American black bear estrus and parturition in the Alleghany Mountains of Virginia

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1 American black bear estrus and parturition in the Alleghany Mountains of Virginia Author(s) :Andrew S. Bridges, Michael R. Vaughan, and Josephine A. Fox Source: Ursus, 22(1): Published By: International Association for Bear Research and Management DOI: URL: BioOne ( is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne s Terms of Use, available at Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. PersonIdentityServiceImpl

2 American black bear estrus and parturition in the Alleghany Mountains of Virginia Andrew S. Bridges 1,4, Michael R. Vaughan 2, and Josephine A. Fox 3 1 Institute for Wildlife Studies, 2515 Camino Del Rio South, San Diego, CA 92108, USA 2 Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA , USA 3 Saint Louis University, St. Louis, MO 63103, USA Abstract: Timing of parturition and, to a lesser extent, estrus, are rarely explored aspects of American black bear (Ursus americanus) reproductive ecology. The Cooperative Alleghany Bear Study was an intensive 10-year multi-faceted research project conducted on 2 study areas in western Virginia. We examined timing of estrus based on 430 observations of 326 lone (without cubs at the time of capture) female bears from late May August, We estimated parturition date for 383 cubs from 150 litters born from to 99 individual females ranging from 3 24 years old. Bears were documented in estrus from late May through August with a peak during early July. Parturition dates ranged from late December to mid February with most births occurring in mid January. Three- and 4-year olds gave birth, on average, 12 days later than older bears. We suggest parturition date likely affects den exit date and perhaps cub survival, an area requiring further inquiry. Key words: American black bear, birth, breeding, cub, estrus, parturition, reproduction, Ursus americanus, Virginia Reproductive research is relatively simple for species that reproduce frequently and produce easily observed offspring. However, American black bears (Ursus americanus) have relatively slow reproductive rates (Bunnell and Tait 1981) and must be studied for multiple years (LeCount 1982), or even decades (Pelton and van Manen 1996), in order to draw valid inference. Further complicating research efforts, black bears give birth in secluded dens that prevent long-distance observation and, if entered, involve considerable risk to both researcher and study animal (Godfrey et al. 2000). Thus, obtaining sample sizes that allow for elucidation of fine-scale patterns and examination of influential factors can prove challenging. Documentation of breeding season through observations of females in estrus is common in ursid research; however, it is rarely geographically and temporally contextualized. Parturition date and associated influences rarely have been quantified in bears (Bridges et al. 2002) and could play a role in aspects of bear population ecology such as cub survival. Our objectives were to document timing of, 4 bridges@iws.org and possible influences on, estrus and of parturition of American black bears. Study areas Our research was conducted on 2 study areas (Fig. 1) in the Alleghany Mountains of western Virginia, USA. Approximately 160 km apart, both study areas were on the George Washington Jefferson National Forests. The 840 km 2 northern study area in Augusta and Rockingham counties was centered near Reddish Knob at 38u289N, 79u159W. The 1,544-km 2 southern study area in Craig, Giles, and Montgomery counties was centered near Mountain Lake at 37u229N, 80u319W. Elevations of these 2 study areas ranged from 480 1,360 m (Kozak 1970), and common tree species included: eastern hemlock (Tsuga canadensis), sugar maple (Acer saccharum), beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), chestnut oak (Quercus prinus), pitch pine (Pinus rigida), white oak (Q. alba), black oak (Q. velutina), northern red oak (Q. rubra), yellow poplar (Liriodendron tulipifera), eastern white pine (P. strobus), mountain laurel (Kalmia latifolia), and 1

