By Nathaniel Thomas Yost A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Fisheries and Wildlife Master of Science 20 20 ABSTRACT By Nathaniel Thomas Yost To monitor the status of waterfowl populations, the Michigan Department of Natural Resources (MDNR) beg an surveying abundance of breeding ducks and geese in 1991 and developed goals for waterfowl population and habitat management tied to the spring waterfowl survey. The spring waterfowl survey required flying a series of fixed - width transects using fixed - wi ng aircraft to estimate statewide abundance of Canada geese ( Branta canadensis ), mallards ( Anas platyrhynchos ), mute swans ( Cygnus olor ), and sandhill cranes ( Grus canadensis ) among others . To get consistent results, standard operating procedures (SOP) hav e been implemented and maintained across the years. Since observers did not see all birds from the fixed - wing aircraft, estimation of waterfowl abundance require d surveying a portion of transects with helicopters to establish visibility correction factors (VCF). MDNR used the VCF to adjust fixed - wing estimate s assuming observers saw all birds in transects flown with helicopters. To potentially improve precision and reduce costs, w e developed a lternate VCFs and aerial survey designs to understand how the accuracy and precision of the waterfowl population estimate change d from the existing SOP methodology . To meet MDNR standards, we considered alternate population est imate s that produced a coefficient of variation ( CV ) of less than 20% to be acceptable and worth consideration . We found comparable population estimates and CVs from eleven alternate VCFs and three alternate aerial survey designs compared to the SOP. iii ACKN OWLEDGMENTS This research was made possible due to the funding provided by the U.S. Fish and Wildlife Service through the Pittman - Robertson Wildlife Restoration Act Grant MI W - 155 - R, Michigan Department of Natural Resources (MDNR) , and the Department of F isheries and Wildlife at Michigan State University (MSU). This work was also partially supported by salary support for Scott R. Winterstein from the USDA National Institute of Food and Agriculture (Project No. M I CL02588). I will forever be indebted to thes e organizations for their support. I would like to thank my graduate committee, which was made up of Dr. David Luukkonen , Dr. Scott Winterstein, and Dr. Elise Zipkin. Their guidance, expertise, and support were instrumental in the completion of this project, as well as developing the skills to become a wildlife professional. In particular, I thank Drs. Luukkonen and Winterstein for being truly supportive advisors and mentors for providing me the opportunity to work on this project. They promoted me to grow professionally and personally during my time at MSU. I thank the MDNR for graciously letting me use their historic aerial survey data. I thank their observers, Bruce Barlow, John Darling, Brandy Dybas - Berger, Caleb Eckloff, Jeremiah Heise, Josh Imber, Nik Kalejs, Nate Levitte, Ben Luukkonen, Terry McFadden, Melissa Nichols, Mike Richardson, Joe Robinson, and Barry Sova, who helped with the data collection for 2018 and 2019 , as well as anyone else who has helped in previous years. I also thank Trey McClinton and Ashley Huinker for participating in the helicopt er surveys. I thank the pilots and support personnel of the Michigan State Police, Aviation Section for their assistance in completing the surveys each year. , Dr. Sarah Mayhew, for pr oviding and managing the database used in the spring waterfowl survey, as well as her expertise and guidance throughout the project. iv Lastly, program at MSU was exceptional for the supportive academic community I was surrounded by. my fellow graduate students who supported me with friendship and guidance throughout my masters. Lastly, I would like to thank my parents, Debbie and Gary, who have supported me from the beginning. Thank you for e ncouraging my love for science and supported me along the way. v TABLE OF CONTENTS LIST OF TABLE S ................................ ................................ ................................ ....................... v i LIST OF FIGURES ................................ ................................ ................................ ................... viii INTRODUCTION ................................ ................................ ................................ .......................... 1 Research Objectives ................................ ................................ ................................ ........... 9 METHODS ................................ ................................ ................................ ................................ ... 10 Study Area ................................ ................................ ................................ ........................ 10 Data Collection ................................ ................................ ................................ ................. 1 1 Data Analysis ................................ ................................ ................................ .................... 1 3 Statistical Analysis ................................ ................................ ................................ ........... 1 8 Alternate Visibility Correction Factors ................................ ................................ 1 8 Alternate Aerial Survey Designs ................................ ................................ ........... 21 Helicopter Bootstrap ................................ ................................ ............................. 2 5 Fixed - wing Bootstrap ................................ ................................ ............................ 2 6 RESULTS ................................ ................................ ................................ ................................ ..... 2 8 Survey Timing and Sample Sizes ................................ ................................ .................... 2 8 Alternate Visibility Correction Factors ................................ ................................ ......... 29 He l icopter Bootstrap ................................ ................................ ................................ ........ 5 5 Fixed - wing Bootstrap ................................ ................................ ................................ ....... 6 1 Alternate Aerial Survey Design s ................................ ................................ ..................... 7 1 DISCUSSION ................................ ................................ ................................ ............................... 9 1 Alternate Visibility Correction Factors ................................ ................................ ......... 9 1 Survey Timing and Sample Sizes ................................ ................................ .................... 9 6 Bootstrap Methods ................................ ................................ ................................ ........... 9 7 Alternate Aerial Survey Designs ................................ ................................ ..................... 98 MANAGEMENT IMPLICATIONS ................................ ................................ ........................ 10 6 APPENDI X ................................ ................................ ................................ ................................ . 1 09 LITERATURE CITED ................................ ................................ ................................ ............. 1 1 4 vi LIST OF TABLES Table 1. D escriptions of methods to estimate Visibility Correction Factors (VCFs) for the Michigan DNR spring waterfowl survey, including seven VCFs to compare against the Standard Operating Procedure ( SOP ) VCF ................................ ................................ ................................ ... 19 Table 2. Annual Visibility Correction Factor (VCF) for a) Canada goose, b) mallard, and c) sandhill crane , 1992 - 2019 . A VCF with 1 and SE of 0 is an ass umed value in table c before sandhill cranes were counted on VCF flights ................................ ................................ ................ 30 Table 3 . P opulation estimates, Coefficient of Variation s ( CV s ) , and costs to evaluate the helicopter - only design for Canada goose and mallard , 2003 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs .................... 8 0 Table 4 . P opulation estimates, Coefficient of Variation s (CV s ) , and costs to evaluate the helicopter - only design for Canada goose, mallard, and sandhi ll crane , 2010 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - onl y design costs ................................ ................................ ................................ ................................ ................ 8 1 Table 5 . P opulation estimates, Coefficient of Variation s (CV s ) , and costs to evaluate the helicopter - only design for Ca nada goose, mallard, and sandhill crane , 2014 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs ................................ ................................ ................................ ................................ ................ 8 2 Table 6 . P opulation estimates, Coefficient of Variation s (CV s ) , and costs to evaluate the helicopter - only design for Canada goose, mallard, sandhill crane, and mute swan , 2018 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs ................................ ................................ ................................ ............................ 8 3 Table 7 . P opulation estimates, Coe fficient of Variation s (CV s ) , and costs to evaluate the helicopter - only design for Canada goose, mallard, sandhill crane, and mute swan , 2019 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design c osts ................................ ................................ ................................ ............................ 8 4 Table 8 . P opulation estimates, Coefficient of Variation s (CV s ) , and costs to evaluate the modified SOP design for Canada goose, mallard, and mute swan , 2003 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs ................................ ................................ ................................ ............ 8 5 Table 9 . P opulation estimates, Coefficient of Variation s (CV s ) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2010 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs ................................ ................................ ........................... 8 6 vii Table 1 0 . P opulation estimates, Coefficient of Variation (CV) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2014 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs ................................ ................................ ................................ ............ 8 7 Table 1 1 . P opulation estimates, Coefficient of Variation (CV) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2018 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs ................................ ................................ ................................ ............ 8 8 Table 1 2 . P opulation estimates, Coefficient of Variation (CV) , and costs t o evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2019 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs ................................ ................................ ................................ ............ 8 9 Table 1 3 . Waterfowl grouping types for the M ichigan DNR spring waterfowl survey .............. 1 1 3 viii LIST OF FIGURES Figure 1. Map of M ichigan DNR spring waterfowl survey with east - west survey transects (4 - digit numbers) shown as solid lines. Transect numbers 5901 - 5912 (segment numbers 1 - 93) f arm u - 5811 (segment numbers 1 - 18 and 20 - 49) are in n orthern f forested stratum was removed . Farm urban stratum is shown in green, northern forested stratum is shown in red, and non - surveyable areas are shown in light blue ................................ ................. 5 Figure 2. Maps of a) Standard Operating Procedure (SOP), b) helicopter - only, and c) modified SOP. East - west survey transects (4 - digit numbers) are shown as solid lines, fixed - wing surveys are shown in the red outlined box, helicopter surveys are shown in the yellow outlined box, and non - surveyable areas are shown in light blue ................................ ................................ ................................ .......... 2 2 Figure 3. Comparison of Canada goose alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter survey s over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence interval s ................. 3 2 Figure 4. Comparison of mallard alternate Visibility Correction Factors (VCFs) using fixed - wing and helic opter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals ................................ ...... 36 Figure 5. Comparison of sandhill crane alternate Visibility Correction Factors (VCFs) using f ixed - wing and helicopter surveys over the state of Michigan for a) 2010, b) 2014, c) 2018, d ) 2019. The black bars represent ninety - five percent confidence intervals ................................ ...... 4 0 Figure 6. Comparison of Canada goose population estimates for alternate Visibility Corr ection Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals and n represents the number of segments to calcu late the VCF for each VCF estimation method ................................ ................................ ................................ ................................ ............ 4 3 Figure 7. Comparison of mallard population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018 , and e) 2019. The black bars represent ninety - five percent confidence intervals and n represents the number of segments to calculate the VCF for each VCF estimation method ................................ ................................ ................................ ................................ ........................ 4 7 Figure 8. Comparison of sandhill crane population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals and n represents the number of segments to calculate the VCF for each VCF estimation method ................................ ................................ ................................ ................................ ............ 5 2 ix Figure 9. Comparison of average Coefficient of Variation (CV) on population estimates for alternate Visibility Correctio n Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (2003, 2010, 2014, 2018, and 2019), b) mallard (2003, 2010, 2014, 2018, and 2019), and c) sandhill crane (2010, 2014, 2018, and 2019). CV of 20% is sho wn as the red dashed line. The black bars represent ninety - five percent confidence intervals .... ................................ ................................ ................................ ................................ ........................ 5 6 Figure 10. The bootstrap method population estimates for the helicopter - only aerial survey design using helicopter surveys over the state of Michigan for the f ive most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. The black bars represent ninety - five percent confidence intervals ................................ ................................ ........................ 5 8 Figure 11. The bootstrap method Coefficient of Variation (CV) on population estimates from the helicopter - only aerial survey design using helicopter surveys over the state of Michigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. CV of 20% is shown as the red dashed line ................................ ................................ ................... 6 2 Figure 12. Th e bootstrap method population estimates for the modified SOP aerial survey design using fixed - wing and helicopter surveys over the state of Michigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. Th e black bars represent ninety - five percent confidence intervals ................................ ................................ ........ 6 5 Figure 13. The bootstrap method Coefficient of Variation (CV) on population estimates from the modified SOP aerial survey design using fixed - wing and helicopter surveys over the state of Mi chigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. CV of 20% is shown as the red dashed line ................................ .................... 6 8 Figure 14. Comparison of population estimates among alternate aerial survey designs using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. The black bars represent a ninety - five percent confidence interval ................................ ................................ ................................ ................................ ........... 7 2 Figure 15. Comparison of average Coefficient of Variati on (CV) on population estimates among alternate aerial survey designs using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (2003, 2010, 2014, 2018, and 2019), b) mallard (2003, 2010, 2014, 2018, and 2019), and c) sandhill crane (2010, 2014, 2018, and 2019), and d) mute swan (2018 and 2019). CV of 20% is shown as the red dashed line. The black bars represent ninety - five percent confidence intervals ................................ ................................ ................................ ... 7 6 Figure 16. Comparison of indicated birds on the fixed - wing survey to the C oefficient of Variation (CV) on population estimates from the Standard Operating Procedure (SOP) aerial survey design using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (1992 - 2019), b) mallard (1992 - 2019), c) sandhill cr ane (2005 - 2019), and d) mute swan (2007 - 2019). CV of 20% is shown as the red dashed line ................................ ........................... 10 0 x Figure 17. Fixed - wing S tandard O perating P rocedure (SOP) for conducting the Michigan DNR spring waterfowl survey ................................ ................................ ................................ ............... 11 2 1 INTRODUCTION Highly mobile species can be difficult to monitor as the y cover large areas, including areas with restricted or limited access due to terrain or private land ownership (Caughley et al. 1976, Tracey et al. 2008). S ome population surveys may be difficult and expensive to conduct when surveying over a state or regional l evel. One solution is to conduct aerial surveys to estimate population size, particularly for large mammals and birds (Norton - Griffiths 1975, Caughley 1977). Aerial surveys have been extensively conducted to estimate regional and local abundance of North A merican waterfowl using fixed - wing aircraft (Martin et al. 1979, Smith 1995). One of the largest wildlife surveys takes place during the spring to estimate population sizes of waterfowl species in important breeding areas of Canada and the United States ( USFWS 2018); t he Waterfowl Breeding Population and Habitat Survey provides information on a wide variety of duck and goose species and helps to inform annual waterfowl hunting regulations. The MDNR collaborates with the U.S. Fish and Wildlife Service (USFW S), the Canadian provinces, and the Canadian Wildlife Service (CWS) to conduct aerial surveys from April to June to monitor important waterfowl populations across Canada and the northern United States (USFWS 2018). Beginning in 1991, MDNR began a pilot s tudy to survey distribution and abundance of waterfowl . Since 1991 , t h e MDNR has annually conducted the spring waterfowl survey to monitor population trends of breeding ducks and geese and develop ed goals for waterfowl population and habitat management (Cleveland 1994, Soulliere and Chadwick 2003). The MDNR spring waterfowl survey uses fixed - wing aircraft and helicopter s to estimate statewide 2 abundance of waterfowl with an emphasis on Canada geese ( B ranta canadensis ), mallards ( Anas platyrhynchos ), mute swans ( Cygnus olor ), and sandhill cranes ( Grus canadensis ). These species are of management concern because Canada goose and mallard are hunted species , and in some cases, high abundance s of Canada goo se, sandhill crane, and mute swan h as resulted in human - wildlife conflicts. In addition, waterfowl provide economic value and are good indicators of wetland habitat conditions (Grado et al. 2011, Hagy et al. 2016). Canada goose populations in Michigan hav e increased in the past 50 years with a corresponding increase in management demand to reduce human - goose conflicts through harvest or nest destruction as populations increased to over 300,000 birds in 2015 (Ankney 1996, United States Department of the Int erior 2005, Luukkonen et al. 2008). More recently, the MDNR has tried to reduce the population and achieve a statewide Canada goose abundance goal of between 175,000 - 225,000 birds based on the spring waterfowl survey (MDNR 2019). A concern for mallard abu ndance has recently become prominent due to the increase in droughts which has negatively impacted the number of wetland habitats in the prairie pothole region (PPR), one of the most productive waterfowl habitat s in the world (Johnson et al. 2005). Michigan mallard abundance is an indicator of breeding habitat conditions and so population monitoring can help detect wetland habitat loss. Ducks, especially mallards, use wetlands throughout their life for food, breeding, brood rearing, and cover from pr edators, so wetlands are an important habitat for ducks and a good predictor for where duck density may be the greatest (Krapu and Reinecke 1992, Austin et al. 2001, Anteau 2012 , Bartzen et al. 2017 ). With a potential decrease in wetland abundance, mallard productivity could decrease and impact mallard abundance, specifically in southeast Michigan based on a predictive model of mallard distribution ( Yerkes et al. 2007, Singer et al. 2016). Although 3 not been as negatively aff ected as the PPR , recent mallard abundance estimates for Michigan have been below expectations . E stimated wetland abundance in 2018 was slightly above the long - term average, although long - term climatic change predicts decreased quantity and quality of mall ard habitat (Singer et al. 2016, USFWS 2018). Sandhill crane abundance in Michigan has rebounded from declines caused by historic overharvesting and wetland habitat loss, and now significant human - crane conflicts through crop depredation are occurring ( Me ine and Archibald 1996, Avers et al. 2017). Due to their aggressive behavior, mute swans have been out - competing and displacing native species including trumpeter swans ( Cygnus buccinator ) and destroying native wetland habitat (Stone and Marsters 1970, Cia ranca 1990, MDNR 2012). In the case of the invasive mute swan, a DNR policy calls for reducing their abundance with a short - term goal of stabilizing numbers and a long - term goal of fewer than 2,000 birds (MDNR 2012). While these four species are the most abundant or important species counted using the MDNR spring waterfowl survey, other waterfowl species are recorded as well. Other species of dabbling ducks like wood duck ( Aix sponsa ), gadwall ( Mareca strepera ), American wigeon ( Anas americana ), green - wing ed teal ( Anas carolinensis ), northern pintail ( Anas acuta ), and northern shoveler ( Anas clypeata ) and diving ducks like ring - necked duck ( Aythya collaris ), canvasback ( Aythya valisineria ), lesser scaup ( Aythya affinis ), and greater scaup ( Aythya marila ), bufflehead ( Bucephala albeola ), long - tailed duck ( Clangula hyemalis ), hooded merganser ( Lophodytes cucullatus ), and common merganser ( Mergus merganser ) are detected on the aerial survey. Although the abundance of these waterfowl species is estimat ed from the spring waterfowl survey, they are not as well represented due to their low breeding abundance in Michigan . While the wood duck is a common species in Michigan, they are more prone to take 4 cover in forested wetland habitat which makes it difficu lt for observers to detect them , resulting in highly variable underestimates of their population size (Bellrose and Holm 1994). The MDNR spring waterfowl survey is a statewide survey with observers flying a series of 21 fixed - width transects using fixed - w ing aircraft (Figure 1; CWS and USFWS 1987, Smith 1995). Each transect is then made up of varying numbers of segments depending on the length of the transect. To get consistent results, standard operating procedures (SOP) have been implemented and maintain ed across the years (CWS and USFWS 1987; see Appendix for a full description of the SOP). Fixed - wing observers can fail to detect all birds and may misidentify waterfowl species which can result in population estimates with low precision and high bias (Gre en et al. 2008). Since detection is imperfect for observers in fixed - wing aircraft, a sample of fixed - winged segments have historically been resurveyed using helicopters (Caughley 1974). Helicopters provide d more reliable detection for observers . Additiona lly, helicopters are more maneuverable and efficient compared to fixed - wing aircraft (Ross 1985, Cordts et al. 2002). The MDNR has used visibility correction factor s (VCF s ), based on the helicopter flights, to correct fixed - wing counts, yield ing species - specific statewide abundance estimates that are thought to be less biased than uncorrected estimates . Helicopter surveys have not been flown every year due to expensive costs and labor constraints , so mean statewide species - specific VCFs from all VCF years have been used to correct annual fixed - wing survey counts. A new VCF is calculated for each VCF year, with a VCF year defined as a year in which both the fixed - wing and helicopter survey s are conducted. The n, the MDNR used c orrected mean fixed - wi ng density estimates from segment s to expand for the area of Michigan to compute population estimates. 5 Figure 1. Map of M ichigan DNR spring waterfowl survey with east - west survey transects (4 - digit numbers) shown as solid lines. Transect numbers 590 1 - 5912 (segment numbers 1 - 93) - 5811 (segment numbers 1 - 18 and 20 - forested stratum was removed. Farm urban str atum is shown in green, northern forested stratum is shown in red, and non - surveyable areas are shown in light blue . 6 To provide reliable results, s urvey methodologies need to periodically be examined and reevaluated , as many factors (e.g., weather, obse rvers, population demographics, and survey cost) could change over time (Cowardin and Blohm 1992, Tracey et al. 2008, Mills 2012, evaluated once. MDNR has not formally evaluated their current SOP survey design since 1994 (Cleveland 1994), so another evaluation of the survey is needed to determine if abundance estimates are reliable, cost - effective, and precise . A dditionally, the costs of aircraft, observers, an d survey stratification have changed. Since 199 1 , the MDNR has been using the same aerial survey field methods to provide consistent data collection . O aerial survey designs can be evaluated to determine utility for Michigan. For example, an assessment of wintering American black ducks ( Anas rubripes ) in the Atlantic flyway changed from a systematic sampling design to a stratified sampling design with multiple strata ( Conroy et al. 1988). This modification in their survey methodology helped to increase precision and adjust for underestimation from fixed - wing aircraft. Moreover, a recommendation for the Atlantic Flyway Breeding Waterfowl Survey to use hierarchical models to estimate waterfowl abundance instead of stratified random sampling was based on evaluating historical aerial survey data (Sauer et al. 2014). Lastly, the CWS and the USFWS jointly monitor American black duck populations in eastern Canada and the northe astern United States (Zimmerman et al. 2012). The CWS uses a helicopter plot survey while the USFWS uses a fixed - wing transect survey. After considering alternative models, they used a hierarchical model to aggregate and analyze data from both survey metho ds to obtain one population estimate for this region. Since many survey 7 might improve survey efficiency. Recently, helicopter costs for MDNR were reduced through a p artnership with the Michigan State Police (MSP) . Helicopter surveys are expensive but detect more birds compared to the fixed - wing survey. The MDNR was able to increase the number of helicopter flights , which also opened the possibility of using alternative aerial survey designs. One possibility could be to conduct the entire spring waterfowl survey only using helicopters. If the MDNR budget was not constrained, h elicopter surveys c ould be surveyed ever y year if possible, as observers in a helicopter have higher detection rates than observers in a fixed - wing aircraft . Currently , reduced expenses in helicopter costs may make a helicopter - only aerial survey design feasible. Alternatively, the MDNR could us e a modified SOP where some fixed - wing transects are removed to allocate more effort to helicopter surveys. An improved aerial survey design might minimize variance or achieve comparable precision on population estimates to the SOP from fewer transects, re ducing time and expenses for the spring waterfowl survey. To quantify precision, the MDNR uses the coefficient of variation (CV) which is a standardized measure of dispersion. The MDNR attempt s to achieve a CV of 20% or less on annual estimates of abundanc e for the spring waterfowl survey. A component that affect s the accuracy of the waterfowl population estimate using the SOP survey methodology is the species - specific VCFs used to correct the fixed - wing counts. Currently, the SOP uses an all - year (long - te rm) average species - specific VCFs. When the helicopter survey is conducted, each historic VCF is averaged with the current VCF. For example, eight VCF years exist from 1992 - 1996, 2003, 2010, and 2014. To determine the 1995 all - year VCF, the MDNR average d t he 1992, 1993, 1994, and 1995 VCF values. From 1992 - 8 1996 , the number and location of helicopter surveys were determined by cost, aircraft, and personnel time which might result in bias since the VCF segments were not representative of the state of Michigan (Cleveland 1994). The number of years selected to estimate VCFs will impact population estimates as well as the variance. If the MDNR uses all year s to estimate VCFs , population estimates may have increased precision, but th e long - term average VCF may not accurately estimate annual detection if there are changes to the system over time (i.e., changes in weather, observers, pilots, etc.; Soulliere and Chadwick 2003). A rolling average like a three or five - year statewide VCF est imate may be a viable alternative to accurately represent how the detection may change over time while also maintaining a CV of 20% or less on population estimates. 9 Research Objectives The purpose of this research wa s to evaluate the current SOP for the MDNR spring waterfowl survey by analyzing historical data (1992 - 2017) and by conducting two years of expanded helicopter surveys (2018 - 2019). This research also address ed if other aerial survey designs may be more cost - effective. The specific research objectives were as follows : 1) T o determine if modifications to existing MDNR survey methodologies can improve the precision of their aerial survey and estimation of waterfowl abundance. a. T o estimate visibility correction fact or s (VCFs) and determine if the current aerial survey methodologies are appropriate for estimating waterfowl abundance in Michigan . 