 0.91, 0.9, 0.75, and 0.75 corresponding to each nest site.

4.2.2.3 Red Bridge North Territory

In the quarter-mile buffer zone, the SIV3 of nests 10 and 11, 0.88 and 0.86,
were produced by the weighted area of percent mature trees of 66% and

64.48%, respectively.

The half-mile buffer zone consists of higher values for the weighted area of
percent mature trees (71% and 71.79%) than the quarter-mile buffer zone. The
corresponding values of SIV3 for nests 10 and 11 were also higher (0.94, and

0.96).

92

4.2.3 SIV4

Housing density, the total number of houses and the number of camping sites
per square kilometer, were used to estimate the SIV4 within the quarter-mile and
the half-mile buffer zones. Figure 4.5 shows the housing density around each
nest site within the quarter-mile and the half-mile buffer zone. Appendix A,
Table 1 and Table 2 show the actual number of housing and camping sites

around each buffer zone.

 

 

8 61‘ B 8
: i 1

housing denslty (building/ka)
0|

 

 

 

 

 

 

 

 

1 2 3 4 5 6 7 8 9 1O 11

 

"‘“m Iquartern'ile Elhdfm’le

 

 

 

 

 

 

Figure 4.5. Housing density within the quarter-mile and half-mile
buﬁerzones.

93

4.2.3.1 Wellston Territory

Notice in the quarter-mile buffer zone that the only nest that contained zero
housing and camping sites was nest 4. Since there was no housing or camping
site disturbance, the highest value of SIV4, 1.0, was produced.

For all the nests in this territory, nests 1 and 2 were the only two nesting areas
that contained only houses; there were no camping sites around these two
nests. Nest 1 was in a more populated area, having 9 houses, while the area
surrounding nest 2 contained 2 homes. So, houses were the only component
that accounted for the zero value of SIV4 for nest 1, and 0.75 for nest 2.
Campsites were the only component that was responsible for the SIV4 of 0 for

nest 3.

In the half-mile buffer zone, nests 1 and 2 were the only two nests that had
houses and no camping sites. The number of houses around nest 1, and nest 2
were 7 and 14, respectively. The SIV4 values of 0.75, and 0.45 were produced,
respectively, for the houses around the two nests. The area around nest 3
contained 9 camping sites but no houses. The SIV4 for nest 3 was 0.55. The
only nest in this territory that was disturbed by both housing and camping sites
(7 and 3, respectively) was nest 4. These housing and camping sites brought

the value of the SIV4 down to 0.3.

94

4.2.3.2 Red Bridge South Territory

There were no housing sites in the quarter-mile buffer zones around any of the
nest sites in this territory. Camping sites were the only component that
accounted for the value of SIV4. Nest 5 had no camping sites nearby so the
SIV4 was equal to 1.0. Nests 6 and 7, each contained 1 camping site that
yielded the SIV4 value of 0.85 and 0.8, respectively. The quarter-mile buffers
around the last two nests, 8 and 9, contained 4 camping sites each. These nests

received SIV4 values of 0.25 and 0.2, respectively.

There was no housing sites within the half-mile buffer zones of any nest site
within this territory. All ﬁve nest sites (5, 6, 7, 8, and 9) were within a half-mile of
camping sites ( 5, 7, 9, 12, and 12 , respectively), yielding corresponding SIV4

values of 0.8, 0.7, 0.6, 0.45, and 0.4.

4.2.3.3 Red Bridge North Territory

Both nests in this territory (10 and 11) had quarter-mile buffer zones that
contained of camping sites, (4 and 5, respectively) yielding SIV4 values of 0.35

and 0.15.

95

Nests 10 and 11 in the half-mile buffer zone had no housing disturbance.
However, twelve camping sites were located around nest 10 and eleven
campsites were nearby nest 11 producing SIV4 values of 0.5 and 0.55,

respectively.

4.2.4 HSI

4.2.4.1 Wellston Territory

HSI values in the quarter-mile buffer zone were 0.0 for nests 1 and 3. Nests

2 and 4 produced HSI values of 0.67 and 0.315, respectively.

In the half-mile buffer zone, the HSI value of the four nests were varied. The
highest HSI value of the four nests was 0.675 from nest 1. Nest 2 produced a
moderate HSI value of 0.463. The HSI values of 0.24, and 0.158 were produced

by nests 3 and 4, respectively.

4.2.4.2

Nesls !
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4.2.4.2 Red Bridge South Territory

Nests 5, 6, and 7 in the quarter-mile buffer zone produced rather high HSI
values of 0.897, 0.832, and 0.78, respectively. The last two nests in this

territory, 8 and 9, yielded quite low HSI values of 0.201 and 0.18, respectively.

In the half-mile buffer zones, nests 5, 6, and 7, produced rather high HSI values
of 0.766, 0.726, and 0.683, respectively. An HSI value of 0.232 was produced

by nest 8, and 0.219 by nest 9.

