University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln

USGS Northern Prairie Wildlife Research Center US Geological Survey

1981

Determination of Age and Whelping Dates of Live Red Fox pups

Alan B. Sargeant USGS Northern Prairie Wildlife Research Center

Stephen H. Allen USGS Northern Prairie Wildlife Research Center

Douglas H. Johnson USGS Northern Prairie Wildlife Research Center, [email protected]

Follow this and additional works at: https://digitalcommons.unl.edu/usgsnpwrc

Part of the Other International and Area Studies Commons

Sargeant, Alan B.; Allen, Stephen H.; and Johnson, Douglas H., "Determination of Age and Whelping Dates of Live Red Fox pups" (1981). USGS Northern Prairie Wildlife Research Center. 213. https://digitalcommons.unl.edu/usgsnpwrc/213

This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Northern Prairie Wildlife Research Center by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 760 SHORT COMMUNICATIONS field observations, and R. D. Eliason, J. LOTZE, J. H., AND S. ANDERSON. 1979. Procyon lotor. Mamm. 119. D. Hilley, and J. O. Hastings assisted in Species 8pp. MECH, L. D., D. M. BARNES, AND J. R. TESTER. the field, B. A. Hanson assisted with fecal 1968. Seasonal weight changes, mortality, and analysis, and D. A. Davenport and D. H. population structure of raccoons in Minnesota. Mammal. 49:63-73. Johnson assisted with data analysis. C. J. SCHNEIDER,D. G., L. D. MECH, AND J. R. TESTER. Scholl, North Dakota Department of Ag- 1971. Movements of female raccoons and their riculture, and A. S. Menke, USDA, Agri- young as determined by radio-tracking. Anim. Behav. 4:1-43. cultural Research Center, Beltsville, SCHOONOVER, L. J., AND W. H. MARSHALL. 1951. Maryland, identified some of the insects. Food habits of the raccoon (Procyon lotor hir- tus) in north-central Minnesota. J. Mammal. LITERATURE CITED 32:422-428. SCOTT, T. G. 1941. Methods and computation in W. F. 1973. and life of COWAN, Ecology history fecal analysis with reference to the red fox. the raccoon Nelson (Procyon lotor hirtus and Iowa State J. Sci. 15:279-285. in the northern of its Goldman) part range. STAINS, H. J. 1956. The raccoon in Kansas, natural Ph.D. Thesis. Univ. North Grand Dakota, history, management, and economic impor- Forks. 161pp. tance. Univ. Kansas, Lawrence, State Biol. Surv. E. K. 1978a. Habitat use rac- FRITZELL, by prairie Misc. Publ. 10. 76pp. coons the waterfowl season. during breeding J. STEWART, R. E. 1975. Breeding birds of North Wildl. 42:118-127. Manage. Dakota. Tri-Coll. Cent. Environ. Stud., Fargo, . 1978b. of raccoon Aspects (Procyon lotor) N.D. 295pp. social organization. Can. J. Zool. 56:260-271. ,AND H. A. KANTRUD. 1971. Classification R. 1979. residue in GREENWOOD, J. Relating rac- of natural ponds and lakes in the glaciated prai- coon feces to food consumed. Am. Midl. Nat. rie region. U.S. Fish and Wildl. Serv., Resour. 102:191-193. Publ. 92. 57pp. A. S. 1970. of the raccoon JOHNSON, Biology (Pro- ,AND . 1974. Breeding waterfowl pop- lotor varius Nelson and in cyon Goldman) Al- ulations in the prairie pothole region of North abama. Auburn Univ. Agric. Exp. Stn. Bull. 402. Dakota. Condor 76:70-79. 148pp. STOUDT, J. H. 1971. Ecological factors affecting L. 1971. behavior of KILHAM, Reproductive yel- waterfowl production in the Saskatchewan low-bellied sapsuckers. I. Preference for nest- Parklands. U.S. Fish and Wildl. Serv., Resour. in Fomes-infected and nest hole in- ing aspens Publ. 99. 58pp. terrelations with and flying squirrels, raccoons, WELCH, P. S. 1948. Limnological methods. Mc- other animals. Wilson Bull. 83:159-171. Graw-Hill Co., Inc., New York, N.Y. 381pp. KRAPU, G. L. 1978. Productivity of red-winged blackbirds in prairie pothole habitat. Iowa Bird Received 31 March 1980. Life 48:24-30. Accepted 30 September 1980. LLEWELLYN,L. M., AND C. G. WEBSTER. 1960. Raccoon predation on waterfowl. Trans. North Am. Wildl. and Nat. Resour. Conf. 25:180-185.

