Denning Habits of Striped Skunks (Mephitis Mephitis) Author(S): Clyde R

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Denning Habits of Striped Skunks (Mephitis mephitis) Author(s): Clyde R. Houseknecht and John R. Tester Reviewed work(s): Source: American Midland Naturalist, Vol. 100, No. 2 (Oct., 1978), pp. 424-430 Published by: The University of Notre Dame Stable URL: http://www.jstor.org/stable/2424842 . Accessed: 08/02/2012 12:44

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http://www.jstor.org Denning Habits of Striped Skunks (Mephitis mephitis)

CLYDE R. HOUSEKNECHTi and JOHN R. TESTER

Bell Museum of Natural History, University of Minnesota, St. Paul 55101

Abstract: Thirty-six striped skunks were located in the field a total of 1627 times. There was a general shift from underground, upland dens in winter to aboveground, lowland dens in summer. Significant intraspecific contact occurred through concurrent and sequential use of underground dens and hollow logs. Den-sharing occurred only between the 3rd week in October and the 1st week in April. Both males and females changed den locations frequently. The average straight line distance between successive den sites was 0.48 km.

Introduction Several authors (Seiko, 1938; Allen, 1939; Allen and Shapton, 1942) have de- scribed aspects of the denning habits of striped skunks (Mephitis mephitis). However, before the development of radio telemetry, techniques did not permit observations on large numbers of skunks for extended periods of time, and, as a result, many studies were limited to few individuals during restricted periods of the year. Verts (1967) and Storm (1972) used radio telemetrie techniques to investigate den site selection of skunks in an intensively cultivated region in northern Illinois. This paper reports on the denning habits of striped skunks on an area of cultivated and abandoned farmland and second-growth woodland 30 miles ? of Minneapolis, Minnesota. * The objectives of this study were to determine: (1) the types of dens used relative to the physiographic and vegetative characteristics of the area, and ( 2 ) the frequency of use of different den types on a seasonal basis. In addition, because the striped skunk is a major reservoir of rabies (Verts, 1967) and leptospirosis (Roth et al., 1963), emphasis was placed on the effect of den-use patterns on the potential for intraspecific contact.

Study Area The topography of the study area (Cedar Greek Natural History Area) is flat to gently rolling with sandy upland areas interspersed with sedge (Carex spp. ) meadows, white cedar (Thuja occidentalis) and alder (Alnus rugosa) swamps, cattail (Typha latifolia) marshes, cultivated and abandoned cropland, two small lakes and a creek. Bray et al. (1959) classified the upland cover as mixed conifer-angiosperm forest, deciduous-angiosperm forest and tall-grass prairie. The predominant upland trees are oaks (Quercus ellipsoidalis, Q. macrocarpa, Q. alba, Q. rubra) and pines (Pinus resinosa, P. strobus), with scattered basswood (Tilia americana) and sugar maple (Acer saccharum) with a dense hazel (Corylus cornuta) understory. White cedar, tamarack (Larix laricina) and alder dominate the lowland forest with such asso- ciated species as red osier (Cornus stolonifera), willow (Salix spp.), white birch (Betula papyrifera) and aspen (Populus tremuloides). The principal cultivated crops are corn (Zea mays), soybeans (Lens esculenta), alfalfa (Me die ago sativa) and rye (Secale cereale). Rongstad and Tester (1969) subjectively categorized the 16 sq miles containing and surrounding the study area as 64% upland (23% woods, 41% fields) ; 32% lowland (18% marsh, 14% wooded swamp), and 4% open water. The normal length of the frostless season is mid-May to the end of September, Out in low areas no month can be presumed to be frost-free. The normal period of

1Present address: Wilkes College, Wilkes-Bajrre, Pennsylvania 18703. 424 1978 Houseknecht and Tester: Skunk Denning 425 snqw^ cover is about 30 November to 15 March. Mean annual precipitation is 67.6 cm. During the present study (October 1967 to November 1969) temperatures ranged from ??36 to 35 C with an average monthly maximum and minimum of 26 G (July and August) and"?30 C (January), respectively. Weather data were recorded at the U.S. Weather Bureau Station of Cedar Greek Natural History Area.

