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Seasonal Home Range and Diurnal Movements of Sylvilagus obscurus (Appalachian Cottontail) at Dolly Sods, West Virginia
Kelly A. Boyce and Ronald E. Barry

Northeastern Naturalist, Volume 14, Issue 1 (2007): 99–110

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2007 NORTHEASTERN NATURALIST 14(1):99–110 Seasonal Home Range and Diurnal Movements of Sylvilagus obscurus (Appalachian Cottontail) at Dolly Sods, West Virginia Kelly A. Boyce1,* and Ronald E. Barry1 Abstract - The purpose of the study was to estimate seasonal home ranges of Sylvilagus obscurus (Appalachian cottontail) within dense ericaceous and coniferous cover at its type locality, the Dolly Sods Scenic Area in West Virginia. Ninety-five percent adaptive kernel (AK) home ranges of rabbits ranged from 5.7–13.3 ha during the leaf-on season (May–September; n = 5) and 1.5–9.0 ha during the leaf-off season (October–April; n = 14). Fifty-percent AK core areas ranged from 0.9–2.5 ha during the leaf-on season and 0.1–2.5 ha during the leafoff season. Males occupied larger home ranges during the leaf-on than leaf-off season, but female ranges did not differ seasonally. These results demonstrate seasonal differences in spatial and associated resource requirements of Appalachian cottontails and the need for large tracts of appropriate habitat for travel lanes to maintain viable populations of this species. Introduction The historical range of Sylvilagus transitionalis (Bangs) (New England cottontail) extends from northern New England southward along the Appalachian Mountains to northern Georgia and Alabama (Fig. 1; Chapman 1975, Hall 1981). Because of their distinct cytotype (Ruedas et al. 1989) and different craniometrics, Chapman et al. (1992) accorded the southern populations of this taxon specific distinction as Sylvilagus obscurus (Chapman) (Appalachian cottontail). However, the status of S. obscurus as a specific entity is inconclusive based on mitochondrial DNA evidence (Litvaitis et al. 1997). Sylvilagus obscurus is confined to higher elevations in the Appalachian Mountains south and west of the Hudson River and ranges from northeastern Pennsylvania south. Its status in West Virginia is currently identified by the West Virginia Wildlife Diversity Program (2003) as a species “… somewhat vulnerable to extirpation,” and recently has been under consideration for listing on the IUCN Red List (Smith 2004). The Appalachian cottontail, similar to S. transitionalis to the north, has experienced a decline throughout its range over the last half century (Chapman et al. 1992). Populations presumably have been reduced by: 1) gradual climatic changes since the last glaciation; 2) habitat maturation, destruction, and fragmentation; and 3) the reinvasion of lowland areas by S. floridanus (J.A. Allen) (eastern cottontail) (Chapman and Morgan 1973; Chapman et al. 1977, 1992; Merritt 1987). 1Department of Biology, Frostburg State University, Frostburg, MD 21532. *Corresponding author - 100 Northeastern Naturalist Vol. 14, No. 1 Sylvilagus obscurus occupies high elevations in a mosaic of habitat refugia throughout its range (Chapman and Stauffer 1981, Chapman et al. 1982). In the central Appalachians, this species is typically found at elevations > 570 m in conifer stands, mixed-oak forest, or 6- to 9-year-old clearcuts, with extensive underlying ericaceous (heathlike) or Rubus allegheniensis (Porter) (blackberry) cover (Blymyer 1976, Boyce 2001, Chapman and Morgan 1973, Chapman and Paradiso 1972, Chapman and Stauffer 1981, Stevens and Barry 2002). Home-range size for S. transitionalis in Connecticut was reported as 0.2–0.7 ha (Dalke 1937). These estimates were made from live trapping in the fall months using comparatively few observations. Stevens and Barry (2002) reported comparatively large (1.4–9.0 ha) 95% adaptive kernel (AK) home ranges of radio-tracked S. obscurus in western Maryland. We initiated a study to examine the ecological parameters of S. obscurus in the type locality, the Dolly Sods Scenic Area of the Monongahela National Forest in West Virginia. This site of historical abundance (Chapman and Morgan 1973), characterized by extensive ericaceous (heathlike) and low-lying coniferous cover (Boyce 2001), has remained largely unchanged since the last systematic investigation in the 1970s (Chapman and Stauffer 1981, Venable 1996) due to high elevation and harsh climatic conditions that have arrested succession. The objectives of the study were to describe seasonal home ranges of S. obscurus at this site, determine any differences in home-range size between sexes, and compare sizes of ranges to those of western Maryland rabbits (Stevens and Barry 2002). Figure 1. Historical and present distribution of S. transitionalis/S. obscurus (after Chapman and Stauffer 1981). 