DETERMINATION OF AGE AND WHELPING DATES OF LIVE RED FOX PUPS

ALANB. SARGEANT,Northern Prairie Wildlife Research red foxes (Vulpes vulpes). A technique Center,Jamestown, ND 58401; STEPHENH. ALLEN,North Dakota Game and Fish Department,Bismarck, ND 58501; for assigning individuals to age-classes is and DOUGLASH. JOHNSON,Northern Prairie Wildlife Re- necessary to understand the population search Center, Jamestown, ND 58401. dynamics and behavioral interactions of Public concern for large carnivores, this species. Previous studies have fo- high longhair fur prices, and recent find- cused on separating young from adults ings of predator-prey investigations have and on estimating age of adults (Harris increased interest in the management of 1978), but a need exists to know age of

J. Wildl. Manage. 45(3):1981 SHORT COMMUNICATIONS 761 live pups. Pup age data can be used to The 2nd data set involved 900 pups ascertain conception and whelping dates captured during April through July 1969- and age-specific behavior at dens. Age of 73 at 260 rearing dens. Most dens were captured live pups can be estimated from found during annual mid-May and mid- morphological changes (Linhart 1968), June systematic aerial searches of 6 93- hind-foot length (Johnson et al. 1975), zy- km2 study areas (Sargeant et al. 1975). We gomatic breadth (Storm et al. 1976), and measured the length of the right hind foot body weight (Sargeant 1978). These of each pup and recorded pelage color methods are not widely used and, except and body size. These pups provided the for hind-foot length, their accuracy has data for establishing relationships be- not been documented. Methods that tween estimated age (based on hind-foot avoid capturing pups would be particu- length) and pelage color and body size. larly useful in some studies, but none is The 3rd data set consisted of observa- available. In this paper we evaluate the tions of pelage color and body size of one use of hind-foot length, pelage color, and or more pups at 764 dens (including the body size for estimating the age of red fox 260 dens mentioned above) in Iowa, pups, and apply these criteria to deter- North Dakota, and South Dakota that mine whelping dates of red foxes in the were visited by us or by cooperators. The northern Great Plains. Iowa dens were the same dens reported by Storm et al. (1976). North and South METHODS AND STUDY AREAS Dakota were stratified into areas east and We used 3 data sets: (1) measure- west of the Missouri River. Survey par- ments obtained during 1969-71 of pen- ticipants were asked to select 1 of 5 color reared pups held captive in outdoor pens and 1 of 7 size categories that best de- at the Northern Prairie Wildlife Research scribed the pup(s) seen at each den. Center, Jamestown, North Dakota, or out- Whelping dates were calculated by doors at the Dakota Zoo, Bismarck, North first establishing the age of each litter Dakota; (2) measurements obtained dur- from the average estimated age of all lit- ing 1969-73 of pups captured at natural termates determined from hind-foot dens in eastern North Dakota, primarily length or from a description of pelage col- in Barnes, Kidder and Stutsman counties; or and body size, and then subtracting and (3) visual observations made during that age from the date of capture. 1969-70 of wild pups at numerous dens in Iowa, North Dakota, and South Dako- RESULTS ta. Hind-foot The captive foxes were 28 wild-caught Length Age Determination pups obtained at 5-8 weeks of age and Johnson et al. (1975) found that hind- fed simulated natural diets, and 9 known- foot length was excellent for estimating age pups born in captivity. Hind-foot age of pups to about 80 days of age (Table length, pelage color, and body size (rel- 1), but that the reliability of this criterion ative to adults) were recorded at weekly was questionable for older animals. intervals. Equations for estimating age Hind-foot lengths of newborn red foxes from hind-foot length were developed were nearly identical between sexes and from these data (Johnson et al. 1975). similar among regions: 29 mm among 6 These equations require mean hind-foot newborn foxes in North Dakota (this lengths at both birth and maturity. study); 28 mm among 21 full-term fetuses