Methods Skunks were captured, anesthetized with ether, weighed, and the sex and age determined. Three capture methods were employed; live trapping in National-style box traps, excavation of dens, and live traps set in enclosures surrounding active den sites. Live traps were set at likely locations (primarily along a network of dirt roads within the study area) and were operated for 1 week each month. All newly captured skunks were tagged with radio-transmitter collars weighing about 75 g (Cochran and Lord, 1963; Mech et al., 1965) and were released where captured. Each transmitter operated on a different radio frequency. Animals were recaptured at approximately 5-month intervals to replace transmitter batteries. Two schedules of data collection were employed. Between 1 November 1967 and 7 March 1968, and between 15 November 1968 and 9 April 1969, each radio-tagged skunk was located, at least three times per week with the aid of a portable direction- finding receiver. During the remainder of the study we attempted to locate three randomly selected individuals each day, Monday through Friday. For this study 36 skunks were located in the field a total of 1627 times. Each den and aboveground rest site was marked with an identifying tag. On days when the actual locations of radio-marked skunks were not determined, approximate locations (relative to two stationary receiving towers) were obtained at 1100, 1200 and 1300 hr. If the bearings o? all three locations were within plus or minus Io, the skunk was assumed to be in a den or daytime rest site.

Results Two hundred and six dens and 183 aboveground rest sites were located during this study. Of 206 dens located, 147 (71%) were underground, 43 (21%) were in logs or trees and 16 (8%) were in junk piles or buildings. The high percentage of underground dens seemed to reflect a preference for that den type because many fallen trees, hollow logs and buildings were present but were not used by striped skunks that were radio-tracked in this study. There was a distinct seasonal shift in the types of dens used by striped skunks (Fig. 1 A, B). During the winter skunks of both sexes used underground dens almost exclusively, but after emergence from the winter dens both males and females began to use aboveground rest sites and hollow logs. Males continued to use these types throughout the spring and summer while females used underground dens during parturition and lactation. Winter dens were almost always in upland habitats = (x2 20.6, ? < .001) while a significant proportion of summer rest sites were in lowland areas. After the young began to travel with the female in late June and early July, both sexes used aboveground rest sites extensively. As winter approached, both sexes began to use underground dens with increasing frequency. The sharp deflection on the curve for females (Fig. 1 B) during May and June 1969 resulted from a female that apparently did not breed until about 28 April, ca. 2 months after the usual breeding season. This animal continued to use aboveground rest sites during May but shifted to underground dens in June shortly before parturition. The percentage of underground dens used each month was inversely related to the average monthly temperature (Fig. 2 A, B). The correlation was higher for 426 The American Midland Naturalist 100(2)

= = males (r -.84, ? < .01) than for females (r -.55, ? < .05) because females used underground dens during parturition and lactation (May and June) when the UNDERGROUNDDENS ABOVEGROUND SITES OTHER(HOLLOW LOGS, DEN TREES)

APRMAY JUN JUL AUGSEPT OCT NOV DEC JANFEB MAR APR MAY JUN JUL AUGSEPT OCT NOV 4(18)3(19) 3(11)'5(20) 6(10)6(15) 6(23) 8(90) 8(174)7(96)5(35) 5(54) 3(23)5(33) 6(34)5(35) 6(21) 6(23) 3(33) 3(21) 1968 1969

APRMAY JUNJUL AUGSEPT OCT NOV DECJAN FEBMAR APR MAY JUN JULAUG SEPT OCT NOV 5(47)5(77)4(37)3(5) 3(8) 2(10)5(16)8(104)8(189)7(103)6(52)6(61)4(18)2(18) 2(14)3(22)5(24) 4(16) 3(23)2(15) 1968 1969 Fig. 1.?Seasonal shifts in den types of striped skunks on the Cedar Greek Natural History Area, Anoka Co., Minnesota. (A) males, (B) females 1978 Houseknecht and Tester: Skunk Denning 427

average monthly temperature was relatively high. No strong correlation existed between the percentage of underground dens and the total monthly precipitation = = formales (r ?.33, ? > .05) or females (r .00, ? > .05). Although only 28 of 206 dens and only one of 183 aboveground rest sites were used by two or more skunks simultaneously or sequentially, 24 and 17 radio-marked skunks had indirect and direct contact, respectively, with other radio-marked skunks. Communal denning occurred seasonally only from the 3rd week in October through the 1st week of April. Storm (1972) reported a low incidence of communal denning during late summer and early autumn. No males were found denning concurrently during the present study, but as many as six females were found with one male. There was no significant difference in the frequency of communal denning for any = den type (x2 5.85, ? > .10). Two skunks had direct or indirect intraspecific contact with at least nine other skunks. Others were not observed using a den currently or previously occupied by another skunk. This variation might have been related, in part, to the distribution of radio-marked skunks on the study area. Trapping effort was concentrated near the radio towers; thus, the probability of trapping and locating an individual was inversely related to its distance from the receiving antennas. Both males and females tended to remain in one den for long periods during winter months. Females changed dens infrequently immediately after parturition and during lactation, but after the young began to travel with the females the family groups changed den locations every 1-2 days. Males changed den sites frequently from late winter through late autumn. The data were similar for all years and were pooled for analysis (Fig. 3 A, B). The average monthly distances between successive daily dens are given in Table 1. There was no significant difference between months for males or females (sign test, ? > .27). Males tended to move farther than females but the differences were not