2007 K.A. Boyce and R.E. Barry 101 We expected to find smaller home ranges than were reported for the Appalachian cottontail in western Maryland because of the greater density of cover and other resources at Dolly Sods (Boyce 2001, Sommer 1997, Stevens and Barry 2002). Further, we predicted both seasonal and sex differences in home-range size, with larger ranges expected during the breeding season and among males. The information gathered indicates the spatial resources necessary for the survival of individuals and perpetuation of local populations, and thus permits preliminary suggestions for strategies to effect management and conservation of the Appalachian cottontail in West Virginia and throughout its range. Methods Study area The study was conducted at the 970-ha Dolly Sods Scenic Area in Tucker County, WV (39º01'N, 79º19'W; Fig. 2). This windswept plateau of the Monongahela National Forest ranges in elevation from approximately 790 to > 1200 m. The biota of the area is characteristic of northern US and Canadian regions (Venable 1996). Conifers are abundant and include Picea rubens Sarg. (red spruce), Pinus resinosa Ait. (red pine), P. rigida Mill. (pitch pine), Tsuga canadensis L. (eastern hemlock), and Abies balsamea Mill. (balsam fir). Heaths (Ericaceae spp.) provide extensive cover, especially in the form of Kalmia latifolia L. (mountain laurel), Rhododendron maximum L. (rhododendron), and Vaccinium spp. (blueberries). High-mountain bogs are present. The weather is cool and wet, with > 140 cm annual precipitation, and yearly snowfall can reach 380 cm (Venable 1996). Procedure From October 1997 to April 1999, wooden box traps (18 x 22 x 60 cm; Sommer 1997) were used to live-trap rabbits in 19 areas throughout the study site. Rabbits were identified initially by a discriminant function model (Litvaitis et al. 1991) developed to distinguish S. transitionalis and S. Figure 2. Location of the Dolly Sods Scenic Area in West Virginia. 102 Northeastern Naturalist Vol. 14, No. 1 floridanus. Species identification was later confirmed by electrophoretic analysis of blood serum proteins (Chapman and Morgan 1973, Stevens and Barry 2002). After sex was determined, rabbits were ear-tagged and radiocollared so individuals could be tracked to their daytime locations. In our study, all rabbits were opportunistically tracked from dawn to dusk 0–5 times per week, depending on weather and/or travel constraints. Subjects usually were in view prior to flushing, but if not, a form or depression marked their exact locations. Night-time surveillance was logistically impractical due to extremely dense, low-lying ericaceous vegetation (Boyce 2001) that precluded us from confirming rabbits’ exact locations in the dark. Universal-Transverse-Mercator (UTM) grid coordinates were determined at radiolocations using a global positioning system (GPS) differentially corrected with PATHFINDER software (Trimble Navigation Ltd., Sunnyvale, CA) for improved accuracy (using GPS base-station data from the Soil Conservation Service office at Morgantown, WV). Successive locations for each individual were separated by > 24 h in an attempt to ensure independence of observations because White and Garrott (1990) suggested a sampling interval that allows an animal to move from one end of its home range to another. However, no consensus exists on the importance of autocorrelation in the estimation of home ranges. Hansteen et al. (1997) indicated that the degree of autocorrelation decreases normally with increasing time intervals between observations. However, Swihart and Slade (1997) suggested that autocorrelated data will not invalidate common estimators of home-range size as long as the study encompasses an adequate period of time. Otis and White (1999) agreed with this assessment, but suggested that the length of the sampling interval should be adequate so that autocorrelation does not affect home-range estimates and hypothesis