J. Wildl. Manage. 45(3):1981 762 SHORT COMMUNICATIONS

Table 1. Estimated age of male and female red fox pups scribed by Linhart (1968). From birth to based on length of hind foot (from Johnson et al. 1975). 14 weeks the pups exhibited 3 distinct Estimated age (days) color phases: dark gray, pale buff, and Hind-footlength (mm) Male Female red. In addition, there were 2 interme- 1 each in the transitions 30 1.3 1.7 diate phases, 40 9.5 10.1 from gray to buff and from buff to red. 50 16.5 17.3 Thus, we categorized the 5 color phases 60 22.9 23.9 70 28.9 30.1 as gray, gray-brown, buff, buff-red, and 80 34.7 36.2 red. 90 40.5 42.4 Seventy-six captive and wild North 100 46.5 48.9 110 52.8 55.9 Dakota pups were classed as gray; the 120 59.7 63.7 oldest was 40 days old. Pups cannot walk 130 67.5 73.1 until about 3 weeks old (Linhart 1968), 140 76.9 85.2 and observations of our captive foxes in- dicated that they did not spend time out- side dens until they were 4-5 weeks old. in New York (Layne and McKeon 1956); Thus, most gray pups seen outside dens and 29 mm among 18 full-term fetuses in are 28-40 days old. The color change Illinois and Wisconsin (Storm and Ables from gray to buff was completed in less 1966). On the other hand, sexual dimor- than 2 weeks. The average age of 119 phism affects hind-foot length at an early gray-brown pups was 40 days (range 35- age (Table 1), and asymptotic hind-foot 60 days). Pups remained buff colored for length varies among regions (McIntosh about 3 weeks and then gradually be- 1963, Fairley 1970, Storm et al. 1976). came red as guard hairs appeared and the Mean asymptotic hind-foot lengths of 116 woolly puppy appearance was replaced male and 85 female adult foxes, trapped by the sleek adult look. Buff- and buff- or hunter-shot in North Dakota, were red-colored pups averaged 49 and 69 169.9 mm (SD = 6.1) for males and 161.5 days old, respectively. The youngest red mm (SD = 5.2) for females. pup was 61 days old. Because adult foxes There was little variation in growth also are red, this color phase is only use- rates among siblings, hence determined ful to establish that pups are a minimum age of a single pup is a fairly accurate age or older. measurement of age of the litter. We ex- Visual estimates of pup body size are amined 142 litters with 3 or more pups, subjective; therefore, we used this crite- and 81% had a within-litter standard de- rion primarily to confirm the accuracy of viation in estimated age of 4.0 days or the pelage color descriptions and to in- less. Six litters with greatest spread of dicate possible growth abnormalities. We pup ages had standard deviations of 9.1- established 7 size categories: 1/8, /4, 1/3, /2, 15.0 days. We believe that each of these 2/3, 3/4, and full grown. 6 litters included pups of 2 vixens sharing Six of the 35 possible pelage color- the same den, as communal dens are body size descriptions accounted for 88% common among red foxes (Sheldon 1950, of the pups handled at dens in eastern Storm et al. 1976). North Dakota (Fig. 1). These were the only descriptions subsequently consid- Visual Age Determination ered for use in estimating age, which re- Pelage color changes among our pen- stricted analysis to easily distinguishable reared pups were similar to those de- color-size descriptions and resulted in J. Wildl. Manage. 45(3):1981 . =

SHORT COMMUNICATIONS 763

20- RED 2/3 GROWN 10-

o ,,,, ^,1-.,.,,, ,. . cr:10 RED Il III | 1/2 GROWN 10- LL i 5 O0- ,. ,I'v. ., .. , , , , O UL] 5 BUFF-RED V) Q20- 2 n 1- 1/3 GROWN L 2 a- 10- LL O . .. .- 0 ...... Ill 1 I1 MAY w 20- MARCH APRIL m 30- BUFF DATE 2 20- 1/4 GROWN z Fig. 2. Whelping dates of red fox litters, 80 days old or 10- younger, caught at 207 dens in eastern North Dakota dur- ing 1969-73. The mean whelping date was 31 March.