3 2 BLACK BEAR ESTRUS AND PARTURITION N Bridges et al. Fig. 1. Study areas of the Cooperative Alleghany Bear Study in western Virginia, USA. We conducted research on the northwestern study area from and on the southwestern study area from scrub oak (Q. ilicifolia; Rawinski et al. 1994). Temperatures ranged from an average high of 24uC in July to an average low of 29uC in January with total precipitation averaging 125 cm, including 134 cm of snow (Southeastern Regional Climate Center 2010). Methods General We captured bears with Aldrich spring-loaded foot snares and culvert traps (Johnson and Pelton 1980) from late May August We initiated trapping on our northern study area in 1994 and on our southern study area in We sedated captured bears with a mixture of ketamine hydrochloride and xylazine hydrochloride (200:100 mg/ml; 1 ml/45.5 kg; White et al. 1996) administered via dart pistol, blowpipe, or jab stick. Yohimbine hydrochloride (5 mg/ml; 2 ml/45.5 kg) was used as an antagonist for the xylazine hydrochloride. After bears were sedated, we determined their sex, weighed them, recorded morphometric measurements, and examined females for signs of estrus or lactation. To determine age, we removed a premolar (Willey 1974), which was sent to Matson s Laboratory (Milltown, Montana, USA) for cementum annuli analysis. We attached individually-numbered, plastic, perma-flex, stud-style eartags (National Band and Tag, Newport, Kentucky, USA) to all bears.6 months old and we tattooed all bears upper lips. We administered a tetracycline antibiotic to prevent infection and serve as a permanent biomarker in teeth and bones (Johnson 1964, Garshelis and Visser 1997). To track bears, we used radiocollars (Advanced Telemetry Systems [ATS], Isanti, Minnesota, USA; Lotek, Newmarket, Ontario, Canada; Telonics, Mesa, Arizona, USA; Wildlife Materials International, Murphysboro, Illinois, USA) that were equipped with breakaway cotton spacers (Hellgren et al. 1988), or eartag transmitters (Servheen et al. 1981) from ATS. We located dens in late fall and winter. We entered (Godfrey et al. 2000) these dens from January April, , to gather reproductive data, take morphometric measurements, change transmitters on adults, attach transmitters to cubs (Echols 2000, Vashon et al. 2003) and yearlings, and deploy remote cameras (Bridges et al. 2004). The Virginia Polytechnic Institute and State University Animal Care and Use Committee approved ( F&W) all animal-handling protocols. Hard-mast surveys (Sharp 1958, Coggin and Peery 1973), which involved annual examination of selected trees and quantification of the mean number of

4 BLACK BEAR ESTRUS AND PARTURITION N Bridges et al. 3 acorns/10 limbs/tree (Fearer et al. 2002), were conducted annually by the Virginia Department of Game and Inland Fisheries (VDGIF). We used these data (D. Martin, VDGIF, Verona, Virginia, USA, unpublished data) for the 3 survey regions overlapping our study areas to index annual autumn hardmast availability. Estrus All.2-year-old female bears trapped during summers were examined for indicators of estrus. These indicators included vulval swelling, vascularization (based on coloration), and discharge. Breeding season estimation was based on the relative proportion of.2-year-old, lone (not with cubs) female bears that exhibited indicators suggesting estrus during a given time interval. Because annual trapping did not commence and cease on the same dates every year and sample sizes for females were small during some periods, we could not examine annual variation nor could we use a daily time step to examine estrus timing. Thus, we pooled years and subdivided the summer trapping season into 10, 10- day intervals beginning 22 May and ending 31 August. We tested for differences in distribution of estrus timing on the 2 study areas and between age classes (3 4-year olds vs..5-year olds) using a nonparametric Kolmogorov-Smirnov (KS) test. Parturition date We estimated parturition date for each cub using a morphometry-based mixed regression model developed from known-age captive-born black bear cubs (Bridges et al. 2002). For multi-cub litters, we used mean values. We hypothesized that variation might result from maternal age, litter size, or nutritional stress due to hard-mast failure. We subdivided our sample into 2 age classes (3 4-year olds versus.5- year olds), 2 litter size groups (1 2-cub litters versus 3 4-cub litters) and 2 year groups (1998, following a hard-mast failure versus all other years). We then tested for effects and interactions using factorial ANOVA and compared least square means (LS x ) and associated variance. RESULTS Estrus Timing of estrus was based on 430 observations of 326 bears from late May August, Females began coming into estrus in late May. We observed a Fig. 2. Proportion of females in estrus with associated 95% confidence intervals based on yearold lone (not nursing cubs) individual female black bears observed 430 times, May August, in the Alleghany Mountains of western Virginia, USA. peak in estrus during early July followed by a gradual decline through August (Fig. 2). Patterns were not statistically different (D , P ) between study areas or between age classes. Parturition date We estimated parturition date for 383 cubs from 150 litters born from to 99 individual females ranging from 3 24 years old. We observed 1 anomalous birth date from a 24-year-old female whose single cub we estimated to have been born on February 18. Because both the age class of the female (5 years older than any other female) and the associated litter s birth date (14 days later than any other litter) were severe outliers in our data set, we excluded this data point from cumulative calculations. For the remaining 149 litters, estimated parturition date ranged from 26 December to 4 February with a mean and median of 17 January and a mode of 22 January. Litters were born from late December (2.7%) into February (6.0%), with most births occurring in January (91.3%). Distribution of birth dates was roughly bimodal with peaks in earlymid and mid-late January (Fig. 3). Maternal age class (3 4-year olds versus.5-year olds) strongly affected parturition date (F ; 1, 141 df; P,0.001; Table 1; Fig. 4). Analyses examining effects of a mast failure in 1997, which may have affected cubs born in the winter of 1998, revealed that when compared with all other nonmast failure years, there was little evidence (F ; 1, 141 df; P ) to support an effect on

