1.34. 5 2 I“. l with} < ”rt 5‘. to: olfqh TC. 510 ‘2‘”‘53 331141"- 4 x a; '\ m}. a gym.» “VI. . 6.0%. in [:1 Ifi‘fiic; : m .zi WW ME we... .._( a «w 3 E .,.\. gm.” 5 .mm WW” d. 1‘ a” . “N f1-“ .3 5m Mu. A. AK.‘ at 0&1. “In“ ‘mMu x H 8 wm H... 3% v. a .0. 3 m... a. . an i... am. 3‘!" I b Asuzz I ‘3 ‘11: ,,,,,,_,,.,,.,_,g :2: i::._,:: m... LIBRARY Michigan Stat: University .' (u.- "sun— _—..-n- MEASURING PARASITE DAMAGE TO COTTONTAILS WITH PACKED-CELL VOLUMES by Benjamin F. Tullar Jr. AN ABSTRACT OF A Thesis submitted to the College of Agriculture of Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 1961 M. $4 3 $7404 M £3 MEASURING PARASITEmDfilAGE TO COTTONTAILS PACKED-CgiiHVOLUhLS ABSTRACT In order to investigate the possibility of parasites being partially responsible for fluctuations in cottontail populations, numbers of warbles, ectOparasite-loads and packed-cell volumes were determined for 138 rabbits captured at the Kellogg Bird Sanctuary and Forest from July 1 to December 22, 1959. The packed-cell vol- ume distributions showed a significant increase from July to Dec- ember. Statistical analysis of the packed-cell volumes of infant, juvenile and adult rabbits showed no differences attributable to age or bodydweight. However, a highly significant negative correl- ation was found between packed-cell volume and minimum temperature. Comparisons of packed-cell volume means of groups of rabbits harboring warbles, hemoflagellates and fleas were made with groups captured in the same periods which were found free of these para- sites. The results indicated that warbles and hemoflagellates caused no differences in red blood cell levels of infested rabbits. A slight decrease in packed-cell volume was observed to be caused by moderate flea infestations but this was not significant. The very few observations of light tick infestations also appeared to lower packed-cell volumes but the evidence was insufficient. It was found that greater contrasts in ectoparasite infesta- tions could be observed during late winter and early spring. How- ever, the writer thinks that a more complete blood analysis is necessary to show the degree of damage caused by parasites. MEASURING PARASITE DAMAGE TO COTTONTAILS WITH PACKED-CELL VOLUMES by Benjamin F. Tullar Jr. A THESIS Submitted to the College of Agriculture of Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife .1961 ACKNOWLEDGEMENTS I wish to express my gratitude to Dr. George A. Petrides, Professor of Wildlife Management, Michigan State University, for his help and encouragement in the field work and in the preparation of this manuscript. I also thank Dr. David T. Clark, Professor, Department of Microbiology and Public Health, Michigan State University, for providing equipment and facilities for the laboratory phase of the project and for advice on technical aspects. I am also greatly indebted to Messrs. Roswell D. Van Deusen and Walter Lemmien, Managers of the Kellogg Bird Sanctuary and the Kellogg Forest, respectively, for providing equipment for rabbit trapping and for advice and encourage- ment. I also thank Dr. Peter I. Tack, Department Head, and Dr. Leslie W. Gysel, Professor, Fisheries and Wildlife Department, for their help in the final stages of manuscript preparation. I. '0 INTRODUCTION The objective of this study was to investigate the para- sites of cottontail rabbits (Sylvilagus floridanus) as possible limiting factors of their populations. This project was conducted at the W.K. Kellogg Bird Sanctuary and Forest, Kalamazoo County, Michigan. Data were collected in conjunction with a long-range cottontail research program sponsored by the Department of Fisheries and Wildlife, Michigan State Univ- ersity, and supported in part by the Wildlife Management. Institute. Rabbit pqpulations fluctuate within and between_years Annual spring and autumn censuses of rabbits on the Kellogg areas have been conducted since 1950. Geis (1956) found large annual fluctuations of rabbit numbers and also fluctuations in fall populations of successive years. Geis also noted that the annual population fluctuations were independent of hunting