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10 15 20 25 -15 -10 -5 0 5 AVERAGEMONTHLY TEMPERATURE (?C) Fig. 2.?Percentages of underground den-use of striped skunks in relation to average monthly temperature. (A) males, (B) females. Numbers in parentheses indicate sample sizes. Numbers outside parentheses indicate the number of individual skunks in the sample 428 The American Midland Naturalist 100(2)

? significant (t 0.86, ? > .10). Individual variation was great. Some skunks moved as much as 2.75 km between successive den sites.

Discussion Storm (1972) reported seasonal changes in the type of den used by striped skunks. During spring and summer skunks bedded aboveground but during autumn and winter they used underground dens, buildings and piles of brush and lumber (Storm, 1972: 43). Verts (1967) reported that juvenile skunks commonly denned aboveground in summer but none was known to have done so after mid-September. The high incidence of aboveground denning observed in this study would reduce possible indirect and direct contact because no aboveground rest site was used concurrently by more than one animal and only one site was used sequentially by more than one skunk. No previous worker has reported seasonal shifts in habitat type used for denning by skunks. In this study almost all lowland dens were aboveground, hence little direct or indirect contact would occur through concurrent or sequential use of dens. However, traveling to and from den sites in lowland areas could be important in contracting diseases such as leptospirosis which is transmitted by contact with infected urine under moist conditions (Salle, 1973: 919). Indirect contact through sequential use of dens is dependent upon several factors including species using the area, abundance of suitable den sites, patterns of den use and stability and permanence of dens. Kilgore (1969) found that many swift fox (Vulpes velox) dens in Oklahoma disappeared between spring and.autumn each year, but Shirer and Fitch (1970: 499) stated that "extensive and well-situated dens are the communal property of the population and are relatively permanent so that they are

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$ a JANFEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC JANFEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC 7(195)7(149)4(132)4(136)7(190)7(148)9(181)7(124)5(98) 8(147)6(175)8(220) 7(207)6(169) 7(121)6046) 5051) 5(74) 4(112) 4(101) 3(78) 6(121) 7(188) 7(217) Fig. 3.?Percentage of time that striped skunks changed successive den locations on Cedar Greek Natural History Area, Anoka County, Minnesota. (A) males, (B) females. Numbers in parentheses indicate the sample sizes. Numbers outside parentheses indicate the number of individual skunks in the sample

Table 1.?Average monthly distances (km) between successive den locations of striped skunks on the Cedar Creek Natural History Area, Anoka Co., Minnesota_ Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. X Males ? 1.34 .55 .52 .50 .61 .56 .40 .29 .35 .33 .81 .53 Animals(moves) 0(0) 1(1) 4(31) 5(59) 7(61) 6(34) 9(82) 6(46) 4(33) 6(67) 6(47) 2(5) Females .43 .24 .29 .50 .27 .50 .39 .35 .63 .26 .56 .43 Animals(moves) 1(1) 1(3) 3(11) 6(52) 3(8) 1(10) 4(44) 4(48) 2(24) 6(36) 7(51) 4(6) 1978 Houseknecht and Tester: Skunk Denning 429 least red fox (Vulpes vulpes), raccoons (Procyon lot or), three skunks and two opossums (Didelphis virginiana). Kilgore (1969) found many species (including striped skunks) in swift fox dens but did not indicate whether this represented sequential or concurrent use. Eight of 46 dens studied by Verts (1967) in 1960-1961 were used by two or more species. Mead (1963) reported that a species of flea (Pulex simulans) infected skunks occupying dens that had been used previously by feral cats (Felix catus). The low incidence of sequential den use in the present study is biased in that we have no information on the number of dens actually entered by skunks. Other studies have shown that skunks often enter as many as five (Allen and Shapton, 1942) or seven (Ferris and Andrews, 1966) dens during a single night. The frequency with which striped skunks change den locations is probably related to the number of suitable dens available. Verts (1967) found that a male skunk used one den continuously from 30 March to 23 April and alternated between this den and one other between 24 April and 2 May. Skunks on the University of Kansas Natural History Reservation (no? cropland) changed dens on 57.6% of the nights during December, February, March and early April (Shirer and Fitch, 1970). Storm (1972) reported that the mean number of dens for four different age and sex groups ranged from 8-12 within a 15-28 day period. Bailey (1971) reported that the number of dens available to animals on a Lake Erie marsh exceeded the demand and that skunks changed dens frequently. Shirer and Fitch (1970) reported a mean distance between successively used den sites that was comparable to the mean of this study (414 and 483 m, respectively). Their maximum record was 811 m, however, whereas in this study one skunk moved 2.75 km. Verts (1967) recorded one movement of 2.62 km between successive den sites. Results of this investigation indicated that, seasonally, there was a high degree of intraspecific direct and indirect contact through concurrent and sequential use of dens.