5 4 BLACK BEAR ESTRUS AND PARTURITION N Bridges et al. Fig. 3. Distribution of estimated parturition dates and associated 95% confidence intervals from 149 litters of black bear cubs born from in the Alleghany Mountains of western Virginia, USA. birth date. Likewise, no effect of litter size (1 2 cubs versus 3 4 cubs) or 2- or 3-way interactions among factors were revealed (F ; 1, 141 df; P ; Table 1). Further examination of the effect of age class revealed that 3 4-year-old females had later parturition dates (LS x 5 28 Jan, SE 5 3 days, 95% CI 5 22 Jan 2 Feb) than.5-year olds (LS x 5 16 Jan, SE 5 1 day, 95% CI Jan). An interaction between mast failure and age class was not strongly supported (F ; 1, 141 df; P ; Table 1). Although LS x point-estimates were slightly later for 3 4-year olds following the mast failure (LS x 5 1 Feb, SE 5 4 days, 95% CI 5 24 Jan 8 Feb) than for non-failure years (LS x 5 24 Jan, SE 5 4 days, 95% CI 5 15 Jan 1 Feb), small sample size for 1998 (n 5 6) left us with little statistical power to detect a difference if it occurred. Confidence intervals for.5-year olds following the mast failure (LS x 5 15 Jan, SE 5 2 days, 95% CI Jan) substantially overlapped with confidence Table 1. Results from analysis of variance with factorial treatment arrangement examining differences in parturition date from 149 litters of American black bear cubs born from in the Alleghany Mountains of western Virginia, USA. Source df Mean square error F P Age class a 1 1, ,0.001 Mast failure b Litter size class c Age class x mast failure Age class x litter size class Mast failure x litter size class Age class x mast failure x litter size class Error a 3 4-year olds versus.5 year olds. b 1998 (following mast failure in autumn of 1997) versus all other years pooled. c 1 2-cub litters versus 3 4-cub litters.

6 BLACK BEAR ESTRUS AND PARTURITION N Bridges et al. 5 Fig. 4. Age-specific proportions and 95% confidence intervals of parturition dates from 23 litters of black bear cubs born to 3 4-year-old mothers and 126 litters born to.5-year-old mothers born from in the Alleghany Mountains of Virginia, USA. intervals following non-failure years (LS x 5 Jan 16, SE 5 1 day, 95% CI Jan). Discussion and management implications Estrus Timing of estrus did not differ between our 2 study areas. The pattern we documented (Fig. 2) was consistent with results of previous studies from Pennsylvania (Alt 1989), northern Mexico (Doan- Crider and Hellgren 1996), Tennessee (Eiler et al. 1989), Idaho (Reynolds and Beecham 1980), Washington (Lindzey and Melsow 1977), Minnesota (Rogers 1987), Ontario (Kolenosky 1990), and Alaska (Schwartz and Franzmann 1991). Cumulatively, these findings suggest that breeding season peaks in the early summer throughout the American black bear s nearly continental range. Photoperiod is related to breeding season timing for most mammals (Sadleir 1973), and the generally solstitial American black bear breeding season suggests a similar relationship. Because birth date can influence juvenile survival, mammalian breeding seasons are typically timed so that young are born at an optimum time to maximize their survival probability (Lack 1954). However, for species such as bears that delay implantation of blastocysts (Hamlett 1935), breeding season is essentially independent of parturition date and thus subject to a different suite of selection pressures. Spady et al. (2007) proposed that the breeding seasons for bear species evolved in response to seasonal food limitations during the Pliocene and Pleistocene glaciations and still persists today. Rogers (1987) suggested that black bear breeding season occurs in the summer due to the proximal constraint of spring den emergence and distal constraint of autumnal hyperphagia. Sandell (1990:31) proposed that mate-competition theory, competition among males in optimal condition when high-quality resources are easily available, might play a role in breeding season timing for species that delay implantation. Physical competition among male bears affects mating access and success (Kovach and Powell 2003) and, although often considered a period of low