pressure when he compared the heavily hunted populations of the Kellogg Forest with the lightly hunted populations of the Kellogg Bird Sanctuary. Kaczynski (1957), working on the same areas, was unable to find any correlation between fall population differences of consecutive years and the variations of weather patterns of these same years. In Iowa, Klein and.Henderson (1953) estimated that a _ 2 - f4 -3... cottontail (Sylvilagus floridanus) population declined from 284 rabbits, estimated on their area on October 1, 1952, to 41 on the same area on January 1, 1953. These workers ac- counted for 58 rabbits lost through hunting and predation but their general impression was that the observed decline was caused by reduction of food and cover brought on by the onset of cold weather. Lord (1960), working on two areas of equal size and vegetational composition, studied the possibility of food being a limiting factor in cottontail rabbit populations of central Illinois. He fed commercial rabbit food to the rabb? its on one of his study areas in alternate years and found that mortality rates in both populations were high and equal despite the extra food given to one population. No differences in average body-weights were found between the populations and Lord concluded that the lack of food was neither a direct nor an indirect cause of rabbit mortality on his study areas. ‘Parasites as direct causes or predisposing factors in rabbit mortality Dalke (1943) observed that his penned rabbits occasion- ally suffered drastic weight reductions which he suspected were due to "hatching" of roundworm eggs and subsequent larval feeding and migration in the digestive tracts and viscera. A California study, to which Chandler (1955) av~i 0 referred, showed that rabbits were killed by experimental infestations with 60 to 80 adult female ticks. Chandler al- so stated that adult female ticks often cause paralysis of their hosts. The mechanism of this paralysis is not known but was believed to be a neurotoxic substance associated with the development of eggs in the female tick. The victims often recovered rapidly when the offending tick was removed. Geis (1957) found that warbles, the larvae of cuterebrid flies, caused decreased growth rates and occasional deaths in young oottontails. Ectoparasites may often be indirect causes of rabbit mortality through transmission of diseases. Chandler (1955) states that ectOparasites have often been shown to be vectors of bacterial, rickettsial, viral and protazoan diseases. ‘Yeatter and Thompson (1952) found that tickdvectored tularemia was most prevalent when cottontail rabbits were most abundant. It was also found that tularemia epizootics rapidly declined after the onset of freezing weather which hastened deaths of infected rabbits and caused a cessation of tick activity. Davis (1953) suspected that an insular cottontail population in Chesapeake Bay was drastically reduced by an outbreak of tickdvectored.spotted fever. Packed-cell volumes chosen to measure_parasite damage Since the most common and conspicuous ectoparasites of cottontails are ticks and fleas which are blood feeders, the writer attempted to assess the numbers per rabbit and to cor- - 5 _ relate the resulting values with the packed-cell volumes of the hosts. Wintrobe (1951) stated that the packed-cell vol- ume is directly related to the red blood-cell and hemoglobin levels of an animal. When blood is lost, as through bleeding or heavy arthropod feeding, the fluid portion (plasma) is re- placed.more quickly than the cellular elements (Guyton, 1959). Animals with abnormally low packed—cell volumes are said to be anemic while those with abnormally high levels are polycythemic (Guyton, 1959). There is considerable normal variation in this measurement but it was hoped that the ectoparasite damage to rabbits would be extensive enough for significant diff- erences to be seen. Sources of variation ingpacked-cell volumes Albritton (1952) gave a range of 33 to 50 per cent and a mean of 41.5 per cent for packed-cell volumes of normal domestic rabbits. Wintrobe (1951) stated that adults have higher packed-cell volumes than children, among humans. The larger, heavier individuals of most species tend to have the highest values among adults. Some diseases also cause abnormal packed-cell volume var- iation. Guyton (1959) stated that diseases, such as pneumonia, produce polycythemia through the reduction of alveolar surface in lung congestion. He explained that a compensatory mechan- ism of the body brings about an increase in red blood-cell production in response to decreased availability of oxygen. I. . t a 1 . o -.