2) To develop alternative aerial survey designs that estimate waterfowl abundance precisely and are comparable to the SOP metho dology (coefficient of variation [CV] less than 20%). a. To evaluate helicopter - only and modified SOP aerial survey designs to estimate precise waterfowl abundance (coefficient of variation [CV] less than 20%). 3) To determine the most efficient alternative aerial survey design s waterfowl. a. To conduct a statistical analysis to predict and compare waterfowl population estimates, coefficient s of variation (CV) , and cost s to determine the best aerial survey design s . 10 METH ODS Study Area from the spring waterfowl survey, the MDNR developed a stratified systematic sampling framework to survey the whole state of Michigan. MDNR biologists believed that the detection probability of wate rfowl was not constant throughout the state of Michigan (Cleveland 1994, Soulliere and Chadwick 2003). Thus, the MDNR considered stratification for the state of Michigan due to variations in cover type and land use. The MDNR divided Michigan into two strat a , the MDNR surveyed a sample of segments within each stratum (Figure 1). The farm urban stratum encompasses approximately the southern 1/3 portion of Michigan. The northern forested stratum consists of the remaining northern 2/3 portion of the state. The farm urban stratum is mostly defined by agricultural and urban land where plant pr oductivity and waterfowl densities are high. Wetlands are abundant in the farm urban stratum as loam soils dominate this stratum while clay and sandy soils comprise the northern forested stratum which retain s fewer wetlands. Ducks, geese, and swans are fou nd in and near wetlands, so high waterfowl abundance is associated with a higher number of wetlands in the farm urban stratum. Plant productivity and waterfowl densities are more variable in the northern forested stratum but mostly lower than in the farm u rban stratum. Although the spring waterfowl survey is a statewide survey, some areas of both strata were excluded from the survey. Portions of the hilly west ern Upper Peninsula, urban centers, and large airports, especially the Detroit Metropolitan Wayne C ounty Airport, were not surveyed due to safety concerns. 11 Data C ollection While historical data were used to conduct this project, we participated as observer s for the helicopter portion of the 2018 and 2019 spring waterfowl survey. The MDN R typically cond ucted the spring waterfowl survey during the months of April and May, but the start and end dates were variable and based on many factors. Survey t iming was critical for the MDNR spring waterfowl surveys to get the most accurate local breeding pair estimates (Dzubin 1969, CWS and USFWS 1987). The MDNR aimed to complete aerial surveys before nests from Canada geese hatched, when about half of the mallard females starte d nests, after migrant waterfowl have moved through an area, and when there was still good visibility by having less than 20% leaf - out on trees and shrubs (Soulliere and Chadwick 2003). W eather in Michigan can rapidly change within a season and vary among year s , resulting in earlier or later springs that can impact when the survey would begin . Surveys were not conducted on days with rain, fog, high winds, or other conditions that reduce d waterfowl detection and safety. Thus, long delays for the aerial surve y could occur if harsh weather persist ed for days. To get consistent results, the MDNR maintain ed standard operating procedures (SOP) for the spring waterfowl survey (see Appendix for a full description of the SOP ). Since there is a higher concentration o f breeding ducks and geese in the farm urban stratum, more transects were surveyed in th is stratum compared to the northern forested stratum. Hence, transects in the northern forested stratum are spaced 45.1 km (28 mi) apart while transects in the farm urb an stratum are spaced 22.5 km (14 mi) apart (Cleveland 1994). Once the MDNR collected the data, they grouped waterfowl observations into six categories: singles, flocked drakes, pairs, nesting pairs, nesting singles, and groups. The MDNR entered the data into a relational database used to estimate abundance by species. The relational database was a quick and efficient way to organize 12 large amounts of related data. The MDNR created quality control checks to eliminate most data entr y errors. They then entered each waterfowl observation into the database with the transect number, segment number, date, species , grouping type, and wetland type. Waterfowl the total n umber of as estimated for each segment. The number of singles, flocked drakes, pairs, nesting pairs, and nesting singles seen in a segment were each multiplied by two while the number of birds in a group were not adjusted to get the tota l number of indicated birds. Thus, indicated birds may include birds that were not seen but were assumed associated with a pair, for example. Since helicopter flights are expensive, the MDNR only conducted helicopter surveys in eight years prior to 2018 : 1992 - 1996, 2003, 2010, and 2014 . The MDNR began and has maintained an all - year averaged VCF for each species . The MDNR has surveyed from 139 to 152 segments for the fixed - wing flights. The number of segments surveyed with helicopters within a year ranged f rom six to 29 prior to 2018 . Some years had fewer segments surveyed because no flights were flown in the northern forested stratum in that year. In 2018 and 2019, we maintained the current survey methodology for transect numbers, transect configuration, t iming, and da ta collection for the spring waterfowl survey . However, we changed some survey methodology to evaluate changes in costs and precision . We aimed to conduct 40 helicopter segments for 2018 and 2019 VCF years , which was an increase from previous VCF years . We also changed to a new randomization for selecting helicopter segments to increase spatial representation for the state of Michigan (see below for a discussion of the new randomization). 13 Data Analysis The SOP aerial survey design use d fixed - wing density estimates and a statewide species - specific VCF to compute population estimates (Smith 1995) . The MDNR calculated d ensity estimates from the fixed - wing survey through the relational database and extrapolated for the whole stat e of Michigan , including areas of the state that are not surveyed . The y have used statewide species - specific VC F, based on the helicopter flights, to correct fixed - wing counts to add the number of indicated birds that were missed on the fixed - wing survey . h elicopter surveys were not flown every year due to budget and labor constraints , so average statewide species - specific VCFs from all VCF years were used to correct annual fixed - wing survey counts. Then, the MDNR used c orrected mean fixed - wing d ensity estimates from segments to expand for the area of Michigan to compute population estimates. We assumed that observers in helicopter surveys had a 100% detection , detections were statistically independent events , the number of birds in surveyed areas did not change in a segment between the fixed - wing and helicopter survey, and all birds were not double - counted and did not move before detection. While these are estimates, we do not fully know the true population size so 95% confidence intervals are used to deal with uncertainty in our estimates. We generated p opulation estimates using the SOP methodology as: where is the total abundance by species, is the total number of strata, j is th e stratum type, A j is the total area in stratum j , is the observed density per stratum, and is the average statewide species - specific VCF that is applied to each stratum j. (1) 14 We estimated as: ( 2 ) where y f is the total number of indicated birds on the helicopter in year f that is summed statewide , x f is the number of indicated birds on the fixed - wing aircraft in year f that is summed statewide , and F is the total number of years surveyed (Cochran 1977 ). For mallards, indicated birds can be expanded as: Indicated birds = (2*singles) + (2*flocked drakes ) + (2*pairs) + (2*nesting pairs) + (2*nesting singles) + number of birds in a group (Cowardin et al. 1995). The formula for Canada geese , sandhill crane, and mute swan is the same, except there are no flocked drakes to consider : Indicated birds = (2*singles) + (2*pairs) + (2*nesting pairs) + (2*nesting singles) + number of birds in a group is the observed density per stratum and calculated as ( 3 ) where is the mean indicated birds from the transects in stratum j from a fixed - wing, and is the mean area of the transects in stratum j (Martin et al . 1979). The variance on the population estimate is: 15 ( 4 ) where T is the total number of transects in stratum j, A is the area for transect t in stratum j, R is the average statewide VCF applied to transect t , B is the observed density per segment (Martin et al. 1979). T he variance components are: ( 5 ) where is the fixed - wing indicated birds per transect in stratum j, and B is defined in equation 3 . The associated variance on R is: ( 6 ) where k is the number of VCF segments in the stratum , is the helicopter indicated birds in stratum j, are defined in equation 4, and R is defined in equation 2 . Ninety - five percent confidence intervals on population estimates for the SOP can be calculated as: 16 ( 7 ) where is defined in equation 1 , is defined in equation 4 , and 1.96 is the critical z value when estimating a 95% confidence inter val using the normal distribution . To determine if the estimate from the survey method was precise, the coefficient of variation (CV) was computed. The MDNR uses a CV of 20% or less on annual estimates of abundance as a guideline for reasonable precision for the spring waterfowl survey. The CV was calculated as: ( 8 ) pilot s tudy (which will not be included in our analyses). Additionally, high helicopter costs have limite d the number of years in which to conduct the helicopter survey, and the number of helicopter segments sampled. Past VCF years (1992 - 1996) lacked randomness in th e selection of the s urveyed s egments and targeted areas with high waterfowl abundance. In 2003, the MDNR switched to a systematic random sampling approach. Beginning in the southernmost transect, the MDNR randomly selected a segment in every other transect , as well as the closest segment immediately north of the random segment. The MDNR a ttempted a target of 30 randomly selected segments across the state to achieve spatial coverage and assure representation in low and high waterfowl segments , but it was nev er fully achieved . The MDNR surveyed 27, 29, and 28 segments in 2003, 2010, and 2014, respectively. W e decided to achieve a target of 40 segments for each of the 2018 and 2019 survey years to determine if adding more than 10 helicopter segments was feasible under reduced helicopter expenses . To evaluate the SOP survey 17 methodology, we compared VCF years using surveys with more than 25 segments which include 2003, 2010, 2014, 201 8, and 2019 . F ewer than 25 segments resulted in higher variance on VCF estimates . In addition, the n orthern f orested stratum was not surveyed with a helicopter in 1992 and 1996. Starting in 2018, we used a generalized random tessellation stratified desig n (GRTS) to randomly select segments for VCF flights while maintaining a representative spatial coverage . GRTS sampling uses an algorithm that creates specific polygons called Dirichlet tessellation that is overlaid on a specified area (Gitzen et al. 2012) . Then, a randomly selected point will be surveyed within each polygon. GRTS sampling is more spatially balanced than a simple random sample. Furthermore, the least spatially balanced GRTS sample is comparable to the most spatially balanced simple random s ample (Gitzen et al. 2012). To compute a GRTS sample, we used R programming software (Version 3.6.1; https://www.R - project.org/ ) with package grts. Mute swans and sandhill cranes have limited data compared to mal lards and Canada geese. We did not analyze m ute swans for alternate VCF comparisons since we assumed that mute swans had a VCF value of 1 and a standard error of 0. Mute swans are large birds that are easily detected in a fixed - wing aircraft , so both surveys should have a 100% detection of seeing a mute swan on a segment. Additionally, helicopter surveys only began to count mute swans starting in 2018, so there were only two years of mute swan data with which to compare population estimate s t o alternate survey designs. Similarly, the MDNR began counting sandhill cranes in 2005 ; however, MDNR only estimated sandhill crane abundance from 2010 forward as 18 Statistica l A nalysis Alternate Visibility Correction Factors As an alternative to the use of long - term mean statewide species - specific VCF s , VCFs calculated for shorter intervals (e.g., annual, three - year average, or five - year average) could be used to correct fixed - wing counts. If there are temporal changes to the system, including occasional changes in observers, then alternate VCFs may better represent waterfowl species detection, thus more accurately estimating their populations. Furthermore, VCFs could be calculated for each stratum. We considered s even alternate VCFs: yearly statewide, three - year statewide, five - year statewid e, yearly stratum - specific, three - year stratum - specific, five - year stratum - specific, and all - year stratum - specific (Table 1 ). Comparing statewide to stratum - specific VCFs will determine if there are significant difference s in visibility detection between t he f arm u rban stratum and n orthern f orested stratum. The n orthern f orested stratum has a higher composition of vegetative cover in the landscape compared to the f arm u rban which may lead to a difference in waterfowl detection. T he number of years included in the estimation also likely influence s the VCF and associated variance . Detection may change over time due to observer error, change in helicopter aircraft or pilots , or covariates on the VCF (leaf - cover, weather, wind, etc.) . A single - year VCF or VCF calculated by averaging shorter time periods may be significantly different than the long - term average VCF. We estimated eleven alternate VCFs to determine if the SOP VCF is appropriate for estim ating waterfowl abundance as stratum - specific VCFs would yield two VCFs each year. We compared alternate farm urban, northern forested, and statewide VCFs to their all - year average VCFs for Canada goose, mallard, and sandhill crane. Analysis for alternate Canada goose and mallard VCFs used data from 2003, 2010, 2014, 2018, and 2019 19 Table 1. Descriptions of methods to estimate Visibility Correction Factors (VCFs) for the Michigan DNR spring waterfowl survey, including seven VCFs to compare against the Standard Operating Procedure (SOP) VCF . VCF Name Definition Equation Yearly Statewide The ratio of the total helicopter observations to the total fixed - wing observations for each species annually. (9) Three - Year Statewide The ratio of the total helicopter observations to the total fixed - wing observations from the past three VCF years. (10) Five - Year Statewide The ratio of the total helicopter observations to the total fixed - wing observations from the past five VCF years. (11) SOP All - years statewide VCF. The ratio of the total