4.2.4.3 Red Bridge North Territory

In the quarter-mile buffer zones, the HSI values of the two nests were moderate
to low. An HSI value of 0.427 was produced from nest 10, and a value of 0.277
from nest 11. The HSI value from the half-mile zone for nest 10 and nest 11 are

quite similar; 0.548 and 0.581.

97

4.3 Modiﬁed Habitat Suitability Index Model (Modiﬁed HSI)

Results of the modified HSI model in the quarter-mile and the half-mile buffer
zone including the bald eagle reproduction outcome are shown in Tables 4.3

and 4.4 respectively, at the end of this chapter.

4.3.1 SIV3p

The number of supracanopy white pines around each nest was used to estimate
the SIV3p factor. The spatial variance of white pines in the vicinity of each nest
will be examined using Figure 4.6. The values of SIV3p will be explained using

Table 3 and Table 4 in Appendix A.

 

 

 

 

 

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N
0
5
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nest sites

 

a quarter mile I half mile

 

 

 

 

 

Figure 4.6. Number of supracanopy White Pine within the quarter-mile
and half-mile buffer zones.

98

4.3.1.1 Wellston Territory

In the quarter-mile zones, nests 1 and 2 contain signiﬁcantly more white pines
than nests 3 and 4 (see figure 4.6). Nest site 3 has the fewest supracanopy
white pines of any of the eleven nest locations. All of the sites have well over
the minimum suggested number of white pines (eight).The results of the SlV3p
calculations for all the nests in the quarter-mile zone were high. Nests 1, 2, 3,

and 4 generated SlV3p values of 0.87, 0.83, 0.94, and 0.97, respectively.

A similar pattern exist among the half-mile zones: the number of white pines for
nest 1 and nest 2 is greater than that for nest 3 and nest 4. The disparity in
numbers of white pines between nests 1 and 2 and nest 3 and 4 is much less
within the half-mile buffer zones. The half-mile SlV3p values for all the nests

were high: nest 1 = 0.84, nest 2 = 0.84, nest 3 = 0.97, and nest 4 = 0.91.

4.3.1.2 Red Bridge South Territory

Supracanopy white pines in the quarter-mile buffer zones of nests 5, 7, 8, and 9
are nearly the same. Nest 6, on the other hand, had a signiﬁcantly higher
number of white pines. In fact, this location had the greatest concentration of

white pines within the quarter-mile buffer of any of the eleven sites. The SlV3p

99

values for all the nests were high; 0.97, 0.98, 0.94, 0.91, and 0.91 for nests 5, 6,

7, 8, and 9, respectively.

The half-mile buffer zones of, nests 5, 6, and 7 contain high to extremely high
numbers of white pines, with the highest in the vicinity of nest 7. The lowest
number of white pines appear around nests 8 and 9. The values of the SlV3p in
nests 5, 6 and 7 (0:94, 0.98, 0.97) were higher than nests 8 and 9 (0.88 and

0.88).

4.3.1.3 Red Bridge North Territory

White pines for nest 10 and nest 11 were similar to one another in both the
quarter-mile and the half-mile zones. The quarter-mile values of the SlV3p were
0.95 and 0.94. The proximity of these two nests accounts for their similarity. In
the half-mile zones the SlV3p values were very high (nest 10 = 0.99, nest 11 =

1.0).

 

100

4.3.2 SlV4p

SIV4p values were the result of modifying the SIV4 factor of the original HSI
model with the Road Length Index (RLI) as described in the methodology.
Figure 4.7 explains the absolute road length. The details of RLI are portrayed in

Tables 3 and 4 in Appendix A.

 

 

18000-

16000 --

d

«3mm

 

 

 

 

 

 

 

 

 

 

 

7 8 9 10 11

I quarter zone
I3 half zone

 

 

 

 

 

 

 

 

Figure 4.7. Road length within the quarter-mile and half-mile buffer
zones.

101

4.3.2.1 Wellston Territory

In the quarter mile zones, nests 1 and 2 showed high disturbance from linear,
cultural features (road length greater than 4,000 feet). On the other hand, there
was no linear disturbance nearby nest 3 and nest 4. The RLI of nests 1, 2, 3,

and 4 were 0.1, 0.1, 1.0 and 1.0, respectively.

The linear, cultural disturbance in the half-mile zones of nest 1, nest 2, and nest
4 was very high (greater than 12,000 feet). Nest 3 also showed a high value of
road length (greater than 5,000 feet). Since the linear disturbance was so high,

a low RLl value of 0.1 was determined for all nest sites.

4.3.2.2 Red Bridge South Territory

Linear disturbances in the quarter-mile zones of this territory were very low.
Nests 7, 8, and 9 showed no linear disturbance features at all. These three
nests were assigned the highest value of RLI = 1.0. There were small
disturbances (less than 500 feet) in the quarter-mile zones of nest 5 and nest 6.

The RLI around these two nests was, therefore, moderately high (0.79 and 0.8).