GRAY-BROWN 20- 1/4 GROWN March to 1 May (58 days) and averaged 10- 31 March (Fig. 2). Mean annual -6 whelping 0 , , , " . . GRAY dates for each of the 5 years ranged from 10- j 1/8 GROWN 28 March to 1 April. 0 .-II...i 10 30 50 70 90 lio 150 150 From observations of pelage color and AGE (DAYS) body size, we were able to estimate mean Fig. 1. Relationship of 6 most commonly used descrip- whelping dates of pups from the 5 areas tions of red fox pup pelage color-body size to age of the in pups estimated from hind-foot length. Iowa and North and South Dakota for 1969-70. Only pups in the 3 intermediate color-size categories were used in the excluding atypical pups. Three of these calculations, which included 40% of the age-classes, however, involved small observations of pups. The mean whelp- gray or large red pups and were inade- ing dates of foxes in Iowa and both east- quately sampled or open-ended. There- ern and western South Dakota were near- fore, we could most accurately estimate ly the same (16, 14, and 14 March, age only from the 3 intermediate cate- respectively). The mean whelping dates gories: gray-brown--1/4 grown, buff-1/4 of foxes in eastern and western North grown, and buff-red--/3 grown. Two of Dakota were 2 and 3 April, which are these involved pups of about the same similar to results based on hind-foot size, but with easily distinguished pelage length. colors. Mean ages of pups in these 3 cat- DISCUSSION egories were 43, 53, and 69 days old, re- spectively. An obvious advantage to estimating age from hind-foot length or visual ob- Determination of Dates Whelping servations of pelage color and body size Whelping dates can be established by is that it can be done without harming the back-dating pup age from date of capture. foxes. The hind-foot method is particu- Whelping dates of eastern North Dakota larly accurate for determining age of pups red foxes during 1969-73 based on hind- up to 80 days old (Johnson et al. 1975). foot lengths of pups from litters with The hind foot is easily measured and its mean age 80 days or less ranged from 3 rapid daily growth (about 1.4 mm/day) re- J. Wildl. Manage. 45(3):1981 764 SHORT COMMUNICATIONS duces effects of small measurement itude and climate. Mean whelping dates errors. The visual method of estimating of the foxes in Iowa and South Dakota pup age, although less accurate than the were similar to each other, but about 18 hind-foot method, is well suited to stud- days earlier than in North Dakota. ies in which dens cannot be disturbed, or The only comparative data on whelp- to extensive or long-term surveys. For ing dates in the regions studied are pro- use in establishing whelping dates, rela- vided by Storm et al. (1976). These in- tively large numbers of observations vestigators independently estimated should be made, and sampling should conception dates for the same Iowa foxes span the dates when pups of a particular used in the present study on the basis of color-size group can be observed. The zygomatic breadth, and concluded that spread of whelping dates in eastern the peak of conception occurred during North Dakota indicates this is about a 2- 17-24 January and ranged from early De- month period. cember to mid-February. By adding 52 Several factors affect application of our days for gestation (Asdell 1964), the peak methods. Fox size varies geographically, of whelping would have occurred from and therefore mean adult hind-foot 10 to 17 March, which encompasses our lengths should be determined for each estimate of 16 March based on pelage area in which the hind-foot age determi- color and body size. Further, their wide nation equations are to be applied. Pel- range of conception dates is similar to the age color of adult foxes also varies among range in whelping dates that we found regions. The clearly defined gray-brown for eastern North Dakota. and buff categories of most prairie foxes Acknowledgments.-We appreciate the will likely require different interpreta- assistance of individuals from the U.S. tion in regions with darker foxes. Finally, Fish and Wildlife Service; Iowa Conser- the exclusion from data sets of obviously vation Commission; North Dakota Game aberrant pups or of seldom-used color- and Fish Department; South Dakota De- size categories will improve the accuracy partment of Game, Fish and Parks; and of dating reproductive or behavioral University of Minnesota, who cooperated events. in the den questionnaire survey. We Breeding and whelping chronologies thank D. T. Allen, R. T. Eberhardt, E. K. of wild red foxes are only generally Fritzell, T. C. Hendrickson, W. H. How- known because most estimates are based ell, R. E. Nelson, W. K. Pfeifer, G. L. on chance observation of breeding or Rohde, and J. F. Wolf, who assisted in whelping. The whelping dates we esti- locating fox dens in eastern North Dakota mated from fox hind-foot lengths in east- and who helped obtain pups for exami- ern North Dakota show that pups were nation, and R. J. Greenwood for manu- born from early March to late April. The script review. extreme dates, however, may reflect small errors in estimating age of individ- LITERATURE CITED ual pups. The mean whelping date varied S. A. 1964. Patterns of mammalian 5 the 5 studied. ASDELL, repro- only days among years duction. Cornell Univ. Press, Ithaca, N.Y. Our visual methods provided results sim- 670pp. ilar to the hind-foot method, and verify FAIRLEY, J. S. 1970. The food, reproduction, form, differences in dates of foxes in growth and development of the fox (Vulpes whelping vulpes L.) in northeast Ireland. Proc. Royal nearby regions that may be related to lat- Irish Acad. 69:B103-B 137.