helicopter observations to the total fixed - wing observations for each species from all historic VCF years to the current VCF year. (2) Yearly Stratum - Specific The ratio of the total helicopter observations to the total fixed - wing observations for each species in each stratum annually. (12) Three - Year Stratum - Specific The ratio of the total helicopter observations to the total fixed - wing observations for each species from the past three VCF years for each stratum. (13) 20 VCF Name Definition Equation Five - Year Stratum - Specific The ratio of the total helicopter observations to the total fixed - wing observations for each species from the past five VCF years for each stratum. (14) All - Year Stratum - Specific The ratio of the total helicopter observations to the total fixed - wing observations for each species from all historic VCF years to the current VCF year for each stratum. (15) 21 helicopter survey years. Analysis for alternate sandhill crane VCFs used data from 2010, 2014, 2018, and 2019 helicopter survey years. To meet MDNR standards, any alternative VCFs that produced a CV of less than 20% w ere considered potentially acceptable. Alternate Aerial Survey Designs We analyzed data from the spring waterfowl survey to compare the current SOP survey design to a helicopter - only and modified SOP (Figure 2). A helicopter - only survey design was similar to the SOP, but there was no VCF and we derived population estimates only from helicopter counts. Helicopter data from 2003, 2010, 2014, 2018, and 2019 were used to calculate population estimates for the helicopter - only design for the given years. Comparable to the SOP, we estimated waterfowl a bundance and CV from the modified SOP aerial survey design using fewer fixed - wing transects. Therefore, the modified SOP design used the same population estimate and CV formulas as the SOP, but with modified survey effort. Fixed - wing data and VCFs estimate d for all years were used to calculate 2003, 2010, 2014, 2018, and 2019 population estimates for the modified SOP. The population estimate for the helicopter - only survey design was calculated as (16) where is the unbiased estimator for the total population, L is the total number of strata, is the total number of segments that can be available in stratum h, and is the sample mean in stratum h ( Thompson 1992) . The associated variance is then (17) 22 a) Figure 2. Map s of aerial survey design s for a) Standard Operating Procedure ( SOP ), b) helicopter - only, and c) modified SOP. East - west survey transects (4 - digit numbers) are shown as solid lines, fixed - wing surveys are shown in the red outlined box, helicopter surveys are shown in the yellow outlined box, and non - surveyable areas are shown in light blu e . 23 Figure 2 ( cont'd ) b) 24 Figure 2 (cont'd) c) 25 where is the sample size in stratum h, and is the sample standard error in stratum h. Population estimates for the helicopter survey design with a ninety - five percent confidence interval were calculated as (1 8 ) w here is defined in equation 16 and is defined in equation 17 . The CV was calculated for each SOP population as ( 19 ) Helicopter Bootstrap W e used the bootstrap method to determine how many helicopter segments are needed to achieve a CV of less than 20% with feasible costs. Bootstrapping is used when the underlying statistical distribution is unknown , so t he distribution of values found in random sample s from the population is a reasonable guide to the d istribution of the population estimate (Manly 1997). To approximate the population, the sample is resampled numerous times with replacement. We bootstrapped helicopter data from the 2003, 2010, 2014, 2018, and 2019 VCF years for Canada goose and mallard with a random sample of 10 to 90 segments with increments of 10. We randomly sampled with replacement from 27 segments in 2003, 29 segments in 2010, 28 segments in 2014, 40 segments in 2018, and 40 segments in 2019. To obtain confidence intervals for each segm ent sample size , we ran 1,000 iterations. We bootstrapped s andhill crane helicopter data from 2010, 2014, 2018, and 2019 and bootstrapped m ute swan helicopter data from 2018 and 2019. To determine the cost for each helicopter segment interval, we used the average 2018 and 2019 helicopter costs per segment to compare among the other VCF years. 26 Fixed - wing Bootstrap W e used bootstrap methods to determine how many fixed - wing transects can be removed to still achieve a CV of less than 20% with feasible costs. Savings in fixed - wing cost s could allow more VCF segments to be surveyed and may help to reduce the variance. Based on the sampling scheme for the spring waterfowl survey, we decided to only bootstrap the f arm u rban transects as there w ere twice as many segments in t his stratum as in the northern forested stratum . two segments, and transect 5912 contains one segment. We bootstrapped data from the 2003, 2010, 2014, 2018, and 2019 VCF years f or Canada goose, mallard, and mute swan. We bootstrapped s andhill crane fixed - wing data from 2010, 2014, 2018, and 2019. We randomly remov ed from one to 10 transects with increments of one . T ransect length varied among the 10 farm urban transects used for bootstrapping from six to 10 segments. To obtain the confidence interval for each transect sample size , we ran 1,000 iterations. We used the average 2018 and 2019 fixed - wing cost per transect to compare among the other VCF years. In order to make costs more comparable among years, we standardized the 2003, 2010, and 2014 costs to 2018 and 2019 costs. Based on the number of transects that w as removed, we created two modified SOP survey designs . We systematically remove d even - numbered transect s for the mo dified SOP , and systematically removed odd - numbered transects for the modified SOP - 2. For example, if the bootstrap method results in removing five transects, we would remove every even - numbered transect in the f arm u rban stratum for the modified SOP design (Figure 2c) , while the modified SOP - 2 design would remove every odd - numbered transect in the farm urban stratum . 27 W e calculated the cost for each aerial survey design and separated a ircraft costs into three categories: hourly rate, flight hours, and overtime charges. We estimated h elicopter costs per segment as : ( 2 0 ) where C is the total cost, r is the hourly rate for the aircraft, h is the flight hours, o is the total overtime charges, and n is the number of segments surveyed. We est imated f ixed - wing costs per transect as : ( 2 1 ) where t is the number of transects surveyed. We calculated t otal costs for each survey type as: ( 22 ) where C is the total cost, i is day i of the aerial survey, D is the total number of aerial survey days , and r, h, and o are defined in equation 20 . 28 RESULTS Survey Timing and Sample Sizes We initiated fixed - wing waterfowl survey s on 26 April 2018 and on 24 April 2019 and these dates were near the 1992 - 2017 average start date of 20 April with a range between 2 April to 30 April. The fixed - wing waterfowl survey concluded on 23 May 2018 and on 14 May 2019 and these dates were later t han the 1992 - 2017 average end date of 11 May with a range between 19 April to 24 May. W e flew a total of 40 18 - mile segments with helicopters in each of 2018 and 2019 in cooperation with Michigan State Police and MDNR personnel ; these flights included two observers and one trainee in addition to the helicopter pilot and were completed between 27 April and May 25, 2018 and 25 April and 17 May, 2019. These helicopter dates were near the average (1992 - 1996, 2003, 2010, 2014, and 20 18 - 2019) start date of 24 April with a range between 14 April and 1 May. The 2019 helicopter survey end date was near the average (1992 - 1996, 2003, 2010, 2014, and 2018 - 2019) end date of 16 May while the 2018 helicopter end date was later than the average end date with a range between 4 May and 19 May. We surveyed 40 helicopter segments in 2018 and 2019 and this number of segments was more than the 1992 - 201 4 average segments of 18 with a range of six to 29 segments. The 2018 spring waterfowl survey had a 4.4 - day difference between when the fixed - wing and helicopter surveys of the same segment were conducted, which was more than the average (1992 - 1996, 2003, 2010, 2014, and 2018 - 2019) time of 2.3 days with a range of one to 13 days. The 2019 spring waterfow l survey had a 1.4 - day difference which was less than the average. Helicopter flight hours per segment w as on average 1.16 hours in 2018 and 0.96 hours in 2019. Fixed - wing flight hours per segment was on average 0.4 hours in 2018 and 2019. Total flight hou rs , including commute time, for the helicopter survey was 46.4 hours in 2018 and 38.4 hours in 29 2019. Total flight hours for the fixed - wing survey was 51.6 hours in 2018 and 52.9 hours in 2019. We surveyed h elicopter segments in 2018 and 2019 using the GRT S methodology which resulted in a higher proportion of segments being surveyed in the northern forested stratum than in previous years. An average (1992 - 1996, 2003, 2010, and 2014) of 68% of the helicopter segments were located in the farm urban stratum compared to an average (1992 - 1996, 2003, 2010, and 2014) of 32% in t he northern forested stratum. In 2018 and 2019, 52% of the helicopter segments were located in the farm urban stratum compared to 48% in the northern forest ed . Canada goose VCFs ranged from 1.46 to 4.95 (Table 2 a). Mallard VCFs ranged from 1.91 to 6.48 (Table 2 b). Sandhill crane VCFs ranged from 1 .00 to 16 .00 (Table 2 c). Alternate Visibility Correction Factors Ninety - two percent of alternate statewide VCFs for Canada goose showed no significant difference compared to the Canada goose SOP (all - year average statewide) VCF for the five most recent VCF years since 95% confidence intervals overlapped (Figure 3). In 2003, the Canada goose yearly statewide VCF was significantly lower tha n the Canada goose SOP VCF. On average, the alternate statewide Canada goose VCFs were 15% smaller than the Canada goose SOP VCF. Similarly, ninety - two percent of alternate farm urban VCFs for Canada goose showed no significant difference compared to the C anada goose all - year farm urban VCF. In 2003, the Canada goose yearly farm urban VCF was significantly lower than the Canada goose all - year farm urban VCF. On average, the alternate farm urban Canada goose VCFs were 17% smaller than the all - year farm urban VCF. All the alternate northern forested VCFs for Canada 30 Table 2 . Annual Visibility Correction Factor (VCF) for a) Canada goose, b) mallard, and c) sandhill crane, 1992 - 2019. A VCF with 1 and SE of 0 is an assumed value in table c before sandhill cranes were counted on VCF flights . a) Year Number of Segments Fixed - wing Indicated Birds Helicopter Indicated Birds VCF SE 1992 7 68 201 2.96 0.34 1993 15 84 416 4.95 1.18 1994 12 89 438 4.92 1.16 1995 6 77 212 2.75 0.26 1996 17 115 343 2.98 0.72 2003 27 217 316 1.46 0.3 2010 29 229 665 2.9 0.38 2014 28 223 648 2.91 0.46 2018 40 406 891 2.19 0.35 2019 40 332 659 1.98 0.4 b) Year Number of Segments Fixed - wing Indicated Birds Helicopter Indicated Birds VCF SE 1992 7 138 411 2.98 0.7 1993 15 283 961 3.4 0.56 1994 12 138 894 6.48 1.19 1995 6 139 410 2.95 0.75 1996 17 228 652 2.86 0.66 2003 27 212 404 1.91 0.43 2010 29 265 550 2.08 0.43 2014 28 204 625 3.06 0.5 2018 40 218 540 2.48 0.45 2019 40 235 525 2.23 0.37 31 c) Year Number of Segments Fixed - wing Indicated Birds Helicopter Indicated Birds VCF SE 1992 7 0 NA 1 0 1993 15 0 NA 1 0 1994 12 2 NA 1 0 1995 6 0 NA 1 0 1996 17 2 NA 1 0 2003 27 2 NA 1 0 2010 29 14 49 3.5 1.77 2014 28 4 64 16 12.03 2018 40 18 56 3.11 1.19 2019 40 25 42 2.68 1.12 32 a) Figure 3. Comparison of Canada goose alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals. 33 b) c) 34 d) e) 35 goose showed no significant difference compared to the Canada goose all - year northern forested VCF. On average, the alternate northern forested Canada goose VCFs were 7% smaller than the all - year northern forested VCF. On average, alternate Canada goose VCFs were 11% smaller compared to the Canada goose SOP VCF. Alternate Canada go ose VCFs ranged from 1.18 to 3.45 and standard errors ranged from 0.17 to 2.00 for the five most recent VCF years. Variations in trends occurred in the Canada goose VCFs. Canada goose five - year farm urban, five - year statewide, all - year statewide, and SOP V CFs decreased each year while the remaining alternate VCFs showed no pattern in their respective VCF values. Canada goose northern forested VCFs had noticeably larger variances than the Canada goose statewide and farm urban VCFs. All the alternate statew ide and farm urban VCFs for mallard showed no significant difference compared to the mallard SOP VCF and the all - year farm urban VCF, respectively (Figure 4). On average, alternate statewide mallard VCFs were 16% smaller and farm urban VCFs were 15% smalle r compared to their respective all - year averaged VCF. Ninety - two percent of alternate northern forested VCFs for mallard showed no significant difference compared to the mallard all - year northern forested VCF. On average, the alternate northern forested ma llard VCFs were 11% smaller than the all - year northern forested VCF. On average, alternate mallard VCFs were 16% smaller compared to the mallard SOP VCF. Alternate mallard VCFs ranged from 1.06 to 4.38 and standard errors ranged from 0.19 to 1.33 for the f ive most recent VCF years. Mallard five - year farm urban, five - year statewide, all - year statewide, and SOP VCFs decreased each year while the other alternate VCFs showed no pattern in their respective VCF values. Confidence intervals for the mallard norther n forested VCFs were consistently larger than the mallard statewide and farm urban VCFs. 36 a) Figure 4. Comparison of mallard alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b ) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals. 37 b) c) 38 d) e) 39 Alternate statewide, farm urban, and northern forested sandhill crane VCFs showed no significant difference compared to the ir respective sandhill crane SOP VCF, all - year farm urban VCF, and all - year northern forested VCF (Figure 5). On average, alternate statewide VCFs were 8% larger, farm urban VCFs were 25% larger, and northern forested VCFs were 7% smaller compared to their respective all - year averaged VCF. On average, alternate sandhill crane VCFs were 15% larger compared to the s andhill crane SOP VCF. Some sandhill crane alternate VCFs were identical to each other because the observers in a helicopter did not survey for sandhill crane until the 2010 VCF year. Smaller fixed - wing observations on VCF segments for sandhill crane resul ted in VCF s that ranged from 1 .00 to 32 .00 with standard error s ranging from 0.52 to 24 .00 for the f our most recent VCF years. Sandhill crane three - year northern forested and all - year northern forested VCFs decreased each year while the other alternate VCF s and SOP VCF showed no pattern in the ir respective VCF value s . In 2010 and 2018, confidence intervals for the sandhill crane northern forested VCFs were greater than the sandhill crane statewide and farm urban VCFs. In 2014, sandhill crane yearly farm urb an and statewide VCFs were considerably larger than the other sandhill crane VCFs. Using the alternate VCFs, we then compared population estimates to the SOP population estimate. Alternate Canada goose population estimates were not significantly differe nt from the Canada goose SOP population estimate except for the 2003 Canada goose yearly statewide and stratum - specific VCF estimation methods which resulted in lower population estimates than the 2003 Canada goose SOP population estimate (Figure 6). On av erage, population estimates from statewide VCFs were 19% smaller for yearly, 17% smaller for three - year, 9% smaller for five - year compared to the Canada goose SOP. Stratum - specific population estimates were on average 18% smaller for yearly, 16% smaller fo r three - year, and 40 a) Figure 5. Comparison of sandhill crane alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2010, b) 2014, c) 2018, d) 2019. The black bars represent ninety - five percent confidence intervals. 