102

In the half-mile buffer zones, all the linear disturbances were somewhat high and
distributed quite equally among all the nest sites. The RLI of 0.26, 0.19, 0.325,

0.17, and 0.22 were assigned to nests 5, 6, 7, 8, and 9, respectively.

4.3.2.3 Red Bridge North Territory

Nests 10 and 11 are proximal to high linear disturbances in the quarter-mile
zones. The RLI for both nest sites was accordingly very low (0.1). The
disturbance in the half-mile buffer zones for these two nests was also very high,

yielding a minimum value of RLI = 0.1 for both nest sites.

4.3.3 HSI

Results of the modiﬁed HSI model in the quarter-mile and the half-mile buffer

zones are shown in Tables 4.3 and 4.4.

4.3.3.1 Wellston Territory

The HSI values of nest 1 and nest 3 were 0 in the quarter-mile zone. Nest 2 and

nest 3 produced moderate HSI values of 0.459 and 0.325, respectively.

103

In the half-mile buffer zones, HSI values of 0.459 and 0.358 were produced for
nest 1 and nest 2. Nests 3 and 4 produced lower HSI values of 0.162, and

0.1 27, respectively.

4.3.3.2 Red Bridge South Territory

In the quarter-mile zones, nests 5, 6, and 7 produced high HSI values of 0.872,
0.847 and 0.862 respectively. The HSI values of nest 8 and nest 9 were lower
(0.304 and 0.288) than the other three nests in this territory. Following a similar
pattern, in the half-mile buffer zones, the HSI values of nests 5, 6, and 7 were
moderate (0.614, 0.54, and 0.61) while the HSI values of nest 8 and nest 9 were

low (0.197 and 0.204, respectively).

4.3.3.3 Red Bridge North Territory

Nest 10 and nest 11 in the quarter-mile zones produced HSI values of 0.325 and
0.262, respectively. In the half-mile zones, HSI values of 0.377 was produced

from nest 10, and 0.388 from nest 11.

104

 

 

 

 

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CHAPTER 5

DISCUSSION

5.1 Introduction

The original HSI model was designed to apply to a broad area across the
country. It was not designed to ﬁt problems in a speciﬁc area. In detailed site
speciﬁc analysis, problems and associated factors can better be identiﬁed. To
accommodate this need, the original model needs to be modiﬁed to handle

speciﬁc problems in particular areas.

There are two drawbacks to the original HSI model. The ﬁrst is human
disturbance factor. Housing density is the only variable that accounts for this
disturbance factor in the original model. In addition, the suitability graph for
housing density is too general. It assumes that all the buildings (housing and
camping sites) have the same intensity of disturbance to nesting eagles. This
assumption may not be accurate. The type of activity and distance of the activity
from the bald eagles had a big role to play in how disturbing the activity was to
the bald eagles. Bowerman (1991) observed bald eagles behavior response to
different type of human activities, and stated that ground-related human
activities had the most impact follow by water and air borne activities. Distance

determine the level of response to the activity by the bald eagles. As an

108

109

example, human activities within 500 meter caused a 75 percent alert response
in bald eagles (Bowerman, 1991). The suitability graph should be ﬁne tuned to
represent the intensity of common activities around each type of building
structure. This study did not modify the suitability graph for housing density

because no disturbance intensity data were available.

Other types of human disturbance are not addressed in the original HSI model.
Road activities are not accounted for nor is disturbance due to power lines. The
power lines themselves are not particularly detrimental to eagles. Rather, the
use of power line clearance zone by humans (hiking, ORV, trafﬁc, etc.) can be
disturbing to nesting eagles. Both the disturbances from road or trail use and
power lines clearance use are assigned quantiﬁed values of disturbance
magnitude in the modiﬁed HSI model. Water-based human disturbances
(swimming, fishing, and boating, etc.) were not accounted for in the original or

the modiﬁed models.

Secondly, the suitability factor for bald eagle reproduction does not include an
inventory of speciﬁc nesting trees (supracanopy White Pines in the Tippy Dam

Pond landscape) except for the percentage of mature trees.

110

5.2 The Original HSI and the Modiﬁed HSI

The modiﬁed HSI model shows some improvements over the original HSI model.

One obvious improvement is in the human disturbance factor. The changes to

this factor allows the modiﬁed HSI model to assess the linear disturbance

(highway, county roads, two tracks, and power lines) in the quarter-mile and half-

mile buffer zones around each nest. The disturbance intensity of each linear

type was also identiﬁed by assigning different scoring to each linear feature. I
The improvement of the human disturbance factor can be demonstrated by an

example from nest 2.

The original HSI value of nest 2 (Table 4.1) was 0.67 with a housing disturbance
(SIV4) score of 0.75. The addition of the linear disturbance score (RLI = 0.1) to
the housing disturbance score (0.75), provided a new human disturbance
(SlV4p)score of 0.27 (Table 4.3). With the SlV4p, the modified HSI produced a
score of 0.459. The human disturbance score was adjusted by the RLI. Roads

activities had shown a negative influence on the nesting bald eagle at nest 2.