J. Wildl. Manage. 45(3):1981 SHORT COMMUNICATIONS 765

HARRIS, S. 1978. Age determination in the red fox ,W. K. PFEIFER, AND S. H. ALLEN. 1975. A (Vulpes vulpes)-An evaluation of technique spring aerial census of red foxes in North Da- efficiency as applied to a sample of suburban kota. J. Wildl. Manage. 39:30-39. foxes. J. Zool. Lond. 184:91-117. SHELDON, W. 1950. Denning habits and home JOHNSON,D. H., A. B. SARGEANT,AND S. H. ALLEN. range of red foxes in New York state. J. Wildl. 1975. Fitting Richards' curve to data of diverse Manage. 14:33-42. origins. Growth 39:315-330. STORM, G. L., AND E. D. ABLES. 1966. Notes on LAYNE, J. N., AND W. H. MCKEON. 1956. Notes on newborn and full-term wild red foxes. J. Mam- the development of the red fox fetus. N.Y. Fish mal. 47:116-118. and Game J. 3:120-128. , R. D. ANDREWS,R. L. PHILLIPS,R. A. BISH- LINHART, S. B. 1968. Dentition and pelage in the OP, D. B. SINIFF, AND J. R. TESTER. 1976. juvenile red fox (Vulpes vulpes). J. Mammal. Morphology, reproduction, dispersal, and mor- 49:526-528. tality of midwestern red fox populations. Wildl. MCINTOSH, D. L. 1963. Reproduction and growth Monogr. 49. 82pp. of the fox in the Canberra District. CSIRO Wildl. Res. 8:132-141. Received 11 April 1980. SARGEANT, A. B. 1978. Red fox prey demands and Accepted September 1980. implications to prairie duck production. J. Wildl. Manage. 42:520-527.

DIAMETER AND pH COMPARISONS OF COYOTE AND RED FOX SCATS

JEFFREYS. GREEN1and JERRANT. FLINDERS,Botany between and within species may affect and Range Science Department, Brigham Young Univer- sity, Provo, UT 84602. fecal pH, the technique should be eval- uated for usefulness on a local basis. We of data obtained from fe- Interpretation found no publication of the application of cal the to iden- analysis presumes ability this technique to scats of carnivores. the animal that tify correctly produced Weaver and Fritts (1979) evaluated the the scat. This identification can be diffi- use of scat diameter to distinguish be- cult where related de- sympatric species tween feces of coyotes and wolves (Canis feces similar in We re- posit appearance. lupus). Application of this technique to an to scats from port attempt distinguish coyote and red fox scats would have val- and sympatric coyotes (Canis latrans) ue to biologists studying these canids in- red foxes in southeastern (Vulpes vulpes) dividually or in sympatry. Idaho with pH and diameter measure- ments. METHODS Fecal pH has been used to distinguish Scats were collected monthly on the between related herbivore species (How- U.S. Sheep Experiment Station, Dubois, ard 1967, Nagy and Gilbert 1968, Howard Idaho, from 1976 to March 1978, and De Lorenzo Krausman et al. January 1974, dirt roads. Over 28% of Hoff Hansen how- primarily along 1974, 1977). (1978), the 362 scats collected were deleted from ever, reported that using pH for this pur- the analysis due to questionable identi- pose was narrowly restrictive because of fication. Only scats that could be correct- the potential for highly variable values. ly identified as being red fox or coyote Peek and Keay (1979) suggested that be- were used. Scats were identified by ob- cause diet and physiological differences servation of associated tracks and prey kills in snow and by proximity to known of use. Present address: USDA, SEA-AR, U.S. Sheep dens and areas preferred Subse- Experiment Station, Dubois, ID 83423. quent analysis of the contents of the scats

J. Wildl. Manage. 45(3):1981