tests involving them. DeSolla et al. (1999) concluded that accuracy and precision of home-range size estimates from simulated data improved with shorter time intervals despite the complication of autocorrelation. All rabbits were tracked until they died, transmitters failed, or radio signals were lost. Homerange estimates were generated by plotting locations for each individual using the program CALHOME (Kie et al. 1996) and were considered stabilized if a plot of home-range size against cumulative number of locations became asymptotic (Bowyer et al. 1995, Hansteen et al. 1997, Stickel 1954). Home ranges were estimated with the 95% adaptive kernel (AK) estimator (Worton 1989), which computes a probability density (kernel) over each location and then totals these kernels. In comparison to the minimum convex polygon, which is extremely sensitive to sample size and positively biased at small sample sizes (Seaman et al. 1999), the AK reduces the probability of including areas not occupied. Also, use of the AK estimator permitted comparisons with a study (Sommer 1997, Stevens and Barry 2002) in nearby Maryland. The AK bandwidth or smoothing parameters were reduced to the appropriate percentage of the selected optimum to obtain a balance between lowering least-squares cross-validation (LSCV) scores and minimizing 2007 K.A. Boyce and R.E. Barry 103 home-range fracture into many small, isolated areas (Kie et. al 1996, Sommer 1997). Seaman et al. (1999) recommended the use of LSCV methods to determine the amount of smoothing for kernel estimators. If efforts at smoothing to minimize fracture of the home range still produced additional, isolated regions, these multiple areas of activity were included in an individual’s home range. Home ranges were estimated for leaf-on (May– September) and leaf-off (October–April) seasons, the former corresponding roughly with the Appalachian cottontail breeding season (Chapman et al. 1977). A 50% AK estimate was used to describe areas of concentrated use, or the individual’s core area (Samuel et al. 1985). Comparisons of home-range size by sex and season, and with home ranges of S. obscurus in western Maryland, were evaluated with the Mann- Whitney test (Mann and Whitney 1947, Zar 1999). Statistical analyses were conducted with MINITAB 13 (Minitab, Inc., State College, PA). Based on their temporal segregation, 2 home ranges derived from a single individual in different seasons or years were considered independent for the purpose of statistical analysis; no individual generated > 2 home-range estimates. The criterion for statistical significance for all analyses was P < 0.05. Results Thirty-eight cottontails (37 S. obscurus, 1 S. floridanus) were captured at 17 of 19 sites sampled. Day home ranges of 14 individual (7 males, 7 females) S. obscurus reached asymptotes after a minimum of 18 locations (leaf-on season: 33–47 locations, mean ± 1 SD = 41 ± 6; leaf-off season: 18– 33 locations, mean ± 1 SD = 25 ± 5) and were included in the analysis. Five individuals (3 males, 2 females) provided 95% AK home-range estimates that ranged from 5.7–13.3 ha during the leaf-on season (Fig. 3). These ranges were larger (W = 76.5, P < 0.05) than the 14 home ranges (range = 1.5–9.0 ha) estimated from 13 individuals (6 males, 7 females, with 1 female generating estimates in both 1997–1998 and 1998–1999) during both leafoff seasons combined, and the 12 estimates (6 males, 6 females) from the 1998–1999 leaf-off season only (W = 70.5, P < 0.05). Home ranges of males in the leaf-on season were significantly larger (W = 24.0, P < 0.05) than those of males in the leaf-off season. Home ranges of females did not differ seasonally (W = 12.5, P > 0.05). Male home ranges did not differ from those of females in the leaf-on (W = 12.0, P > 0.05) or leaf-off (W = 43.0, P > 0.05) seasons. One male died from predation during the leaf-on season before his home range stabilized (not included in the analysis). His 95% AK home range was 30.7 ha after only 17 locations. On 2 occasions, this male was tracked to the locations of other radiocollared females whose radio signals were heard and which were seen. This male traveled a 0.84-km straight-line distance between successive locations in one 24-h period. Core areas (50% AK estimates) showed considerable individual variation with no discernible difference between sexes. During the leaf-on season, 