Another improvement was the addition of the White Pine Index (WPI) to the
suitability for reproduction index (SIV3). In Michigan, the majority of bald eagles
nest on supracanopy White Pines (Bowerman 1993). Clusters of White Pines

were observed from air photos interpretation around all nest sites. White Pines

111

should be another key variable to indicate the habitat suitability for bald eagle
reproduction. Since all nest sites consisted of clusters of White Pines, the

adjusted original SlV3p was higher than the original SIV3 for all nest sites.

The modiﬁed HSI model appears to be more accurate in modeling the breeding
bald eagle habitat than the original HSI model. Therefore, all of the following

discussion will be speciﬁc to the modiﬁed HSI model.

 

5.3 General Observation

The value of SIV2 (determined by average water depth) varies across the
landscape from nest 1 to nest 11. The implication of these values suggests that
bald eagle nest locations were not based on the average water depth across the

Tippy Dam Pond.

This can be demonstrated by the average water depth of each nest in the three
territories (Appendix A, Table 1, and Table 3). In the Wellston territory, nest 1
and nest 2 were located adjacent to very shallow water, around 2.5 feet, while
nest 3 and 4 are proximal to the deepest water (greater than 25 feet). The Red
Bridge South territory contains five nests. The ﬁrst three sites (5,6,7) are located
along shallow water (less than 3 feet deep), while the other two nests (8,9) are

next to deeper water (greater than 17 feet). Finally, in the Red Bridge North

112

territory, the two nest sites (10, 11) are located along moderately shallow water

(around 6 feet).

Even though the average water depth of all nest sites varied, each territory had
at least one neighborhood that contained shallow water. As an example,
although the average water depth of nest sites 10 and 11 (Red Bridge North
territory) was moderate, these nests were close (about half mile) to the
shallowest part of the Tippy Dam Pond. Thus shallow water areas were part of

all nesting territories.

5.4 The Modiﬁed HSI and the Fledgling Production

Bald eagle reproduction is the only available independent measurement for this
study. The reproduction success of each nest site for each territory will be
compared with the HSI scores. The comparisons will also examine the
landscape attributes around the nest and the territory. The discussion will be
based on the results of Table 4.3 and Table 4.4, and APPENDIX A Table 3 and
Table 4. The discussion will focus on the quarter-mile buffer zone since it is an

exclusive zone for bald eagle management plans.

5.4.1 1

A pair
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113

5.4.1 Wellston Territory

A pair of breeding eagles started utilizing the area during the 19803. This
territory was occupied for 8 years, and a total of 11 young were produced. Nest
4 was the most productive and was occupied the longest (5 years), with an

average production of 1.4 young per year.

Nest 1, 2, and 3, each were occupied for only 1 year. Nest 2 and 3 produced a
rather high yearly average number of two ﬂedglings per year. Nest site 1
produced no young. However, from a wildlife biologist perspective (Ennis pers.
comm), a one-year occupancy is not sufﬁcient for determining the relationship of

the nest site and the habitat suitability around the nest.

5.4.1.1 The Quarter-Mile Buffer zone

The HSI values for the quarter-mile buffer zone for each nest site were different
except for nests 1 and 3. These nests generated HSI scores of 0 while nests 2

and 4 produced HSI scores of 0.459, and 0.325 respectively.

The HSI scores of nests 1 and 3 were inﬂuenced by the SIV4 value. The

housing around nest 1 was the only factor that gave the SIV4 value of 0 while

 

114

the density of camping sites determined the SIV4 value of 0 for nest 3 (Table 3,

Appendix A).

It is not appropriate to say that these two nests contained 0 or no habitat suitable
for nesting eagles. As mentioned earlier in the discussion of the drawbacks of
the suitability graph for housing disturbance, the intensity of the activity around
different building structures is not accounted for. The suitability graph for
housing density assumes that all building structures produce the same amount
of disturbance intensity. The HSI scores of nest 1 and nest 3 show the
consequences of that assumption. Since these two nests were occupied for only
1 year in different time periods, there was not enough information to justify the 0

values of the HSI.

In looking at nest 2 and nest 4, it can be seen that the HSI score of nest 2 was
higher (0.459) than nest 4 (0.325). While both sites had high reproduction
success (2 young per year for nest 2 and 1.4 young per year for nest 2), nest 4
was occupied for a longer period of time (5 years) compared to nest 2 (1 year).
This raises the question of why nest 4 produced a lower HSI value than nest 2.
Since nest 4 was located near deeper water than nest 2, the SIV2 for nest 4
would be lower (0.33) than the SIV2 for nest 2 (0.96). The contribution of the

average water depth to the HSI model results in the lower HSI value of nest 4.