41 b) c) 42 d) 43 a) Figure 6. Comparison of Canada goose population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals and n represents the nu mber of segments to calculate the VCF for each VCF estimation method. n = 50 n = 50 n = 77 n = 77 n = 84 n = 84 n = 27 n = 27 44 b) c) n = 79 n = 79 n = 106 n = 106 n = 113 n = 113 n = 2 9 n = 2 9 n = 107 n = 107 n = 134 n = 134 n = 141 n = 141 n = 2 8 n = 2 8 45 d) e) n = 147 n = 147 n = 174 n = 174 n = 181 n = 181 n = 40 n = 40 n = 187 n = 187 n = 214 n = 214 n = 221 n = 221 n = 40 n = 40 46 9% smaller for five - year compared to the Canada goose SOP. Population estimates from all - year stratum - specific VCFs were on average less than 1% smaller compared to the SOP. Moreover, the 2003 Canada goose yearly statewide and stratum - specific VCFs resulted in 50% smaller population estimates than the 2003 Canada goose SOP population estim ate. The 2003 Canada goose three - year statewide and three - year stratum - specific population estimates were around 28% smaller than the 2003 Canada goose SOP population estimate. In 2010, the Canada goose three - year statewide and three - year stratum - specific population estimates were on average lower than the Canada goose SOP by 20%. In 2014, the Canada goose three - year statewide, three - year stratum - specific, five - year statewide, and five - year stratum - specific population estimates were on average smaller than the Canada goose SOP by 15%. In 2018, the Canada goose three - year stratum - specific VCF had a similar population estimate compared to the Canada goose SOP population estimate, while the remaining alternate VCF estimates were an average of 14% smaller than t heir respective SOP population estimates. In 2019, the Canada goose population estimate for the all - year stratum - specific VCF was similar to the SOP population estimate. The rest of the VCF estimation methods estimated on average 16% smaller population est imates compared to the Canada goose SOP population estimate. For the five most recent VCF years, Canada goose population estimates for the stratum - specific and statewide VCF estimation methods showed marginal differences to each other per year. Variances f or each alternate VCF estimation methods were similar to the Canada goose variances based on the SOP. Few alternate mallard population estimates were significantly different from the mallard SOP (Figure 7) . I n 2003, the yearly statewide VCF estimation met hod resulted in a significantly lower population estimate than the SOP population estimate . On average, mallard population estimates from statewide VCFs were 23% smaller for yearly, 20 % smaller for three - year, 11% 47 a) Figure 7. Comparison of mallard population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence intervals and n represents the number of segments to calculate the VCF for each VCF estimation method. n = 50 n = 50 n = 77 n = 77 n = 84 n = 84 n = 27 n = 27 48 Figure 7 b) c) n = 79 n = 79 n = 106 n = 106 n = 113 n = 113 n = 2 9 n = 2 9 n = 107 n = 107 n = 134 n = 134 n = 141 n = 141 n = 2 8 n = 2 8 49 d) e) n = 147 n = 147 n = 174 n = 174 n = 181 n = 181 n = 40 n = 40 n = 187 n = 187 n = 214 n = 214 n = 221 n = 221 n = 40 n = 40 50 smaller for five - year compared to the mallard SOP. Stratum - specific population estimates were on average 20% smaller for yearly, 17% smaller for three - year, 9% smaller for five - year, and 3% smaller for all - year compared to the mallard SOP. In 2003, populat ion estimates from mallard yearly stratum - specific and yearly statewide VCFs were similar to each other and were around 44% smaller compared to the 2003 mallard SOP. Additionally, the 2003 mallard yearly stratum - specific VCF estimated about 11,000 fewer bi rds than the 2003 mallard yearly statewide but had a higher variance which resulted in no significant difference to the SOP. Similar patterns from the Canada goose population estimates repeated in the mallard population estimates. In 2003 and 2010, mallard three - year statewide and three - year stratum - specific population estimates were on average 23% smaller than their respective mallard SOP population estimates. Mallard yearly statewide and yearly stratum - specific population estimates were on average 31% sma ller in 2010 than the 2010 SOP population estimate. In 2014, the mallard all - year stratum - specific, yearly stratum - specific, and yearly statewide VCFs population estimates were nearly identical to the mallard SOP population estimate, while the remaining VC F estimation methods estimated an average of 18% fewer birds. In 2018 and 2019, similar patterns occurred for the alternate mallard VCF estimation methods. The mallard all - year stratum - specific VCF population estimate was slightly higher than the mallard S OP population estimate by 6% in 2018 and 3% in 2019. The rest of the alternate VCF estimation methods were on average around 14% smaller in 2018 and 17% smaller in 2019. In 2003, 2010, and 2014, mallard population estimates were marginally different betwee n stratum - specific and statewide VCF estimation methods. In 2018 and 2019, mallard population estimates had higher population estimate differences between stratum - specific and statewide VCF estimation methods. During 2018 and 2019, the mallard stratum - spec ific VCF estimation methods had higher population estimates than the statewide VCF 51 estimation methods. Variances for each alternate VCF estimation methods were similar to the mallard SOP variances in corresponding years. Sandhill crane alternate VCF estimation methods resulted in no significant difference compared to the SOP sandhill crane population estimates (Figure 8). On average, the population estimate from yearly statewide VCF was 25% larger compared to the sandhill crane SOP. Stratum - specific p opulation estimates were on average 33% smaller for yearly, 5% smaller for five - year, and 5% smaller for all - year compared to the sandhill crane SOP. Population estimates from three - year statewide, five - year statewide, and three - year stratum - specific VCFs were less than 1% different than SOP population estimates. Sandhill crane population estimates were similar to each other in 2010, but all the sandhill crane stratum - specific VCF estimation methods resulted in higher variances compared to the sandhill cran e statewide VCF estimation methods. In 2014, sandhill crane yearly statewide and yearly stratum - specific VCF population estimates were on average 170% more than the sandhill crane SOP and the rest of the alternate VCF estimation methods. Conversely, 2018 s andhill crane yearly statewide and yearly stratum - specific VCF population estimates were 34% smaller than the sandhill crane population estimates from SOP and other VCF estimation methods. In 2019, sandhill crane yearly stratum - specific and three - year stratum - specific population estimates were 39% smaller , while the yearly statewide population estimate was 23% smaller than the sandhill crane SOP population estimate. The remaining VCF estimation methods had negligible population estimate diff erences. Variances for each 2018 and 2019 alternate VCF estimation methods were similar to the variances for the sandhill crane SOP. 52 a) Figure 8. Comparison of sandhill crane population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) 2003, b) 2010, c) 2014, d) 2018, and e) 2019. The black bars represent ninety - five percent confidence interval s and n represents the number of segments to calculate the VCF for each VCF estimation method. n = 29 n = 29 n = 29 n = 29 n = 29 n = 29 n = 2 9 n = 2 9 53 b) c) n = 57 n = 57 n = 57 n = 57 n = 57 n = 57 n = 2 8 n = 2 8 n = 97 n = 97 n = 97 n = 97 n = 97 n = 97 n = 40 n = 40 54 d) n = 108 n = 108 n = 137 n = 137 n = 137 n = 137 n = 40 n = 40 55 Lastly, we looked at averaged CV on population estimates from 2003, 2010, 2014, 2018, and 2019. Averaged alternate Canada goose and mallard CVs on population estimates were not significantly different than their respective SOP averaged CV except for the si gnificantly higher yearly stratum - specific averaged CV for both species (Figures 9a and 9b). Furthermore, the yearly stratum - specific averaged CV exceeded the criteria of 20% or less with CV values at 21.2 for Canada goose and 21.6 for mallard. Based on th e overlap with the 95% confidence interval s , yearly statewide averaged CV s for Canada goose and mallard may be expected to exceed 20% in some years . For Canada goose and mallard, the variances on the alternate VCF estimation methods were similar to the SOP variances . Averaged alternate sandhill crane CVs were not significantly different compared to their respective SOP averaged CV (Figure 9c). Sandhill crane three - year statewide, five - year statewide estimation methods had nearly identical averaged CV s compa red to the sandhill crane SOP CV and with comparable variances. The stratum - specific methods for sandhill crane had comparable variances to each other but were exceedingly higher than the other alternate sandhill crane VCFs and SOP variances . The SOP metho d had the lowest averaged CV for Canada goose, mallard, and sandhill crane at 13.4, 13.1, and 39.9, respectively. Canada goose and mallard averaged CVs were less than 20% except for yearly stratum - specific. Averaged CVs for sandhill crane were always above 20%. Helicopter Bootstrap Using the five most recent VCF years, the bootstrap method resulted in decreased variance as the number of segments increased (Figure 10). Invariant population estimates were produced for each VCF year, showing that performing 1,000 iterations was sufficie nt for the bootstrap method. Canada goose and mallard bootstrapped CV showed that helicopter surveys 56 a) Figure 9. Comparison of average Coefficient of Variation (CV) on population estimates for alternate Visibility Correction Factors (VCFs) using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (2003, 2010, 2014, 2018, and 2019), b) mallard (2003, 2010, 2014, 2018, and 2019), and c) sandhill crane (2010, 2014, 2018, and 2019). CV of 20% is shown as the red dashed line. T he black bars represent ninety - five percent confidence interval s . 57 b) c) 58 a) Figure 10. The bootstrap method population estimates for the helicopter - only aerial survey design using helicopter surveys over the state of Michigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. The black bars represent ninety - five percent confidence interval s . 59 b) c) 60 d) 61 with more than 40 segments would result in a CV of 20% or less (Figures 11a and 11b). Sandhill crane and mute swan bootstrapped CV needed more than 40 segments to produce a CV of 20% or less (Figures 11c and 11d). For the five most recent VCF years, al l averaged Canada goose CVs were more than 20% if 10 helicopter segments were surveyed. Three VCF year s had more than 20% averaged Canada goose CV for 2 0 helicopter segments surveyed, while one VCF year had more than 20% averaged C V for 30 helicopter segme nts . At 40 helicopter segments surveyed, all the VCF years for Canada goose had an averaged CV of 20% or less. For averaged mallard CV, three VCF years at 10 helicopter segments, two VCF years at 20 helicopter segments, and one VCF year had averaged mallar d CVs more than 20%. At 40 helicopter segments surveyed, all the VCF years for mallard had an averaged CV of 20% or less. Averaged sandhill crane needed more than 80 helicopter segments to produce a CV of 20% or less. At 90 helicopter segments surveyed, av eraged mute swan CV was close to a 20% CV. Fixed - wing Bootstrap Similar to the helicopter bootstrap results, the bootstrap method resulted in decreased variance as the number of transects increased (Figure 12). Invariant population estimates were produced for each VCF year, showing that performing 1,000 iterations was sufficient for the bootstrap method. Canada goose and mallard bootstrapped CVs showed that no more than five transects should be removed in the farm urban stratum to maintain a CV of 20% or l ess (Figures 13a and 13b). Sandhill crane and mute swan bootstrapped CVs resulted in a CV of 20% or more for all number of transects in the farm urban stratum (Figures 13c and 13d). For the five most recent VCF years, all averaged Canada goose CVs were mor e than 20% if more than eight transects were removed in the farm urban stratum. One and two VCF years had averaged Canada goose CVs below a CV of 20% or less if seven transects or six transects were removed, 62 a) Figure 11. The bootstrap method Coefficient of Variation (CV) on population estimates from the helicopter - only aerial survey design using helicopter surveys over the state of Michigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. CV of 20% is shown as the red dashed line. 63 b) c) 64 d) 65 a) Figure 12. The bootstrap method population estimates for the modified SOP aerial survey design using fixed - wing and helicopter surveys over the state of Michigan for the five most recent VCF years for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. The black bars represent ninety - five percent confidence intervals. 66 b) c) 67 Figure 12 d) 68 a) Figure 13. The bootstrap method Coefficient of Variation (CV) on population estimates from the modified SOP aerial survey design using fixed - wing and helicopter surveys over the state of Michigan for the five most recent VCF years f or a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. C V of 20% is shown as the red dashed line. 69 b) c) 70 d) 71 respectively. Once five transects or less were removed, all the VCF years had averaged Canada goose CVs below 20%. For the five most recent VCF years, all averaged mallard CVs were more than 20% if more than eight transects were removed. Two and four averaged mallard CVs were below a CV of 20% or less if seven transect s or six transects were removed, respectively. At five transects removed, all averaged mallard CVs were below 20%. Averaged sandhill crane and mute swan CVs were always more than 20% CV. Alternate Aerial Survey Designs Although there was considerable vari ation among estimates from alternate aerial survey designs, there were no significant differences for Canada goose, sandhill crane, and mute swan population estimates compared to their respective SOP population estimates (Figures 14a, 14c, and 14d). Altern ate mallard population estimates also showed no significant difference from the SOP except for the 2003 helicopter - only method which was significantly lower than the SOP population estimate (Figure 14b). The modified SOP population estimates were always hi gher than their respective SOP population estimates, while the modified SOP - 2 population estimates were always lower than their respective SOP population estimates for all four species. On average, the modified SOP was 12% larger, 11% larger, 25% larger, 1 9% larger compared to the SOP population estimate for Canada goose, mallard, sandhill crane, and mute swan, respectively. On average, the modified SOP - 2 was 16% smaller, 14% smaller, 13% smaller, and 24% smaller compared to the SOP population estimate for Canada goose, mallard, sandhill crane, and mute swan, respectively. For Canada goose, the helicopter - only population estimates were on average 7% smaller than the SOP population estimate except for the 2014 helicopter - only population estimate which was 41% more than the SOP. Only the Canada goose helicopter - only population estimate was 72 a) Figure 14. Comparison of population estimates among alternate aerial survey designs using fixed - wing and helicopter s urveys over the state of Michigan for a) Canada goose, b) mallard, c) sandhill crane, and d) mute swan. The black bars represent ninety - five percent confidence intervals. 