-. . v . According to Schwartz and Shook (1935) young domestic rabbits are very susceptible to pneumonia and hemorrhagic septicemia, lung congesting diseases which may well infect young cotton- tails under adverse weather conditions. METHODS AND TECHNIQUES Rabbit Trapping Wooden live traps, described by Geis (1956), were set almost continuously from July 1 to December 22, 1959. All rabbits captured were individually ear—tagged, weighed and examined for fleas, ticks and warbles. Records of tag- numbers, capture location, body weight, blood sample results and ectoparasite loads were kept for each captured rabbit. Of 138 rabbits captured in the course of the study, only 27 were recaptured. Trapping success was very low from July through September and improved only slightly during October and November. The low capture rate might, perhaps, be explained by the fact that31959 fall population estimates for rabbits on the Kellogg areas were the lowest in the ten years of census figures (Geis, Brooke, Kaczynski, and Tullar, 1951-1960). The rabbits which were available seemed unusually trap-shy. Of 93 rabbits handled in July, August, and September, only six adults were captured and none of these were recaptured. Ectoparasite Counting and Estimating Ectoparasites were collected from 15 live—trapped rabbits captured in April and May. These collections were counted and identified with the plates and descriptions from.Stannard and Pietsch (1958). Two tick species were found; the continental (Haemophysallis leporis:palustris) and the eastern rabbit tick _ 7 - ’l 1‘ -8- (Ixodes dentatus). The first was found on 10 and the latter on four of the 15 rabbits examined. Two species of fleas were also found; the common (Cediopsylla simplex) and the giant rabbit flea (Odontopsylla multispinosus). These two species appeared to share their hosts with the former flea occupying the head and front quarters and the latter species the hind quarters. On two occasions in April, fleas were found feeding on the edges of the ears of several rabbits so tenaciously that one flea could be taken from a closely packed row without disturbing the fleas feeding on either side of it. In order to preserve the host—parasite relationship in anticipation of repeated observations, ticks and fleas were not removed from rabbits for counting and identification. Engorged ticks were counted ig;§itg on hosts and only presence or absence of unengorged individuals was recorded because of the difficulty in estimating their numbers. When found, six- legged ticks were identified as larvae and eight-legged forms were identified as nymphs or adults, a combined class. The latter stages were not separated because the distinguishing criterion is based in part on the gential opening (Chandler, 1955) which requires microscopic examination not practical in the field. It was suspected, late in October, that the writer may have overlooked engorged ticks attached to the inner hind legs of rabbits examined earlier in the season. .l o . u , v 4 “-- 1 » ‘-.. -9- Consequently, only the presence or absence of engorged ticks involved in infestations are recorded in the monthly distri- butions (Figure 1.). Estimates of flea-numbers per rabbit were made by count- ing the fleas seen after rubbing each side of a rabbit held in a cloth sack. This treatment caused fleas to move to the surface of the fur where they were counted. However, fleas quickly left the surface or moved rapidly back into the fur and the resulting numbers could only be used as index values. Counts from one to 19 were called "light" infestations, those from 20 to 39 were termed "moderate" and those over 40 fleas were listed as "heavy". The resulting flea-load indices were also applied to the counts of fleas obtained from the April and May ectoparasite collection and are recorded in the monthly distributions of flea infestations (Figure 2). Occurrence of Endoparasites Throughout the study 87 collections of droppings were taken directly from the anus of each rabbit or from.the traps in which they were captured. The feces were put in vials, covered with tapdwater and refrigerated at temperatures slightly above freezing. Later, the feces were stirred into aqueous suspension and studied using the heliminth flotation technique of Meyer and Penner (1958). Only the presence or absence of roundworm eggs or coccidian (Eimeria spp.) oocysts were recorded. Since 80 per cent of the samples contained .qn“ PERCDI‘ITAGES OF RABBITS INFESTED 100 --1 -10... 90— l 80" J 60“ 50" 1 4o 4 30“ 20-! ‘ \\\\\\\\\\\\\\\\L -'\\\\\\\\\\\\\\\\\l - * fc' .p y, APRIL MAY JULY AUG. SEPT. OCT. NOV. DEC. SAMPLE: 14 8 36 35 22 74 27 24 LEDGEND: Rabbits with r Rabbits with Rabbits - unengorged a engorged and with ticks unengorged ' engorged ticks ticks Figure 1. Monthly distributions of tick infestations on cottontail rabbits at Kellogg Bird Sanctuary and Forest, Kalamazoo County, Michigan, 1959 3 1 r—C? O '7 mfl/fl/fl/fl/fl I " .W‘ ‘ "91": u- .'.‘-'.1 . . _ :L__v O \ ' - OI- . .’ l. .L~. , . .. . .".i. "I ,) .d .3 3 'r L 94.x“..v I s ‘ r, . ." L.) A- . '34. n c -. , ‘. - _¢ ‘- ( s' .‘ . ‘1 l . ‘ u o- 1 -\ U ,5. 1». . TC’T' r‘ 5 0‘. LA‘h‘su a l'.’ -” d \ 4 ' I ‘ Ll \ 1‘ 5.3 as.) V a O ; ‘ 1 .J .‘ 3 L4 :.-k,;\‘.| (‘1‘. a X ' . - g ' ‘ l l a - ")L_' h . L 5‘ \ 5 ‘ ‘ .‘t” ‘1 l " .‘3 w-w . ‘ m ‘s. ‘I '! ) O 4 o 4 J- o - 5) u i 4.1 u c I (.3 A\’-‘- c I A u 0 r . . . ;- .r-- ,..,.e4 o .L. V .‘ I a. .. o- . ' ..;.\ \ - . s III 4.1 ‘ a u "' o ' ‘ ‘_ I ‘ o ‘ ‘r c l 1 .'n f "_ ‘ ‘ - b .. u ‘ a x .— - l ‘ - -..‘J n » -, ... ,.-' -' 0‘.- r' | " - . \: :v'r ' .e' ‘old‘ ‘ . t .1 - ' - . -01 I GAL} I .. RABBITS INFESTED M TAGE OF TH)“ T I. T“ A4 PERC 100 90 8O 7O 6O 5O 4O 3O 20 1O APRIL MAY JULY. AUG.. SEPT. OCT... NOV. DEC. , Light ‘ Moderate Heavy LEDGEND. E Infestations. Infestations-Infestations Figure 2. Monthly distributions of flea-loads of cotton- tail rabbits at W.K. Kellogg Bird Sanctuary and Forest, Kalamazoo County, Michigan Vtt!‘ I: III '0 5‘ ‘ ‘1‘ . . . . .Livl’ I I pull D . 5 r- h -0 '.H|| ' . 8 r fl A” l'. s I 8. 1‘ I all. A. 4 \5 \W... .‘II\ 1&- .trb . J r C F. ... O C C C C C O P - ._\ V o- 1- '- ‘0 h..\ 5.8—. n,- I“ fi‘ '4 o. ’4 .Ju. . I — .tJ . . a r... ... c A . v n t-‘~: .o' a .55.. J .c Tail. - 12 _ roundworm eggs and all samples contained oocysts, these parasites were considered to be common to all rabbits examined. Warbles (Cuterebra sp.) were found in 16.5 per cent of the rabbits handled during July, August and September and a few occurred as late as October 15. These fly larvae were usually found on the upper sterna of host rabbits but one was found in the rump and two were found over scapulae. Warbles are difficult to detect until the size of kidney beans (Geis, 1957) and were probably more common than observed. Swellings on rabbits were identified as warbles only if draining open- ings were found over them. Hemoflagellates (Trypanosoma sp.) were found in the blood smears of five rabbits in July. Two hundred and five smears were examined but these were the only rabbits found harboring these protazoans. Packed-cell Volume Determination One hundred and seventy-five samples of rabbit blood were used for determining packed-cell volumes. Blood was collected in heparinized capillary tubes (supplied by American Hospital Supply Corporation, Evanston, Illinois) from.punc- tures of marginal ear-veins of the rabbits. The tubes were sealed at one end with plastic putty and were carried to the laboratory in the flutes of corrugated cardboard. There, the tubes of blood were spun in a clinical centrifuge for ten minutes at maximum.speed (3800 to 4200 r.p.m.). The packed- ’. I oar-- - - v on; I 1 o 5 , _ 13 _ cell volume was determined by dividing the height of the resulting column of