115

Further investigation was carried out to determine whether the SIV2 (determined
by the average water depth) around each nest provided enough information to
judge the food supply for each nest. Wildlife biologist Rex Ennis, at the Huron-
Manistee National Forest, observed that bald eagles in Wellston territory
foraged around the delta where the Pine River enters the Tippy Dam pond. This
delta is located in the vicinity of the quarter-mile buffer zone of nest 1 and nest

2. The average water depth of nests 1 and 2 is shallow (2.5 feet) which

 

produced an SIV2 value of 0.96. From ﬁeld observations, the food source for
the eagles occupying nest 4 was provided by the areas around nest 1 and nest 2
(which have a high value of SIV2 of 0.96). Accordingly, the HSI value of nest 4
should be recalculated by substituting the SIV2 value of nest 4 (0.33) with the

SIV2 of nest 2 (0.96). The adjusted HSI value of nest 4 should be:

HSlp = (SIV3p x SIV4p)“2 x SIV2 = (0.97 x 1 )"2 x (0.96) = 0.945

The SIV2 value calculated within a quarter-mile radius of a nest site did not

adequately assess the actual food supply for each nest site.

5.4.1.2 The Half-Mile Buffer Zone

Looking beyond the quarter-mile to the half-mile buffer zone around nest 4, there

was high disturbance potential from housing and camping sites, and from linear

116

disturbance features that brought the HSI value in the half-mile zone down to
0.381 by the calculation below (note: SIV2 = 0.96 will be used for the same

reason give above)

HSIp = (0.91x 0.173) "2 x 0.96 = 0.381

The intensity of human impact on bald eagles depends on the timing of the
activities, the distance the activities are from the nest, and the visual view that
eagles have of the activities (Therres et al., 1993). Bald eagles seem to avoid
areas of high human disturbance. On occasions, when the disturbances around
the nests were high, bald eagles utilized vegetation as a buffer to avoid viewing
human activities (Juenemann, 1973; Therres et al., 1993). This may explain the

situation of bald eagles utilizing nest 4 in the Wellston territory.

5.4.2 Red Bridge South Territory

Nesting eagles have occupied this territory for 21 years and produced 20 young.
Overall ﬁve different locations have been used for nesting. Two nests (6 and 7)
were occupied for only one year. Nest 5 was utilized for the greatest number of
years, (10 years), though not continuously for this period of time. The birds
moved among three nest sites (5, 6, and 7), starting with nest 5 for two years,

then to nest 6 for 1 year, back to nest 5 for 7 years, then to nest 7 for 1 year.

They m

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117

They moved to other nests (8,9) for 5 years and then back to nest 5 for one

year

This nesting pair of eagles seems to favor nest 5. The reasons that the Red
Bridge South pair moved around the area are uncertain. However, some
activities around the site may explain their behavior. Nest 5, 6, and 7 are
located near the boat launch (west bank, immediately downstream from Red
Bridge). Boats traveling downstream from the boat launch Nests (moving toward
Tippy Dam Pond) enter the Red Bridge South territory. As a result, recreation
activities such as boating and ﬁshing may occur very close to these nest sites.
These human activities may have disturbed the nesting birds causing them to
move around the area in subsequent years in an attempt to ﬁnd a peaceful nest

site.

5.4.2.1 The Quarter-Mile Buffer Zone

Nests 5, 6, and 7 are located very close to each other. The reluctance of the
birds to move away from these sites entirely, could indicate that the area
provides good environmental factors for nesting and foraging despite the human
disturbances. In the quarter-mile buffer zone, the HSI values for nests 5, 6, and

7 were high (0.872, 0.847, and 0.862) as expected. The suitability index for

It

118

reproduction (SlV3p) was 0.97, 0.98, and 0.94 for nest 5, nest 6, and nest 7,

respectively.

There was no housing and very few camping sites in the area: 0 for nest 5, and
only 1 for nest 6 and nest 7. So building disturbance was low and thus yielded
high SIV4p values (1, 0.85, and 0.8). The linear disturbance potential from
roads and power lines was also low. Together, these environmental factors

provided high HSI values for nests 5, 6, and 7.

f

Nest 5 produced the highest HSI value (0.872) of all the nest sites around the
Tippy Dam Pond. The reproduction average of nest 5 over the 10 years it has
been occupied, however, was only 0.4 young per year. Nest 6, which was
occupied for only one year, had no production. Nest 7, which was also occupied

for only 1 year produced one eaglet.

It is necessary to examine why the rate of bald eagle reproduction from these
three nests was low when their HSI values were so high. The suitability index
for reproduction (SIV3p) was high, and the land-based human disturbances were
low which yields high SIV4p values. It is important to note, however, that neither
the original HSI model nor the modiﬁed HSI model accounted for water-based
human disturbances (the intensity of boating, canoeing, swimming, and ﬁshing

activities). If included in the analysis, water-based human disturbances would

Uﬂl

the

Ir:

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119

undoubtedly lower the HSI values of nests 5, 6, and 7. Lower HSI values for

these sites would agree more favorably with the eagle reproduction data.