73 b) c) 74 d) 75 nearly identical to the SOP population estimate in 2018. For mallard, the helicopter - only population estimates were on average 17% smaller than the SOP population estimate. For 2003, 2010, and 2018, mallard population estimates averaged 36% smaller compare d to the mallard SOP population estimate. In 2014, the mallard helicopter - only population estimate was 25% larger than the SOP population estimate. In 2019, the mallard helicopter - only population estimate was similar to the SOP estimate, but 4% smaller. Th e sandhill crane helicopter - only population estimates were on average 9% larger than the SOP population estimate . I n 2010 and 2014 , the sandhill crane helicopter - only population estimates averaged 64% greater than the SOP population estimate . In 2018 and 2 019, the sandhill crane helicopter - only population estimates averaged 47% smaller than the SOP population estimate . The 2018 mute swan helicopter - only population estimate was similar to the SOP population estimate, while the 2019 mute swan helicopter - only population estimate was 193% larger at around 15,000 mor e birds than the SOP. For each VCF year, variances on the Canada goose and mallard population estimates were similar for each aerial survey design. Variances on the populat ion estimates for sandhill crane were comparable to the SOP variances except for the modified SOP and modified SOP - 2 in 2018 which were noticeably higher and the helicopter - only in 2019 which was lower. Variances on the 2018 mute swan modified SOP and the 2019 mute swan helicopter - only population estimates were higher compared to the ir respective 2018 and 2019 variances for the other three aerial survey designs. Averaged CVs on population estimates for alternate aerial survey designs were not significantl y different than their respective SOP averaged CV for Canada goose, mallard, sandhill crane, and mute swan (Figure 15). The SOP was the lowest averaged CV for Canada goose and mallard at 13.4 and 13.1, while the helicopter - only design was the lowest averag ed 76 a) Figure 15. Comparison of average Coefficient of Variation (CV) on population estimates among alternate aerial survey designs using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (2003, 2010, 2014, 2018, and 2019) , b) mallard (2003, 2010, 2014, 2018, and 2019), and c) sandhill crane (2010, 2014, 2018, and 2019), and d) mute swan (2018 and 2019). CV of 20% is shown as the red dashed line. The black bars represent ninety - five percent confidence interval s . 77 b) c) 78 d) 79 CV for sandhill crane and mute swan at 24.0 and 31.9. Canada goose and mallard CVs averaged over years were less than 20%, and averaged CVs for sandhill crane and mute swan were always above 20%. Based on the 95% confidence interval, the averaged Canada go ose SOP and modified SOP CVs comprised of CV values less than 20%, while only the averaged mallard SOP CV encompassed CV values less than 20%. For averaged sandhill crane CVs, the helicopter - only design had 95% confidence intervals that consisted of CV val ues less than 20%. The Canada goose modified SOP had comparable variances to the SOP while the helicopter - only and modified SOP - 2 variances were higher. The mallard modified SOP variance was higher than the variances on the other aerial survey designs. The sandhill crane helicopter - only variance was smaller than the variances on the other aerial survey designs. Lastly, mute swan helicopter - only and modified SOP had the smallest variances among the aerial survey designs. Lastly, we calculated population est imates, CVs, and costs associated with the helicopter - only and modified SOP designs for Canada goose, mallard, sandhill crane, and mute swan (Tables 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12). Costs for each alternate aerial survey design were based on the 2018 and 2019 spring waterfowl survey s which w ere $22,921 and $23,251 in 2018 and 2019, respectively . The fixed - wing survey cost on average $260 per transect in 2018 and $336 per transect in 2019. The helicopter survey cost on average $436 per segment in 2018 and $405 per segment in 2019. The cost for the helicopter - only design would be between $4,048 (1 0 segments) to $39,294 (90 segments). The cost of the modified SOP design would range from $19,554 to $22,242. Average costs to achieve a 20% CV on population estimates for the helicopter - only design for Canada goose, mallard, sandhill crane, and mute swan were respectively $13,942, $12,238, $22,185, and $35,839. Average costs to achieve a 20% CV on population estimates for the modified SOP design for Canada goose, mallard, sandhill crane, and 80 Table 3 . P opula tion estimates, Coefficient of Variations (CVs) , and costs to evaluate the helicopter - only design for Canada goose and mallard , 2003 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs. 200 3 Canada Goose Mallard Cost Number of Segments Population Estimate % CV Population Estimate % CV 2018 2019 10 124,562 29 164,330 20 $4,366 $4,048 20 123,923 23 163,408 15 $8,732 $8,097 30 124,253 19 164,376 12 $13,098 $12,145 40 124,080 17 163,570 10 $17,464 $16,194 50 123,897 15 164,376 9 $21,830 $20,242 60 123,653 14 163,446 8 $26,196 $24,290 70 123,392 12 163,821 8 $30,562 $28,339 80 123,562 12 163,939 7 $34,928 $32,387 90 122,829 11 163,907 7 $39,294 $36,436 81 Table 4 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the helicopter - only design for Canada goose, mallard, and sandhill crane , 2010 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs. 2010 Canada Goose Mallard Sandhill Crane Cost Number of Segments Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 10 245,930 24 216,920 21 19,910 41 $4,366 $4,048 20 245,347 19 218,734 16 20,075 31 $8,732 $8,097 30 245,196 15 218,924 13 19,961 25 $13,098 $12,145 40 244,123 13 218,149 12 19,971 22 $17,464 $16,194 50 244,574 12 218,995 10 19,619 20 $21,830 $20,242 60 245,412 11 218,599 9 19,893 18 $26,196 $24,290 70 245,456 10 218,872 9 19,584 17 $30,562 $28,339 80 245,790 10 217,883 8 19,638 16 $34,928 $32,387 90 244,999 9 217,988 8 19,890 15 $39,294 $36,436 82 Table 5 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the helicopter - only design for Canada goose, mallard, and sandhill crane , 2014 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine h elicopter - only design costs. 2014 Canada Goose Mallard Sandhill Crane Cost Number of Segments Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 10 276,84 7 21 268,710 16 29,172 37 $4,366 $4,048 20 274,275 16 268,286 11 28,878 28 $8,732 $8,097 30 271,981 13 269,460 9 28,906 23 $13,098 $12,145 40 272,113 11 269,000 8 28,848 21 $17,464 $16,194 50 273,750 10 268,940 7 28,635 18 $21,830 $20,242 60 272,001 9 268,602 7 28,568 17 $26,196 $24,290 70 271,160 8 269,281 6 28,497 16 $30,562 $28,339 80 272,060 8 269,852 6 28,518 15 $34,928 $32,387 90 273,073 7 270,087 5 29,141 14 $39,294 $36,436 83 Table 6 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the helicopter - only design for Canada goose, mallard, sandhill crane, and mute swan , 2018 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs. 2018 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Segments Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 10 276,693 37 177,032 35 18,542 33 12,107 54 $4,366 $4,048 20 281,330 28 172,298 26 18,468 24 12,059 42 $8,732 $8,097 30 281,538 23 174,273 21 18,430 20 12,044 35 $13,098 $12,145 40 275,425 20 171,808 19 18,431 17 11,889 31 $17,464 $16,194 50 280,217 18 171,823 17 18,499 15 11,798 28 $21,830 $20,242 60 279,130 17 173,442 15 18,458 14 11,907 26 $26,196 $24,290 70 278,395 16 172,918 14 18,476 13 11,701 24 $30,562 $28,339 80 279,816 15 173,660 13 18,430 12 11,924 22 $34,928 $32,387 90 277,738 14 172,477 13 18,542 11 11,916 21 $39,294 $36,436 84 Table 7 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the helicopter - only design for Canada goose, mallard, sandhill crane, and mute swan , 2019 . Two costs were calculated based on the 2018 or 2019 helicopter survey costs to determine helicopter - only design costs. 2019 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Segments Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 10 197,432 29 165,871 29 12,893 51 23,781 57 $4,366 $4,048 20 195,896 23 165,528 22 13,149 38 22,896 44 $8,732 $8,097 30 195,284 18 163,912 18 12,955 31 23,454 36 $13,098 $12,145 40 196,501 16 164,772 16 12,930 27 23,074 32 $17,464 $16,194 50 197,611 14 164,375 14 12,978 25 22,987 29 $21,830 $20,242 60 196,406 13 164,468 13 13,135 22 23,083 26 $26,196 $24,290 70 196,155 12 164,042 12 12,867 21 23,086 24 $30,562 $28,339 80 195,810 11 163,444 11 13,021 20 23,065 23 $34,928 $32,387 90 195,696 11 164,591 11 13,012 18 22,956 22 $39,294 $36,436 85 Table 8 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the modified SOP design for Canada goose, mallard, and mute swan , 2003 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs. 2003 Canada Goose Mallard Mute Swan Cost Number of Transects Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 1 221,195 38 301,077 31 2,726 134 $19,803 $19,554 2 221,119 29 303,940 23 2,575 85 $20,063 $19,890 3 221,058 24 303,061 19 2,544 64 $20,322 $20,226 4 220,429 21 304,217 17 2,584 52 $20,582 $20,562 5 218,472 19 304,049 15 2,517 44 $20,842 $20,898 6 219,697 17 303,410 14 2,492 40 $21,102 $21,234 7 219,174 16 303,303 13 2,546 35 $21,362 $21,570 8 219,372 15 303,631 12 2,532 32 $21,622 $21,906 9 218,746 14 303,612 11 2,521 29 $21,881 $22,242 86 Table 9 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2010 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs. 2010 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Transects Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 1 316,843 38 342,077 36 10,983 129 2,301 130 $19,803 $19,554 2 312,727 29 342,113 26 10,884 94 2,348 84 $20,063 $19,890 3 309,824 24 343,770 22 10,932 77 2,351 63 $20,322 $20,226 4 312,859 21 347,501 19 10,909 65 2,355 51 $20,582 $20,562 5 312,565 19 345,349 17 10,904 59 2,345 42 $20,842 $20,898 6 313,089 17 344,511 15 10,837 55 2,380 37 $21,102 $21,234 7 312,492 16 343,368 14 10,795 51 2,368 34 $21,362 $21,570 8 312,071 15 344,038 13 10,835 47 2,381 30 $21,622 $21,906 9 312,561 14 344,900 13 10,773 44 2,379 29 $21,881 $22,242 87 Table 1 0 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2014 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs. 2014 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Transects Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 1 197,440 34 218,262 37 21,918 121 7,468 120 $19,803 $19,554 2 195,714 25 217,733 28 21,035 84 7,641 81 $20,063 $19,890 3 196,597 20 217,253 22 21,005 67 7,884 58 $20,322 $20,226 4 195,757 18 221,602 20 21,054 57 7,537 49 $20,582 $20,562 5 194,398 16 219,268 18 20,826 52 7,922 41 $20,842 $20,898 6 195,302 15 220,242 16 20,672 48 7,742 37 $21,102 $21,234 7 195,654 13 220,628 15 20,563 45 7,817 33 $21,362 $21,570 8 195,613 13 220,930 14 20,568 42 7,818 29 $21,622 $21,906 9 195,594 12 220,880 13 20,623 39 7,721 26 $21,881 $22,242 88 Table 1 1 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2018 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs. 2018 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Transects Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 1 271,648 39 211,279 40 33,406 138 6,059 137 $19,803 $19,554 2 275,686 28 212,910 29 32,218 107 6,582 100 $20,063 $19,890 3 273,310 23 211,740 24 32,773 89 7,237 76 $20,322 $20,226 4 276,986 21 210,792 21 33,520 75 7,009 64 $20,582 $20,562 5 276,202 18 211,940 19 33,380 64 7,358 55 $20,842 $20,898 6 277,574 17 210,530 17 33,599 57 6,976 49 $21,102 $21,234 7 277,634 16 211,146 16 33,471 55 6,930 44 $21,362 $21,570 8 275,895 15 211,163 15 33,898 50 7,096 40 $21,622 $21,906 9 276,975 14 211,077 14 33,869 46 7,034 38 $21,881 $22,242 89 Table 1 2 . P opulation estimates, Coefficient of Variations (CVs) , and costs to evaluate the modified SOP design for Canada goose, mallard, sandhill crane, and mute swan , 2019 . Two costs were calculated based on the 2018 or 2019 MDNR spring waterfowl survey costs to determine modified SOP design costs. 2019 Canada Goose Mallard Sandhill Crane Mute Swan Cost Number of Transects Population Estimate % CV Population Estimate % CV Population Estimate % CV Population Estimate % CV 2018 2019 1 229,720 36 169,870 32 26,971 85 7,835 101 $19,803 $19,554 2 229,741 27 170,621 24 26,650 62 7,602 71 $20,063 $19,890 3 229,394 23 172,121 20 26,878 48 7,740 60 $20,322 $20,226 4 229,282 20 172,312 17 26,615 41 7,722 48 $20,582 $20,562 5 231,166 18 172,018 15 26,832 38 7,869 41 $20,842 $20,898 6 230,581 16 172,521 14 26,658 35 7,894 37 $21,102 $21,234 7 230,086 15 172,771 13 26,691 33 7,929 34 $21,362 $21,570 8 230,667 14 172,749 12 26,762 31 7,879 31 $21,622 $21,906 9 230,233 13 172,254 12 26,773 31 7,927 29 $21,881 $22,242 90 mute swan were respectively $20,807, $20,663, $24,410, and $24,188. The SOP design has achieved a CV of less than 20% for the past five VCF years for Canada goose and mallard. On average, the CVs from SOP population estimates were 13%, 13%, 40%, and 32% fo r Canada goose, mallard, sandhill crane, and mute swan, respectively. 