packed cells by the height of the total column of cells and plasma. According to Wintrobe (1951) there are several ways of expressing this ratio. The values presented are percentages, the packed-cell fraction multiplied by 100. Field use of capillary tubes was hindered by temperature extremes. Several samples were lost during hot weather when the cells were broken down after several hours at temperatures over 800 F. This hemolysis was prevented thereafter by carry— ing the filled tubes in a precooled, dry vacuum bottle. Freezing quickly caused complete hemolysis of all the red blood cells in the collected sample but was easily prevented in cold weather by carrying the tubes in an inside shirt pocket. RESULTS AND DISCUSSION Packed-cell volume variation related to age and season oijgag The general rise in halfsmonth packed-cell volume means, observed in the course of study (Figure 3). was found to be statistically significant. This increase might have been explained as being caused by the maturing of the large numbers of young rabbits in the 1959 fall Kellogg rabbit populations. To test for possible differences in packed-cell volume being connected with age, three age groups identified by bodydweight were chosen from rabbits captured in July and August. Those weighing less than 20 ounces were called infants, those over 25 ounces but not sexually mature (Petrides, 1951) were called juveniles, and adults were identified by ear-tags from.preyious seasons or by sex organ development. A statistical compari— son of the packed-cell volume distributions of these three groups gave no reason to suspect that the mean value of anymage— class was significantly different from.any other. Furthermore, while not significant, the packed-cell volume mean of the infant class was slightly greater than that of the adult class. When plotted together (Figure 4), an inverse relationship was observed between the half-month means of packed-cell volume distributions and the half-month means of daily minimum tempera- tures. The coefficient of correlation is -.946, which is valid at the .99 Per cent level of significance. This suggests that environmental temperatures may have a direct or indirect - l4 _ t 4 a a . . . . 1 . 1 .4 . . . . . . ¢ . r l s '\ . . J L. . . . b . . .. r k '\ . _ a h g a _ I Q s . U . x 1 _ I A, - . . L , o . n 4. u \| l a . I O . _ on U . \ P\ . Q . . c ‘ . . . Px , O u . . . I . _ . . . _ v \/ . , . a r a I _ l.\ .\ . U) S 3583 . 556.. so . E54. ' ' . ' 9452-! Q . : . a. o O:’ 50" .0 . 000: no: .. .;;--g;: I”’ 484 E o : o - 0:: oo--...:-’,’ 0 yo’ 0 ° 5- ‘ 3 - ' 13 -.°»""'”:‘: : . >4 O. ,«000: O. ’,”’ .3 o. O 5 :3- ‘ «Q '5" “0“; ’0” ..: Co .: _ .Q.‘ .Q 'o ",O F11 d O. 00.: z '5' 0.. .. (I43 0 . : o o: . .. o 36- . . .0: 5134‘ : 32- 304> . l l l l l A L A I L l J _J l I I I I I I I I I I I I 15 31 15 31 15 3O 15 31 15 30 15 31 JULY AUGUST SEPTHIIBER OCTOBER NOVEMBER DECEMBER Figure 3. Monthly distributions of packed-cell volumes of live-trap- ped cottontail rabbits at the Kellogg Bird Sanctuary and Forest, Kalamazoo County, Michigan Each dot represents a packed-cell volume determination for a single rabbit, the curve indicates the fluctuation of the half-month distribution means. f @- h i. ‘ ‘ s .5. » ‘. . ‘ I\ ‘ ) .. ‘ - . , I '1 ‘ ' A 0' a» _ '\ . I .3 -‘ “ 0 ' |‘ J a ' d -<-— - . - . - g r A ~ ‘4 v 6 .- ' ‘ ' ‘ . . - .' l _ I _ I I d ‘ , ~ . K a: \. ’_.‘ Inn-"M PACKED-CELL VOLULE PERCENTAGES [-65 / P60 Means of daily - ? minimum temperature -55 6O -1 I -sgr-I ' .‘3 55 ‘ 45% 50 '1 1’. 1'40; ".~~‘~ ” m ----e” . 45 - .5 ~35§ " ‘ ,0 fi.‘- ”' ‘\ a’J '0 4O “ 'k'Packed-cell volume '30 means 20 30 I l l I 15 I1 15 I1 15 50 15 51 '15 30 1'5 31 JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER Figure 4. The relationship between packed-cell volume means of cottontail rabbits and the means of daily minimum atmospheric temperature. The temperature data are from the meteorological re- cords of the W.K. Kellogg Forest, Kalamazoo County, Michigan. .I s lb- 4 It . 