Ironically, the HSI values of nests 8 and 9 were lower than the three previous
nests, but the productivity was higher. Nest 8 was occupied for 6 years and

produced 9 young; an average production of 1.5 young per year. The eagles
occupied nest 9 for 3 years producing 6 young, an average of 2 offspring per

year. Two factors could be responsible for these results.

Nests 8 and 9 are located adjacent to moderately shallow water. The problems
of the SIV4 factor (human disturbance) were from the suitability graph discussed
earlier (place-based rather than activity-intensity—based). The average water
depth of these two sites was moderate, resulting in an SIV2 value of 0.45 for
both nests. There were no data existing on the foraging habitat of this breeding
pair. No reason to believe that they would not forage as far away from their nest
as the breeding pair at nest 4 did. Under these conditions an adjustment of the
suitability index may be appropriate. An adjustment of the suitability index for
food (SIV2) can be substituted in a similar manner to that of the Wellston
territory. If the SIV2 values of nests 8 and 9 are replaced by the SIV2 value of

0.94 from the three other nests (5, 6, and 7), the new HSI would be:

HSlp for nest 8 (SIV3p x SIV4p)"2 x SIV2

(0.91x0.5)"2x0.94 = 0.634

 

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120

HSlp for nest 9 (0.91 x 0.447)"2 x 0.94

0.60

These adjusted HSI values for nests 8 and 9 (0.634 vs. 0.304; 0.60 vs. 0.288,
respectively) are more in concert with the reproduction data, but in comparison
with similar relationships from nest 4 (adjusted HSlp = 0.945 vs. average
reproduction of 1.4 young per year) these indicate that the amount of

unexplained variance is still some what high.

5.4.2.2 The Half-Mile Buffer Zone

The results of the HSI and the factors that control it within the half-mile buffer
zones are very similar to those from the quarter-mile zones. The half-mile HSI
scores of all nest sites were lower: than the quarter-mile HSI scores due to the
larger linear disturbances from two-tracks and the increase point disturbances
from camping sites. This spatial relationship suggests two things. First, suitable
eagle breeding habitat in the Tippy Dam Pond area is very insular. Much of the
landscape is fragmented or disturbed. Second, the spatial density of two tracks
and camping areas, or at least the timing of their use, is a problem that can be

mitigated by management planning.

fl

5.4.3 F

Breedir
occupi
nest t

ahdt

5.4..

121

5.4.3 Red Bridge North Territory

Breeding eagles moved into this territory in the early 19905. It has been
occupied for 4 years and 3 young were produced . This pair of eagles occupied
nest 10 for 1 year and produced no young. They have used nest 11 for 3 years

and have produced 3 young at this site.

5.4.3.1 The Quarter-Mile Buffer Zone

In the quarter-mile buffer zone, the HSI values of these two nests are low: 0.325
for nest 10 and 0.262 for nest 11. Camping sites were the only point disturbance
that inﬂuenced the value of the SIV4. Linear disturbances of these two sites
were due to two-tracks. The disturbance of two-tracks reached the maximum-

value threshold and pulled the value of the RLI down to its minimum (i.e. 0.1).

Two variables for these sites could be adjusted based on ﬁeld observations and
the assumption: the linear disturbance factor and the SIV2 (food/foraging factor).-
Around the two nest sites, the RLI was inﬂuenced by the presence of two tracks.
However, the two—track on the east side of the Pond were closed to the public
during the breeding season (Ennis pers. comm.) but it is not certain if two-tracks
within the quarter-miles zone at the west side of the Pond were closed to public

during the breeding season (Schumacher pers. comm.) The total length of two

Ir!

track
t265
only

total

The
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SOL

mill

122

track at the west side was measured to be 879.38 feet long around nest 10, and
1265.69 feet around nest 11. If the disturbance on the west side of the river is
only considered, the RLI values of nests 10 and 11 that were measured from the

total two-track length would be around 0.71, and 0.57 respectively.

The foraging habitat data of the Red Bridge North territory did not exist. The
same assumption about the foraging area previously applied to the Red Bridge
South territory could apply to this area. Nest 10 and 11 were located about half
mile away from the shallow water where nest 5 was located. So the SIV2 of nest
5 (a Red Bridge South Territory site) could be used to substitute for the SIV2 of
nests 10 and 11. The adjusted HSI values of nests 10 and 11 after modifying

the SIV2 and the RLI can be seen below:

RLI = 0.71 for nest 10
RLI = 0.57 for nest 11

SIV2 = 0.94 for both nest sites (10, 11)