91 DISCUSSION Alternate Visibility Correction Factors F ew of the alternate VCFs were significantly different than the SOP VCF for a given year. Although, while it should be noted that VCFs precision is positively related to sample size, we need to be cautious of using older data when estimating an all - year avera ge statewide VCF s . Data from 1992 is now 27 years old. Changes in technology, aircraft, observers, and landscape may alter waterfowl detection. Previously, VCF segments were not surveyed random ly and not indicative of the representation of the state of Mic higan, potentially violating the assumption that samples were independent and identically distributed. In addition, 1992 and 1995 VCF years did not survey the northern forested stratum. The 2003 survey added more VCF segments which increased the spatial re presentation within Michigan. A rolling average like a three or five - year statewide VCF estimate would be a viable alternative to accurately predict how the detection may change over time while also maintaining a CV of 20% or less on population estimates f or Canada goose and mallards . Five - year and three - year averaged VCFs were always within the 95% confidence interval of the SOP VCF for all three species. When the alternate VCFs were applied to estimate population size, five - year and three - year statewide a nd stratum - specific VCF estimation methods were comparable to the SOP population estimates . While the SOP had the lowest CV, the five - year and three - year statewide and stratum - specific VCF estimation methods were comparable. Additionally, the CV for the th ree - year statewide VCF estimation method was nearly identical to the SOP CV for the three species. With comparable population estimates and the lowest CV among the alternate VCF estimation methods, a three - year statewide VCF would be an acceptable alternat iv e to the SOP. 92 Population estimates for the yearly statewide and stratum - specific VCF estimation m ethods were consistently below the SOP since the all - year average VCF was higher than the yearly VCFs. In 2003, the yearly population estimates were considerably smaller than the SOP since the yearly VCF estimate was at its lowest for each of the species. As more years were surveyed, the all - year average VCF started to decrease since the yearly VCFs were getting smaller too, resulting in the population estimates based on the yearly VCF estimation methods comparable to the SOP in 2010, 2014, 2018, and 2019. Unexpectedly , the 2003 yearly statewide Canada goose and mallard population estimates and VCFs were significantly lower than their respective SOP population estimate and VCF. ds missed by the helicopter survey in 2003 which contributed to a lower yearly statewide VCF and subsequent smaller population estimate. They are unsure what caused this phenomenon , but some of the 2003 survey crew members recalled that the helicopter pilo ts were flying the helicopters at higher altitudes and speeds than the standard operating procedures. The 2003 survey used contracted pilots , so the helicopter pilots were new to the survey. New pilots that are not familiar with the SOP may have fl own the helicopter faster and higher than other VCF years, impacting the VCF. An increase in altitude and speed has a negative effect on detection (Caughley 1974). As altitude increases, waterfowl are less prone to flush from their habitat and exhibit a response t o the noise (Calef et al. 1976, Shupe and Beasom 1987, Tracey and Fleming 2007). As speed increases, observers have less time to detect and record birds (Caughley 1974). More broadly, detection could change over time due to other factors. Improvements in a ircraft could impact how observers in both fixed - wing and helicopter surveys detect birds (Clancy 1999, Soulliere and Chadwick 2003). Currently, the spring waterfowl survey uses Bell 93 407 , but Hughes 500 , Bell 430, and Bell 206 were used prior to 2018 . The Bell 206 was used in surveys before 2003, and the Bell 430 was used in 2010 and 2014. The Hughes 500 was used once in 2003. The difference in the helicopter model can impact visibility for front and rear seat observers (Tracey and Fleming 200 7 ). Front seat observers in a Hughes 500 have a bigger field of view than the rear seat observer, while the inverse is evident in the Bell Jet Ranger. Changes in the field of view could affect how many birds can be seen by an observer. However, both rear an d front seat observers are used for the helicopter survey so total waterfowl observations should remain the same. The difference in helicopter models can also contribute to variation in sounds produced by the aircraft. Tracey and Fleming (2007) found that Hughes 500 helicopters had a louder sound where more animals responded to the helicopter noise compared to Bell models . In 2003, waterfowl may have been alerted to the Hughes 500 much earlier than the Bell 206, resulting in waterfowl taking cover or flying out of the transect boundaries before the observers could count them. Surveys before 2003 relied on county road maps , air photos , and personal experience of the transect to follow the transect line and an imaginary line to delineate transect width. Starti ng in 2003, GPS technology was equipped to both the fixed - wing and helicopter surveys. Since helicopters circle wetlands and deviate from the centerline, the addition of GPS technology helped to prevent overcounting outside of the designated transect line ( Soulliere and Chadwick 2003). This may have led to fewer waterfowl observations on the helicopter than previous VCF years. Another factor potentially impacting VCF estimates was the MDNR switc h to a random sampling of VCF segments in 2003, whereas before the spring waterfowl survey sampled VCF segments with high waterfowl density. In 2003, more VCF segments were randomly sampled in the northern forested stratum which is more forested and has more variable or lower waterfowl 94 densities than the farm urban st ratum. In 2018, the MDNR switched to a GRTS sampling to achieve a better spatial representation of the population than a simple random sampling design (Gitzen et al. 2012). A slightly larger proportion of segments surveyed were in the northern forested str atum. The proportion of segments in the northern forested surveyed increased from 43% to 48% in the GRTS sampling. Since 2003, GRTS and random sampling have resulted in a more accurate representation of the waterfowl density for the VCF segments than the p revious sampling design from 1992 - 1996. Prior to 2003, fixed - wing densities on VCF segments were on average 101% larger for Canada goose and 59% larger for mallard compared to their respective fixed - wing densities on total segments. In 2003, 2010, and 2014 , fixed - wing densities on VCF segments using random sampling were on average 8% larger for Canada goose and 1% smaller for mallard compared to their respective fixed - wing densities on total segments. In 2018 and 2019, fixed - wing densities on VCF segments u sing GRTS sampling were on average 4% larger for Canada goose and 4% smaller for mallard compared to their respective fixed - wing densities on total segments. Observer error may impact how the VCF is estimated. Observer error can result in different visibil ity from one person to another. Observers may lack consistency, accuracy, or bias due to personal experience (Diem and Lu 1960). Untrained observers show high individual had a 91% detection rate while untrained observers had a 79% detection rate for ground - based surveys. For the spring waterfowl survey, each observer is trained on waterfowl identification and any new observers are a trainee for a year. Different levels of years observing could have slight impacts on how a person detects a bird. In addition, h igh waterfowl densities can increase observer error because observers have a more difficult time simultaneously recording 95 observations when new birds are being detected (Bart and Schoultz 1984, Nichols et al. 200 0 ). To maintain a consistent observer error throughout the years , a consistent crew of observers is important (Pearse et al. 20 08) . While standardized guidelines are in place to help maintain consistent data collection, observer error can still arise . Also, weather conditions such as cloud cover an d wind speed might affect detection; for example, bright sun can produce glare obscuring visibility of birds on water, depending on viewing angle relative to the horizon and azimuth. Often, swimming waterfowl leave a visible wake on the water surface under calm conditions and these wave patterns help observers detect birds except in windy conditions when wind - created waves obscure waterfowl movements (Shirkey 2012). Although the SOP had a higher number of segments surveyed to estimate the VCF, the alternat e VCF estimation methods had comparable CVs. The SOP had the lowest CV on the population estimate, showing that more segments surveyed resulted in a lower CV and a more precise population estimate. The variances on the alternate VCFs , including yearly alte rnate VCFs (27 to 40 segments), were similar to the SOP variances . Thus, the variance on the alternate VCF s contributed less to the total variance on the population estimate. Instead, variation in indicated birds and therefore bird density estimates on seg ments had a greater impact on the variance s on statewide population estimates . Since the alternate VCFs used the same fixed - wing indicated birds for each year, the variances were comparable. For example, the 2018 mallard CV had the highest mallard CV for t he past five VCF years. A large group of 150 mallards was detected on a segment during the fixed - wing s urvey which resulted in higher variance and CV on the population estimate . Mallard indicated birds in 2018 ranged from 0 to 26 without the group 96 of 150 m allards. When the 150 - mallard group was removed from the calculation, the 2018 CV on the population estimate dropped from 17.57 to 12.13. We found that the alternate VCF estimation methods for Canada goose and mallard resulted in comparable population estimates to the SOP since there were slight differences in the VCF values for the five most recent VCF years. On average, the alternate Canada goose VCFs were 11% smaller, and the alternate mallard VCFs were 16 % smaller than their re spective SOP VCFs. Alternate sandhill VCFs were on average 15% larger than their SOP VCFs due to high northern forested VCFs contributing to higher stratum - specific VCFs . Since the number of fixed - wing observations for a species remains the same to calcula te the population estimate, small changes to the VCF had a low impact on population estimates . Additionally, changing the VCF had a minimal impact on the CV. On average, alternate CVs for Canada goose, mallard, and sandhill crane were respectively 20%, 2 5 % , and 19% higher than their SOP CV. Survey Timing and Sample Sizes Survey timing has varied throughout the years, as spring weather in Michigan can change quickly. T he MDNR attempted to complete surveys during the specific survey timeframe (before nests from Canada geese hatched, half of the mallard females started nests, and when there was at least 20% visibility) , but it is difficult for the MDNR to monitor or to know if this survey timeframe was achieved or not . However, t he historic starting date of the survey was linearly related to growing degree - days near the starting transect (MDNR, unpublished data), suggesting that the criteria used to decide when to start the survey are strongly related to annual variation in plant phenology. Warmer weather can bring leaf - out earlier than expected which impedes visibility. Survey timing in 2018 and 2019 was variable but was not noticeably different than previous years based on the dates of the survey . The 2018 survey had an unexpecte d later end 97 date as wetlands and Lake Michigan in the upper peninsula were still frozen over, and a week of rain delayed the surveys. The 2019 survey commenced earlier than the 2018 survey, but a week of rain delayed the survey too. The delays in both year s also led to a longer time between when the fixed - wing and helicopter surveys were completed on the same segment. The spring waterfowl survey does not operate on the weekends, so it is possible to have at least a three - day difference in surveying the same segment. Leaf - out did start to occur for the last two survey years but did not hinder waterfowl detection as leaf - out was less than 20% on trees and shrubs. Helicopter segments are dependent on funding as early helicopter flights were costly, reducing th e number of helicopter segments surveyed. In 2010, a partnership between the MDNR and MSP developed, and helicopter survey costs became reduced. Helicopter surveys were important to the spring waterfowl survey, as the observers in helicopter detected more total waterfowl observations on average compared to the inexpensive fixed - wing surveys. Contributing to the expensive costs on the helicopter survey, flight hours per segment were longer in the helicopter compared to the fixed - wing. Total flight hours on t he fixed - wing were more than the helicopter, but cheaper hourly rates contributed to a more inexpensive fixed - wing survey. Bootstrap Met hods We found that the bootstrap method allowed us to estimate the variability of population estimates and CVs for alt ernate surveys, as well as creating 95% confidence intervals based on the sample for each VCF year (Manly 1997). The bootstrap method for Canada goose and mallard on the helicopter observations showed that 40 or more segments on average would result in a 2 0% or less CV on the population estimate for the helicopter - only design. If the budget or time is constrained in a given year, 30 helicopter segments may be acceptable since only the 98 2018 VCF year resulted in an averaged CV higher than 20% for Canada goose and mallard . The bootstrap method for Canada goose and mallard on the fixed - wing observations showed that removing less than five transects on average would result in a 20% or less CV on the population estimate for the modified SOP design. If the budget o r time is constrained in a given year, removing six or seven transects may be acceptable . T he averaged CVs for removing six or seven transects in the farm urban stratum for Canada goose and mallard were 24% or less. The bootstrap method for sandhill crane and mute swan resulted in undesirable CVs for both the helicopter - only and modified SOP . Higher CVs for sandhill crane and mute swan could be attributed to f ew fixed - wing observations , resulting in a high variation o n population estimates. The removal of transects would result in lower total flight hour s for the fixed - wing survey which would result in a lower fixed - wing survey cost. However, the precision o f the population estimate may be reduced , causing inaccurate population estimates . Al ternate Aerial Survey Designs No alternate aerial survey design was better or worse than the SOP survey design since the comparison of alternate aerial survey designs found no significant difference for the four species . Thus , the current transect number and configuration should remain the same . While the 2003 mallard population estimate for the helicopter - only design was significantly smaller than the 2003 SOP population estimate, the other four VCF years found no significant differences to their respecti ve SOP population estimate. Low helicopter observations in 2003 resulted in a lower yearly statewide VCF and helicopter population estimate. For 2003 mallard VCF segments, the helicopter survey counted 404 birds . Additionally, the helicopter survey counted 192 more birds than the fixed - wing observation which is less than the average difference of 302 birds. The 2003 mallard SOP population estimate was 130,000 birds more than what the 99 helicopter - only method estimated. Similarly, the 2003 Canada goose SOP population estimate was about 90,000 birds more than the 2003 helicopter - only population estimate. In 2003, the helicopter survey counted 99 more Canada geese on the helicopter than the fixed - wing which is lower than the average difference of 350 birds on VCF segments. Both the 2003 helicopter - only population estimate for Canada goose and mallard could have been impacted by a change in aircraft and pilot, sampling design, or observer error which also resulted in a smaller yearly statewide VCF. Averaged CV s showed that none of the alternate aerial survey designs are better or worse than the SOP. The SOP had the lowest averaged CV for Canada goose and mallard, showing that using both fixed - wing and helicopter surveys , including all the transects in the farm urban stratum, results in the most precise aerial survey method. Averaged CV s on sandhill crane and mute swan w ere higher for the SOP compared to the mallard and Canada goose CV on the SOP , but this may be attributed to low fixed - wing observations to estim ate a precise population. From the historical data and the 2018 - 2019 surveys, at least 750 indicated birds statewide on the fixed - wing survey sh ould result in a CV of less than 20% (Figure 16). Most VCF years were able to detect at least 750 indicated bird s on the fixed - wing survey for Canada goose and mallard which resulted in CVs on population estimates less than 20%. However, low indicated bird counts from the fixed - wing survey on sandhill crane and mute swans resulted in high CVs. On average (2010, 2014 , 2018, and 2019) , the fixed - wing survey counted 64 indicated birds for sandhill