1: Cf - 17 - effect upon the packed-cell volumes of rabbits, a phenomon which should be further investigated if rabbit blood values are to be compared from different seasons. Packed-cell volume variation associated with_parasites The packed-cell volume distribution of 10 rabbits infected with warbles was compared with that of 35 rabbits which had no detectable warbles. Neither group contained rabbits infested with engorged ticks nor any having flea-loads heavier than "light". A ”t" test gave no reason to suspect that the packed- cell volume distributions of the two groups were significantly different. The packed-cell volume distributions of five rabbits harboring hemoflagellates and nine chosen at random from the uninfected group were compared statistically. There were no significant differences between the means or the variances of the two groups distribution. Group comparisons were not possible for comparing tick- infested with tick-free rabbits because of the very low inci- dence of engorged ticks on rabbits from.which packed-cell determinations were made. However, among rabbits captured three or more times, two young ones (ear-tag numbers 463-466 and 403-404, Appendix) which had the lowest packed—cell volumes were also infested with ticks when blood was collected. It generally appears among the recaptured rabbits recorded, that young rabbits with histories of tick infestations show (h I‘d - 18 - more variable packed-cell volume patterns than those on which ticks were not found. However, the differences in time inter- vals between captures of different rabbits do not make this a valid conclusion. Flea-loads of rabbits captured during October ranged from none to “moderate“. Two groups of rabbits at the extremes of the index were six moderately infested and nine rabbits unin- fested with fleas. The packed-cell. volume means of the two groups were 44.1 and 48.7 per cent, respectively. However, a "t" test gave no reason to believe that the observed difference between the means of the two groups was significant. Discussion This study has shown that the packed—cell volumes of cottontail rabbits appear to vary inversly with minimum at- mospheric temperature but do not seem affected by maturation or increase in bodydweight. Warbles and hemoflagellates did not appear to affect packed-cell volumes. While Geis (1957) found that warbles caused significant increases in white blood cell numbers it does not seem inconsistant that no packed-cell volume increase was found in this study. This is because the ratio of white to red blood cells is 1:500 (Guyton, 1959) and even a ten-fold increase would hardly be noticed in the total volume of cells. However, I did find a small white layer overlying the red cell column at the cell—plasma interface in several centrifuged tubes. This white material (presumably _¢ u u n . . I -3. \ «. u~ .v I .i I u _ 19 _ white cells) was too thin to measure but is said to be a fair measure of white cell numbers by Wintrobe (1951) when larger hematocrit tubes (1 cc.) are used. Tick and flea infestations appeared to cause small var- iations in rabbit packed-cell volumes but the evidence pre- sented is not conclusive in either case. The greatest problem of this study was in finding large contrasts in infestation levels. While tick and flea infestations appeared to be exceptionally heavy during April and May of 1959, blood samples could not be treated. Other factors such as lung diseases, roundworms and coccidia are difficult to measure and may increase or decrease packed—cell volumes only under certain conditions. However, I do think that it is possible to use blood to demon- strate that ectoparasites constitute stresses which may bring about reproductive difficulty and even deaths of parasitized rabbits. Because it is difficult to capture uninfested rabbits for comparisons when infested rabbits are available, I think it would he more convenient and rewarding to confine rabbits to cages or small pens where they could be experimentally infest- ed and easily captured. This would enable the worker to establish the extent of enviromental influences, such as tem- perature, which might make the effects of parasitism difficult to interpret. A further consideration should also be made where the