Nest 10 SIV4p = (SIV4 x RLI)"2
SIV4p = (0.35 x 0.71) "2 = 0.498

HSlp = (SIV4p x SIV3p)"2 x SIV2

(0.498 x 0.95) "2 x 0.94

= .647

123

Nest 11 SIV4p = (0.15 x 0.57)"2 = 0.292

HSlp (0.292 x .94)"2 x 0.94

0.492

5.4.3.2 The Half-Mile Buffer Zone

The HSI values in the half-mile buffer zone of nest 10 and 11 are a little bit
higher then the HSI in the quarter-mile zone (0.377 vs. 0.325 and 0.388 vs.
0.262 for nest 10 and 11, respectively) from three reasons: SIV3p, SIV4p and
SIV2. The half-mile buffer zone comprised a little bit higher values of SlV3p
(0.99 and 1 for nest 10 and 11), and SIV2 of 0.8 for both nests. The housing
disturbance in the half-mile zones were a little bit lower than the quarter-mile .
zones but the linear disturbance remained the same. Thus, the values of SIV4p
for nest 10 and 11 in the half-mile buffer zone (0.22 and 0.23 respectively) were
a little bit higher than the values of SIV4p in the quarter-mile buffer zone (0.187
and 0.122 for nest 10 and 11 respectively). Notice that human disturbance
factors were controlled by camping sites and two-tracks. The same discussion
of the half-mile buffer zone of Red Bridge South can also be applied in the Red

Bridge North territory.

CHAPTER 6

CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH

6.1 Conclusions

The central focus of this thesis was the adequacy of the original HSI model for
the breeding bald eagle to explain spatial variance of nest-speciﬁc reproductive
success. The original HSI model is not sufﬁcient to evaluate the habitat
suitability for the bald eagle around the Tippy Dam Pond. Many human
disturbance activities around the landscape were not accounted for by the
original HSI model. The human disturbance factor of the model only addressed
point disturbances: housing and camping sites. In addition to the lack of
variables that explain the human disturbance component, the suitability graph
that was used to measure the suitability index for the housing and camping sites
assumed that these two features generated the same intensity of disturbance to
bald eagles. The suitability index for food, represented by factor SIV2 was not
sufﬁcient to measure the food supply of the bald eagles. There were not enough
data about available food sources around the Tippy Dam Pond to adequately
adjust the SIV2. As an example, nest site 4 has a very low SIV2 factor score,
but in reality the eagle occupants of this site forage several miles away in an

area with an outstanding SIV2 characteristic.

124

The

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not

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125

The ﬁrst subsidiary question of the thesis was what additional factors that
contribute to the quality of the habitat for bald eagle might be added to the HSI
model to improve its ability to explain nest-speciﬁc reproductive success.

The modiﬁed model was created to adjust the HSI values to account for some of
the missing attributes in the original model. It was obvious that the human
disturbance factors of the HSI model needed to be reﬁned. The land-based
activities that were included in the modiﬁed HSI model cover human
disturbances associated with housing and camping sites, various classes of
roads and trails, and power line clearances. It was not feasible for this study to
identify the disturbance intensity from either. housing or camping sites. The
suitability graph of the building disturbance from the original HSI model was
used in the modified HSI model. The intensity of linear disturbance from
highways, county roads, two tracks, and power lines were weighted by
multiplying an assumed, relative value of disturbance magnitude to each linear
feature type. The values of the magnitude that were assigned to these various
linear disturbance features were estimated from ﬁeld observations made by

Bowerman (1991 ).

Even though the modiﬁed HSI model has two additional variables, it does not
adequately predict the habitat suitability for the nesting bald eagles as measured
by their reproductive success. Suggested additional habitat details that are

needed to more completely deﬁne the model will be reviewed in the next section.

 

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126

The second subsidiary research question dealt with the appropriate scale of
landscape evaluation when assessing nest-speciﬁc areas regarding habitat
quality for breeding bald eagles. As shown in the differences in factor scores
between the quarter-mile and the half-mile buffer zones, suitable bald eagle
habitat in the Tippy Dam area is very insular and the landscape is highly
fragmented in terms of disturbance and resources. The two ﬁxed—distance buffer
zones that were used for all factors were not adequate to explain how bald
eagles use their habitat. The food factor that was calculated within the buffer
zones was totally wrong since many of the birds foraged outside these buffer

zones.

The third and ﬁnal subsidiary question is the beneﬁt of implementing HSI model
in a GIS. ARC/INFO provides the Arc Macro Language (AML) to collect all the
necessary commands to process the analysis for the HSI model. Using macros
in a GIS allows the analysis to be quickly modiﬁed. This saves a great deal of
time over manual operation methods and makes it possible to conduct iterative
trials, or “what if' scenario investigations. This approach is critical to support the

need to modify the HSI model to account for site-speciﬁc conditions.

GIS did provide the ability to easily calculate and analyze the HSI values for

each nest site. However, the values of HSI from the computer analysis of

127

standard environmental variables are not enough to accurately interpret actual
habitat suitability. Field observations need to be incorporated into the GIS
analysis. Field data are the key factor to understanding bald eagle behavior, the
portions of the landscape they use, their response to various disturbances, and
to accurately interpret the HSI values of each nest sites relative to their

reproductive success.