4 of 5 rabbits concentrated their activity in 2 distinct regions of 104 Northeastern Naturalist Vol. 14, No. 1 the home range (Fig. 4), with recognizable areas of concentrated use (50% AK core areas) within each of these regions. During the leaf-off Figure 3. Ranges of sex-specific 95% adaptive kernel (AK) home ranges (ha) for the leaf-on (clear) and leaf-off (shaded) seasons at Dolly Sods Scenic Area in West Virginia, 1997–1999. Medians are indicated by lines within the bars. Sample size is to the right of the bar. Figure 4. CALHOME (Kie et al. 1996)-generated 95% and 50% adaptive kernel (AK) home ranges of a female Appalachian cottontail based on 33 locations in the leaf-on season at Dolly Sods Scenic Area in West Virginia. 2007 K.A. Boyce and R.E. Barry 105 season, 8 of 14 rabbits used a single major region of activity with 1–3 core areas. The other 6 rabbits used 2 distinct regions of the home range with 1 or 2 smaller core areas. Core areas (50% AK estimates) ranged from 0.9–2.5 ha in the leaf-on season (n = 5) and 0.1–2.5 ha in the leaf-off season (n = 14; Fig. 5). Core areas in the leaf-on season were significantly larger than those in the leaf-off season (W = 75.5, P < 0.05). The difference between the core areas of males in the leaf-on (n = 3) and leaf-off (n = 6) season was marginally nonsignificant (W = 23.0, 0.05 < P < 0.10); female areas (leaf -on: n = 2; leaf-off: n = 8) did not differ seasonally (W = 15.0, P > 0.05). Core areas did not differ between male and female rabbits in the leaf-on (W = 11.0, P > 0.05) or leafoff (W = 37.5, P > 0.05) seasons. Discussion Appalachian cottontails were distributed widely within the Dolly Sods Scenic Area and were captured at 17 of 19 trap sites. Appalachian cottontails occupied home ranges at elevations of 790–1200 m in patches of dense ericaceous vegetation and coniferous stands (Boyce 2001, Sucke 2002), consistent with what Chapman and Stauffer (1981) and Sommer (1997) Figure 5. Ranges of sex-specific 50% adaptive kernel (AK) home ranges (core areas– ha) for the leaf-on (clear) and leaf-off (shaded) seasons at Dolly Sods Scenic Area in West Virginia, 1997–1999. Medians are indicated by lines within the bars. Sample size is to the right of the bar. 106 Northeastern Naturalist Vol. 14, No. 1 found in western Maryland. This species appears to be locally widespread and abundant in this habitat (Boyce 2001, Sucke 2002), as it was in the 1970s (Chapman and Morgan 1973), indicating that Dolly Sods continues to support a viable population. The eastern cottontail apparently has not displaced the Appalachian cottontail at higher elevations at this location. Appalachian cottontails at Dolly Sods selected home ranges in macrohabitat characterized by dense, ericaceous vegetation, such as mountain laurel, rhododendron, and blueberries, and stands of conifers, especially red spruce. Rabbits used microhabitats with > 80% vegetative cover to a height of 1.5 m above the substrate (Boyce 2001). Ranges of S. obscurus in our study were considerably larger than those of 0.2–0.7 ha reported by Dalke (1937) for S. transitionalis in Connecticut, although the methodologies between the studies differed greatly. The hypothesis that the quality and quantity of habitat present at Dolly Sods might reduce the sizes of home ranges of Appalachian cottontails relative to those in western Maryland is not supported by our results. Home ranges of rabbits during the leaf-on season at Dolly Sods (n = 5; Fig. 3) were significantly larger (W = 83.0, P < 0.05) than those in the comparable season in western Maryland where similar data collection methods were used (range = 1.4–8.3 ha, median = 4.7 ha, n = 8; Stevens and Barry 2002), even though available resources appear to be more concentrated at the former location (Boyce 2001). Larger home ranges of Appalachian cottontails at Dolly Sods could be attributable to lower densities (Sucke 2002) when compared to those in other parts of the species’ distribution (Laseter 1999). However, in both Maryland and West Virginia studies, considerable individual and seasonal variation was observed, and larger sample sizes could provide further clarification. Seasonal differences in home-range size were expected and realized. Larger home ranges in the leaf-on season may have resulted from the comparative abundance of resources and cover, specifically, greater availability of food, reduced