I. technique of blood analysis is concerned. It is possible to take four to five cubic centimeters of blood by heart-punct- ures of rabbits without killing them. This method allows a much larger sample from which determinations of blood sugar, proteins and lipids may also be made. I think it is important that the physiological influence of parasites be known in order to assess the role in which they might play in the fluctuations of rabbit populations. SUMMARY Data were collected concerning the incidence of warbles, hemoflagellates, coccidians, ticks and fleas harbored by cottontail rabbits on the Kellogg Bird Sanctuary and Forest, Kalamazoo County, Michigan. In an effort to determine the status of these parasites as possible limiting factors of rabbit populations, packed-cell volumes were determined for most of the rabbits captured from July 1 to December 22, 1959 in order to study the effects of parasites on the animals. Extremes of means and ranges of packed-cell volumes were determined by analyses of half—month distributions. It was found that the packed-cell volume means of rabbits taken in July and August were significantly lower than those taken in October, November and December. Statistical‘ analyses of the packed-cell volume distributions of infant, juvenile and adult rabbits showed no significant differences attributable to age or body—weight. However, an inverse relationship was found between rabbit packed—cell volume means and means of daily minimum atmospheric temperature. This relationship was found to have a correlation coefficient of - .946, which is highly significant. Comparisons of packed-cell volume distributions of groups of rabbits harboring warbles, hemoflagellates and fleas were made with groups found to be free of these parasites. The _21_. Is\ eu\ -22.. results indicate that warbles and hemoflagellates produced no differences in red blood cell levels. While some evidence indicated that ticks and fleas caused decreases in red blood cell numbers. This evidence was either inconclusive or insignificant. LITERATURE CITED Albritton, E.C. 1952. Standard values in blood. W.B. Saunders. Philadelphia and London. 199 pp. Chandler, A.C. 1955. Introduction to parasitology. John Wiley and Sons. New York. 799PP. Dalke, P.D. 1942. The cottontail rabbits of Connecticut. State of Conn. Public Document No. 47. Bull. No. 65. Davis, D. E. 1953. Studies on rabbits and spotted fever. Trans. 20th No A. Wildlo Conf. 170-1900 Geis, A.D., R. Brooke, C. Kaczynski and B.F. Tullar. 1951-1960. Unpublished notes and reports on.Kellogg area rabbits. Mich. State University. Geis, A.D. 1956. A population study of the cottontail rabbit in southern Michigan. Ph.D. Thesis. Mich. State Univ. . 1957. Incidence and effect of warbles on southern Michigan oottontails. J. Wildl. Mgmt., 21:94-95. Guyton, A.C. 1959. Function of the human body. W.B. Saunders. Philadelphia and London. 584pp. Kaczynski, C. 1957. Unpublished notes and reports. Mich. State University. Klein, P4D., and G.O. Henderson. 1953. Autumnal decimation of mearns cottontail, Decatur County, Iowa, 1952. Proc. Iowa Academy of Sci., Vol. 61. Lord, R.D., and D.A. Casteel. 196C. Importance of food to cottontail winter mortality. Trans. 25th N. A. Wildl. Conf 0 267-276 0 Meyer, M.C., and L.R. Penner. 1958. Laboratory essentials of animal parisitology. Wm.C. Brown Co. Dubuque, Iowa. 103pp. Petrides, G.A. 1951. The determination of sex and age ratios" in the cottontail rabbit. Amer. Midl. Nat. 46:2 312-336. Schwartz, B., and W.B. Shook. 1935. Rabbit parasites and diseases. Farmer‘s Bull. No. 1568. U.S.D.A. _ 23 _ NII". on IE»! —.-1‘r- .. .\ O O _ 24 - Stannard, L.J. and L.R. Pietsch. 1958. Ectoparasites of the cottontail rabbit in Lee county, Illinois. Ill. Nat. Hist. Survey Div. Biological note No. 38. Walker, H.M., and J. Lev. 1953. Statistical inference. Henry Holt, New York. 510pp. Wintrobe, M.M. 1951. Clinical hematology. Lea and Febiger. Philadelphia. 1048pp. Yeatter, R.E., and D.H. Thompson. 1952. Tularemia, weather and rabbit populations. Bull. Ill. Nat. Hist. Survey Div. 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