The modiﬁed HSI model is an improvement, but it still is not an optimum model.
Further research needs to be done to make the model more accurately correlate
with the ﬂedgling production. The modiﬁed model should be applied to other
FERC regulated impoundments in northern Lower Michigan since the same data
are likely to be available. The importance of this work is that there are many
FERC relicensing activities under way both in Michigan and the Upper Great
Lakes. The approach investigated in this study should be tried in several of
these other areas as a means of at least promoting discussion, although it is
probable that new eagle management insights will be gained. Federal and state
agencies are under statutory mandate to manage bald eagle habitat. The fact
that the quantitative model is at present not perfect is of lesser importance; it is
far better than nothing at all. The model will provide some information although
it must be recognizing that it is imperfect information. The spatial nature of the
model and the ability to rapidly modify it make possible the identiﬁcation of the

next important factors to be assessed.

 

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128

This thesis has made a contribution not only to professional wildlife managers
but also to the discipline of geography. This study falls into the realm of method
development under the spatial analysis tradition of the discipline and it certainly
falls under the human-environmental interaction portion of the discipline. Its

connections with biogeography, both flora and fauna, are obvious.

6.2 Suggestions For Future Research

It is suggested that a Geographic Information System (GIS) be used for further
evaluation of the modified HSI model. The federal and state agencies
responsible for bald eagle management plans should structure the data they
collect so that they can be readily used in a GIS (e.g. easily extracted from ﬁeld
records for later analysis). lmportantly, bald eagle nest locations and foraging
areas (keyed to specific eagle individuals) should be located on USGS
topographical maps for reference. The quantitative data related to the bald
eagles should be recorded in a database format. Bald eagle ﬁeld observations
need to be documented for each time period that the eagles are utilizing the

locations.

Recreational data is another key, missing component to answering several

questions for this study. Potential recreation data that may be helpful for future

 

129

modiﬁcations of the HSI model is the magnitude, range, and temporal
distribution of water-based recreation, the frequency of housing and camping
area use, and the disturbance intensity of camping and housing during the
nesting season, especially in the incubation period. Human disturbance has the
most critical impact on bald eagles during the egg-laying and incubating period
(Mathisen, 1969), and the highest mortality rate of bald eagles was at the egg
stage (Chrest, 1964). During these periods the nesting birds have the least
tolerance to external disturbances and may abandon their nests and leave the
area. Chrest (1964) recommended that during the incubation period human

activities should not be present around the nests.

Data regarding water-based recreation including boating, jet skiing, ﬁshing,
canoeing, and swimming are critically needed, especially in the Red Bridge
South and Red Bridge North territories. The response of the eagles to each of
these water-based activities, and the number and type of activity needs to be
inventoried and assessed. For example, the type of boat and the responses of
the eagles to each boat type, number of boats, and the activity from the boats in
the nesting area should be studied. In addition, the boat launch just downstream
from Red Bridge appears to promote the frequency and intensity of human
disturbances affecting the eagles of this area. These impacts must be more fully

studied.

130

The intensity and type of activity related to the response of bald eagles around
residential housing and the camping sites also needs to be addressed. The
focus of such an activity intensity study is to verify or modify the suitability graph
for human disturbance from housing and camping sites. SIV4 could be stored as
either area or point data as long as intensity of disturbance is the attribute. A
proximity analysis (distance weighting scheme) should be incorporated into the
disturbance intensity evaluation. Proximity captures the sense that the closer
the features are to the nesting eagles the greater the inﬂuence the feature has
on the eagles. The concept of proximity analysis is only practical using GIS
technology. All new variables should be considered as candidates for such
proximity weighting schemes. The interaction and intensity of human activities
(ﬁshing, boating, and swimming etc.) in the bald eagle foraging areas also

should be investigated.

More information is needed to indicate the food factor for the bald eagles. This
factor should include the amount and the location of ﬁsh in the reservoir, and
other important food sources for the breeding eagle when a ﬁsh source is not
available. The new food factors can be used to replace or to adjust the value of
SIV2. The SIV2 was estimated from the morphoedaphic index (MEI). The MEI
is the relation of the total dissolved solids (TDS units in ppm) to the average
mean depth of water. The total dissolved solids (TDS) data around each nest in

the Tippy Dam Pond does not exist. The TDS data that was used for this study

131

was from the quarterly water quality sample conducted during 1990 - 1991 by
Consumers Power Company. Water samples for the analysis of TDS were
gathered from mid-depth at the deepest portion of Tippy Pond in front of the
power house. The MEI was used according to Peterson (1986) from the study of
Ryder (1965) and Jenkins (1982) that ﬁsh biomass density were assumed to
increase with the MEI. A study of the actual ﬁsh biomass density should be
done to verify the relationship between MEI around each nest sites and the

potential feeding areas.

Most especially, it is clear that improved methods of spatial analysis of HSI are
required. In hindsight, the use of ﬁxed buffer zone widths/shapes for all factors
is inappropriate. Especially regarding the food factor, sites may be better
evaluated by using simple distance measures to known foraging areas. Again,
the requirement for ﬁeld observations is a limiting factor, but seems to be

absolutely necessary none the less.

 

APPENDIX

APPENDIX A

132

 

 

 

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