Acknowledgments.?The authors are indebted to Larry Kuechle and Ralph Schuster for construction of radio transmitters and maintenance of the automatic tracking system. Facilities of the Cedar Greek Natural History Area were made available through the cooperation of Dr. William Marshall and Alvar Peterson. Drs. Gerald Storm and B. J. Verts critically reviewed the manuscript. This research was supported by the United States Atomic Energy Commission (COO-1332-72) and by PHS Training Grant No. 5 TOI GM01779 from the National Institute of General Medical Sciences. Literature Cited Allen, D. L. 1939. Winter habits of Michigan skunks. /. Wildl. Manage., 3:212-228. -and W. W. Shapton. 1942. An ecological study of winter dens, with special reference to the eastern skunk. Ecology, 23:59-68. Bailey, T. N. 1971. Biology of striped skunks on a southwestern Lake Erie marsh. Am. Midi. Nat., 85:196-207. Bray, J. R., R. B. Lawrence and L. G. Pearson. 1959. Primary production in some Minne- sota terrestrial communities for 1957. Oikos, 10:38-49. Goghran, W. W. and R. D. Lord, Jr. 1963. A radio-tracking system for wild animals. /. Wildl. Manage., 27:9-24. Ferris, D. H. and R. D. Andrews. 1966. Parameters of a natural focus of Leptospira pomona in skunks and opossums. Bull. Wildl. Dis. Assoc, 3:2-10. Kartman, L., F. M. Prince and S. F. Quan. 1959. Epizootiologic aspects. In: The Oregon meadow mouse irruption of 1957-1958. Oregon State Coll. Fed. Coop. Ext. Serv. p. 43-54. Kilgore, D. L., Jr. 1969. An ecological study of the swift fox (Vulpes velox) in the Oklahoma Panhandle. Am. Midi. Nat., 81 -.512-534. Mead, R. A. 1963. Some aspects of parasitism in skunks of the Sacramento Valley of California. Ibid., 70:164-167. 430 The American Midland Naturalist 100(2)

Megh, L. D., V. B. KuEGHLE, D. W. Warner and J. R. Tester. 1965. A collar for attaching radio transmitters to rabbits, hares, and raccoons. /. Wildl. Manage., 29:898-902. Rongstad, O. J. and J. R. Tester. 1969. Movements and habitat use of white-tailed deer in Minnesota. Ibid., 33:366-379. Roth, E. E., W. V. Adams, G. E. Sanford, Jr., B. Greer, K. Newman, M. Moore, P. Mayeus and D. Linder. 1963. The bact?riologie and serologie incidence of leptospirosis among striped skunks in Louisiana. Zoonoses Res., 2:13-39. Salle, A. J. 1973. Fundamental principles of microbiology. McGraw-Hill, New York, ? + 1094 p. Selko, L. F. 1938. Notes on the den ecology of the striped skunk in Iowa. Am. Midi. Nat., 20:455-463. Seton, ?. T. 1926. Lives of game animals, vol. 2. Doubleday, Page and Co., Garden City, New York, xvii + 746 p. Shirer, H. W. and H. S. Fitch. 1970. Comparison from radio tracking of movements and denning habits of the raccoon, striped skunk, and opossum in northeastern Kansas. /. Mammal., 51:491-503. Soave, O. A. 1966. Transmission of rabies to mice by ingestion of infected tissue. Am. J. Vet. Res., 27:44-46. Storm, G. L. 1972. Daytime retreats and movements of skunks on farmlands in Illinois. /. Wildl. Manage., 36:31-45. Verts, B. J. 1967. The biology of the striped skunk. University of Illinois Press, Urbana. vii + 218 p.

Submitted 31 March 1977 Accepted 10 March 1978