crane , while fixed - wing surveys for Canada goose and mallard detected over 700 indicated birds from the 2003, 2010, 2014, 2018, and 2019 VCF years . Mute swan averaged CV was similar for helicopter - only and SOP, although a higher variance on the SOP could be because few mute swans were detected on the fixed - wing survey. On average (2018 and 2019), t he fixed - wing 100 a) Figure 16. Comparison of indicated birds on the fixed - wing survey to the Coefficient of Variation (CV) on population estimates from the Standard Operating Procedure ( SOP ) aerial survey design using fixed - wing and helicopter surveys over the state of Michigan for a) Canada goose (1992 - 2019), b) mallard (1992 - 2019), c) sandhill crane (2005 - 2019), and d) mute swan (2007 - 2019). C V o f 20% is shown as the red dashed line. 101 b) c ) 102 d) 103 survey detected 148 mute swans. The helicopter - only design produced comparable population estimate s and CV s t o the SOP, especially for Canada goose and mallard. This shows that the helicopter - only design would be an acceptable alternate aerial survey desig n. Averaged CVs on the population estimate s for the helicopter - only design were below 20% for Canada goose and mallard but were only slightly higher than their respective averaged SOP CV. Averaged Canada goose CV increased by 31% from the SOP while average d mallard CV increased by 11% from the SOP using the helicopter - only design. We also noticed a pattern occurring for the helicopter population estimates. Whenever the yearly statewide VCF was smaller than the SOP VCF, the helicopter population estimate was smaller than the SOP population estimate, and the inverse occurred when the yearly statewide VCF was larger than the SOP population estimate. Since the helicopter survey corrects the fixed - wing counts, both the corrected fixed - wing and helicopter densities should be similar using a yearly statewide VCF under a randomized or GRTS sampling framework . Thus, the corrected fixed - wing density would be higher than the helicopter if the ye arly statewide VCF was lower than the SOP VCF for that given year . Due to the variation of yearly statewide VCF, the helicopter population estimate should randomly be above or below the SOP population estimat e . Based on the helicopter bootstrap, the surve y would cost between $16,194 and $17,464 to survey 40 segments. The helicopter - only design would cost between $5,786 and $6,726 less than the SOP design. Labor costs would also be reduced for the MDNR since they would not have to spend funds on the fixed - w ing survey and take time away from their employees to conduct the survey. Savings and reduce d labor costs make the helicopter - only design an affordable option if the MDNR chooses to modify the spring waterfowl survey. 104 We found that savings on removing fixed - wing transects in the farm urban stratum were minimal. With each transect removed, the MDNR could save on average $300 per transect. By removing five transects in the farm urban stratum, the modified SOP designed wou ld save $1,500 and still achieve a CV of 20% or less. The MDNR could then use these funds to allocate for more helicopter segments. However, helicopter surveys cost on average $420 per segment which equates to adding three more helicopter segments. Based o n the helicopter bootstrap, three additional helicopter segments would not gain enough precision to warrant the need for more helicopter segments surveyed. While the modified SOP aerial survey design is an acceptable alternate aerial survey design, there a re not enough benefits gained to change from the SOP aerial survey design. Both the modified SOP and modified SOP - 2 gave comparable results . R emov al of only odd or even transects does not change outcomes , although the modified SOP had a higher population e stimate t han the SOP , and the modified SOP - 2 had a lower population estimate than the SOP . The difference between population estimates on modified SOP and modified SOP - 2 may be related to differences in wetland habitat conditions , resulting in slightly mor e birds on average in the odd - numbered transects. Averaged Canada goose and mallard CV increased by 17% and 14% from the SOP using the modified SOP , respectively. Averaged Canada goose and mallard CV increased by 9% and 13% from the SOP using the modified SOP - 2 . However, the MDNR may believe that a saving of $1,500 could be worthwhile. In addition to saving money, MDNR employees conducting the fixed - wing survey would have fewer days in the field and could utilize their time performing other activit ies . On average, observers complete the fixed - wing farm urban stratum in five days, so reducing the number of transects in half could complete the farm urban stratum in two or three days. 105 We also noticed that costs for fixed - wing and helicopter surveys ca n be dependent on MDNR overtime hours expense whenever the pilots go over their allotted work hours. This is e changes daily, and the MSP oversees schedul ing a pilot for each survey day. For the fixed - wing survey, $658 and $867 were defined as overtime charges in 2018 and 2019, respectively. For the helicopter survey, $2,057 and $1,716 were charged as overtime ex penses in 2018 and 2019, respectively. If future changes are to be made, the MDNR should be prudent that estimated costs could go slightly over based on overtime charges occurring. 106 MANAGEMENT IMPLICATIONS Aerial surveys with precise estimates o f abundance provide important information used in setting annual hunting regulations for waterfowl and other birds. The MDNR depends on recreational waterfowl hunting as a source of funding for wildlife and habitat management, as well as providing informat ion about waterfowl movement patterns, survival rates from band reporting, and management of overabundant species like Canada geese (Miller and Vaske 2003, Garrettson et al. 2014). Each year, the MDNR reports the waterfowl population estimates from the spr ing waterfowl survey to the USFWS. For waterfowl management, Michigan is part of the Mississippi flyway which consists of representatives from U.S. state and Canadian provincial wildlife management agencies within the region. Together, the USFWS and the Mi ssissippi flyway set frameworks for harvest regulations based on the Adaptive Harvest Management program (AHM) which regulates daily bag limit, season length, and opening and closing dates (Williams et al. 1996, USFWS 2018). Although harvest of mallard pop ulations is managed at the f lyway scale and larger, the state of Michigan can make decisions to help manage mallards more locally. For example, t he MDNR can propose their own specific waterfowl hunting season regulations for Michigan that cannot be more liberal than the federal framework but can be more conservative. With recommendations from the Citizens Waterfowl Advisory Committee (CWAC) and other public i nput, the MDNR will recommend Michigan waterfowl hunting season regulations to the Natural Resources Commission. The CWAC is a group of dedicated civilians that provides feedback on proposed Michigan waterfowl regulations for the next year, as well as any waterfowl hunting issues (MDNR 2017). Finally, the MDNR presents recommendations to the Natural Resources Commission to make the final decision for waterfowl hunting regulations in Michigan. 107 Considerable evaluation should be considered when choosing the t ype of monitoring technique depending on the species and management questions (Lancia et al. 2005). Monitoring programs like the spring waterfowl survey need to have specific objectives in place that estimate abundance with high precisions while also minim izing the cost (Reynolds et al. 2011). Alternate aerial survey designs would be considered acceptable if the estimation of waterfowl abundances is precise by meeting a CV of less than 20% without increasing the cost s . We believe that the current transect n umber and survey configuration is still the best waterfowl monitoring program for the state of Michigan as alternative options did not produce enough benefits to outweigh the disadvantages. The modified SOP design was slightly cheaper than the SOP method b ut resulted in a higher CV for both the modified SOP and modified SOP - 2 . The helicopter - only method is about $6,000 cheaper than the SOP method but also resulted in slightly higher CV s . If helicopter survey costs continue to decline, the helicopter - only de sign could be a viable alternative aerial survey design as more helicopter segments could be surveyed, reducing the CV . A trade - off occurs between the fixed - wing and helicopter. Fixed - wing aircraft are cheaper but observers in a fixed - wing aircraft detect fewer birds. Helicopter surveys are more expensive and take longer than a fixed - wing survey, but observers in helicopters detect more birds. We believe it is important to combine the benefits of both aerial surveys by using the SOP aerial survey design in estimating waterfowl abundance. We recommend t hat the MDNR maintain the current transect number and configuration for the spring waterfowl survey, but we caution continued use of older data. Many factors (e.g., weather, observers, population demographics, and survey cost) could change detection annually (Cowardin and Blohm 1992, Tracey et al. 2008, Mills 2012, Ransom 2012, Schummer et al. 2018). Thus, we recommend incorporat ing a three - year average statewide VCF as this VCF 108 estimation method better capture s annual variation than the SOP VCF . A three - year average statewide VCF would also be preferable as the CV is nearly identical to the SOP CV and lines up with decision frameworks for some species like Canada geese that use three - year cycles. On average, th e three - year statewide VCF estimate d 1 7 % and 20 % fewer birds than the SOP population estimate for Canada goose and mallard, respectively . If the MDNR is concerned about incorporating a shorter time interval averaged VCF in the population estimates for Canada goose and mallard, then a five - year statewide would be more appropriate. The five - year statewide population estimate s were on average 9% and 11% smaller than the SOP population estimate for Canada goose and mallard, respectively. We would also advise the MDNR to conduct the helicopter survey every year if possible, to continuously update the VCF for each species , as year - to - year variability occurs . However, we understand that annual helicopter surveys are still expens ive, so we would recommend conducting helicopter surveys every other year or once every three years. We recommend that a minimum of 40 VCF segments should be conducted every VCF year and to continue using the GRTS sampling. I f the MDNR considers the altern ate aerial survey designs, then we recommend the helicopter - only design to be surveyed with 40 or more helicopter segments and the modified SOP design to be surveyed by removing no more than five transects in the farm urban stratum. The spring waterfowl su rvey may be reexamined if helicopter survey costs continue to reduce and become similar to fixed - wing survey costs, as the helicopter - only design may be reconsidered. No matter what aerial survey design the MDNR chooses, the same observers should be used in each survey platform to helped to inform the MDNR that modifications to the existing methodology should be incorporated . 109 APPENDIX 110 APPENDIX The MDNR spring waterfowl survey is a statewide survey that involves flying a series of 21 fixed - width transects using fixed - wing aircraft (Figure 1 7 ; CWS and USFWS 1987, Smith 1995). To get consistent results, the MDNR follow an accomplishment di rective to create standard operating procedures (SOP) for the spring waterfowl survey (CWS and USFWS 1987, B. Avers, MDNR, unpublished report). The SOP survey methodology has fixed - width transects that are 0.4 km (1/4 mi) wide. Surveys are flown along an e ast - west orientation to avoid visibility error from the sun. Each transect is divided into segments that are 29 km (18 mi) long. The total number of historic segments have ranged from 139 to 152. Due to differences in terrain and feasibility of conducting fixed - wing surveys, the aircraft is flown at an altitude between 0.03 - 0.05 km (100 - 150 feet) and speed between 144.8 - 169.0 kph (90 - 105 mph) throughout the survey. Using a Cessna 172, 180, or 260 plane, fixed - wing surveys travel along the segment line and c onsist of a pilot with a front and rear seat observer. Surveys were not flown when beginning wind speeds exceeded 25 kph (15 mph) or when wind speeds reached 40 kph (25 mph) during the day. Both observers identify all waterfowl species from 0.2 km (1/8 mi ) on their side of the segment line. They also record the wetland type for each waterfowl observation and the segment number. To determine in a fixed - wing aircraft if the wetland is within 0.2 km from the segment line, a clinometer is used to measure this appropriate angle. The tape is placed on the wing struts to help guide observers on the segment edge location. Any bird above the tape line is out and not recorded. In addition to recording waterfowl observations, rear - seat observers record every wetland t hat they see within the segment even if there are no waterfowl observations for an estimate of total statewide wetlands. 111 For each segment surveyed, a front and rear seat observer record waterfowl observation and assign them to one of six grouping categori es: singles, flocked drakes, pairs, nesting pairs, nesting singles, and groups (Table 1 3 ). For both fixed - winged and helicopter surveys, the total breeding biology. Drakes, flocked drakes, and pairs are adjusted by a multiplier of two while groups are not adjusted. To reduce misidentification bias, each crew member is trained in waterfowl identification. Since not all birds are seen by observers in the fixed - wing aircraft (i.e., detection probability is <1), estimation of waterfowl abundance through the SOP survey design requires surveying a sample of segments with helicopters to establish species - specific visibility correction factors (VCF; Caughley 1974). Helicopter surveys follow the same protocols as the fixed - wing surveys with slight variations. Segments are surveyed in a quadratic grid that is 0.2 km (1/8 mi) from either side of the segment line and wetlands within the segment are circled, allo wing for more complete counts of waterfowl. To be accurate, the pilot uses Global Positioning Systems (GPS) to determine how far off the transect centerline is to the helicopter. Using Hughs 500 or Bell Jet Ranger, helicopter surveys are not flown every ye ar because they are expensive and require additional personnel time. Historically eight VCF flights were conducted, in 1992 - 1996, 2003, 2010, and 2014, with 2018 and 2019 survey years conducted during this thesis. The ratio of the helicopter to fixed - wing counts create s a visibility correction factor that is applied to correct the fixed - wing counts. The SOP averages statewide species - years. Corrected fixed - wing density estimates from each segment are then expanded for the area of Michigan to compute population estimates. 112 Figure 1 7 . Fixed - wing S tandard O perating P rocedure (SOP) for conducting the Michigan DNR spring waterfowl survey. 113 Table 1 3 . Waterfowl grouping types for the M ichigan DNR spring waterfowl survey. Grouping Type Species Definition Singles All Record the number of lone males with the absence of a female. Flocked Drakes Ducks Record the total number of males observed together with the absence of females. Only record for two to four drakes. 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