7 6 BLACK BEAR ESTRUS AND PARTURITION N Bridges et al. nutrient availability (Beeman and Pelton 1980, Eagle and Pelton 1983), early summer access to neonatal ungulate prey (Schlegel 1976, Mathews and Porter 1988, Schwartz and Franzmann 1991, Kunkel and Mech 1994, Miller 1994, Ballard et al. 1999, Bull et al. 2001) may provide a high-protein high-quality resource and facilitate mate competition. These theories are not mutually exclusive, and a combination of factors may play a role. Parturition date Though parturition dates are readily available for captive black bears (Spady et al. 2007), quantitative estimates of parturition dates for wild black bears are rare in published literature (Bridges et al. 2002). This is likely because of the time investment required to estimate black bear parturition date based on auditory observation outside den sites. We found a January peak in births similar to that described by Alt (1983); however, we also found a roughly bimodal parturition date distribution (Fig. 4) with younger females (3 4-year olds) giving birth an average of 12 days (LS x ) later than older (.5-year olds) females. The 24-year-old outlier in our study gave birth approximately 2 weeks later than any other female (ages 3 19). Elderly bears are rare in most studies (Schwartz et al. 2003) and, although results from a single datum should be considered anecdotal, this could suggest implantation timing might be affected as females approach reproductive senescence. Quantification of factors influencing implantation and birth date is an underexplored aspect of black bear reproductive biology (Bridges et al. 2002, Spady et al. 2007). The later birth dates documented for younger females suggest implantation timing may differ among age classes. It is possible that later implantation and parturition provides caloric and metabolic advantages to younger, smaller females by delaying correspondingly den emergence (Bridges et al. 2004) until later in the spring when more food resources generally are available to support energy expenditures associated with foraging and concurrent lactation. However, manipulative experiments, likely involving captive bears, ultrasound, and tracking hormonal profiles while controlling for age, nutritional, and environmental (e.g., temperature and light) variables, will likely be necessary to more fully examine causal influences on implantation timing and parturition date. Field biologists gathering reproductive data at den sites may wish to consider how maternal age may affect birth dates of cubs and use this information in planning appropriate times for den visitations. Additionally, parturition timing has been demonstrated to affect offspring survival in large mammals (Smith and Anderson 1998, Testa et al. 2000), and a relationship between parturition timing and den emergence has been documented in American black bears (Bridges et al. 2004). However, how timing of parturition and den emergence affects bear cub survival remains relatively unexplored. Acknowledgments Primary funding for this research was provided by the Virginia Department of Game and Inland Fisheries (VDGIF) through the Federal Aid in Wildlife Restoration Project WE-99-R, Virginia Polytechnic Institute and State University, the Virginia Cooperative Fish and Wildlife Research Unit, and the US Forest Service. Additional support was provided by Georgia Pacific, National Fish and Wildlife Foundation, National Geographic Society, Northern Shenandoah Audubon Society, Safari Club International, Union Camp Corporation, Virginia Bear Hunters Association, Virginia Department of Transportation, Virginia Houndsmen and Sporting Dog Association, Virginia Chapter of the Sierra Club, Virginia Wilderness Committee, Wildlife Forever Foundation, and Westvaco. We thank VDGIF field biologists: J. Blank, A. Bourgeois, O. Burkholder, L. Crane, F. Frenzel, M. Gautier, R. Houck, J. Huffer, D. Kocka, D. Martin, B. Mohler, J. Pound, R. Propst, R. Schwartz, K. Sexton, G. Sours, B. Stinson, J. Watson, and W. Zollman, and Virginia Tech graduate students: C. Godfrey, R. Gray, J. Higgins, K. Higgins, S. Klenzendorf, D. Lee, C. Olfenbuttel, K. Needham- Echols, D. O Neil, and C. Ryan. Additionally, we thank the dozens of technicians and volunteers who assisted with fieldwork and data entry. Finally, we thank J. Fraser, D. Stauffer, D. Steffen, and J. Walters for their comments and suggestions. Literature cited ALT, G.L Timing of parturition of black bears (Ursus americanus) in northeastern Pennsylvania. Journal of Mammalogy 64: Reproductive biology of female black bears and early growth and development of cubs in northeaster Pennsylvania. Dissertation, West Virginia University, Morgantown, West Virginia, USA.

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