metabolic cost of exposure to ambient conditions, and reduced risk of predation (Brown and Litvaitis 1995, Litvaitis et al. 1985). Smaller ranges in the leaf-off season could be the result of limited resources during this physiologically stressful period. During the winter months, 3 radio-collared rabbits were found intact beneath the snow, having died presumably from exposure. It seems likely that harsh conditions in winter (i.e., low temperatures, heavy snowfall, high winds) restrict rabbit movement and thus home-range size; in winter rabbits spend more time in dense, evergreen vegetation that provides thermal cover (Boyce 2001). Home ranges were determined based on daytime locations only and may not reflect movements made throughout the night when rabbits are most active. However, Trent and Rongstad (1974) found little difference between day- and nighttime home ranges of S. floridanus, although they monitored only 4 rabbits over a 9-day period. We expected that male Appalachian cottontails would have had larger home ranges than females during the leaf-on or breeding season. However, 2007 K.A. Boyce and R.E. Barry 107 we found no difference between sexes in home-range size, largely because of the low power (small sample size) of our statistical test and our exclusion from analysis of the male with the largest home range because of insufficient number of data points. Home ranges of male eastern cottontails were reported by Althoff and Storm (1989) to be larger than those of females for all seasons except winter, with differences most notable in the summer. Trent and Rongstad (1974) found that the smaller home-range size of females was likely attributed to restricted movements near the nest and greater availability of food and cover during spring and summer, although cover also could influence male home-range size. Althoff and Storm (1989) found that some males had home ranges that were considerably larger than other males because these males bred with more than one female. This finding is consistent with the idea that dominant males have larger home ranges as a result of a dominance hierarchy (Trent and Rongstad 1974) and with our observation that the male whose range was 30.7 ha and still had not stabilized was spatially associated with 2 radiocollared females during the breeding season. Leaf-on core areas were larger than leaf-off core areas presumably because core area is relative to the size of seasonal home range. The correspondence of sizes of core areas with sizes of home ranges of individuals is consistent with the individual differences we observed among rabbits in their use of space. Based on the sizes of home ranges in our study, and the spatial and other resource requirements (i.e., food, cover) of Appalachian cottontails reflected by such ranges, it is evident that expansive, unfragmented (or at least connected) areas of appropriate habitat are necessary for the maintenance of viable populations of Appalachian cottontails. New England cottontails occupying large patches (> 5.0 ha) had higher survival rates than individuals occupying small patches (< 2.5 ha) because of quality of habitat and forage (Barbour and Litvaitis 1993, Villafuerte et al. 1997). Fragmentation of habitat and prevention of natural fires and succession (Chapman and Morgan 1973) may reduce the suitability of areas for this species in West Virginia. Fragmentation and loss of habitat are cited as leading causes of species extinctions (Soule 1991). On a landscape scale, New England cottontails had lower survival rates in fragmented landscapes than in more even landscapes (Brown and Litvaitis 1995). If large patches are not maintained and properly managed, the Appalachian cottontail will become vulnerable to local extinctions. Efforts to conserve expansive areas of appropriate habitat are essential for the conservation of this species. Acknowledgments We thank the West Virginia Division of Natural Resources and Frostburg State University for the funding of this project and the US Forest Service for permission to use the Dolly Sods area for the study and for use of one of their nearby cabins. Alana Sucke, Nancy Bensley, Jeff Peters, and Michael Boyce contributed much time and 108 Northeastern Naturalist Vol. 14, No. 1 effort in the field. Mitch Spear loaned his snowmobile to the project. Drs. J. 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