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Rest-site Activity Patterns of Eastern Spotted Skunks in Alabama
Isik W. Benson, Tyler L. Sprayberry, William C. Cornelison, and Andrew J. Edelman

Southeastern Naturalist, Volume 18, Issue 1 (2019): 165–172

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Southeastern Naturalist 165 I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 22001199 SOUTHEASTERN NATURALIST 1V8o(1l.) :1186,5 N–1o7. 21 Rest-site Activity Patterns of Eastern Spotted Skunks in Alabama Isik W. Benson1,*, Tyler L. Sprayberry1,2, William C. Cornelison1, and Andrew J. Edelman1 Abstract - Spilogale putorius (Eastern Spotted Skunk) is a nocturnal small carnivore that uses sites within cover for resting, raising of young, and protection from predators and inclement weather. We examined activity patterns of male radio-collared Eastern Spotted Skunks in Alabama by placing game cameras at resting-site entrances during winter and spring. Monitored skunks were strictly nocturnal and were never active before sunset or after sunrise. Ambient temperature and moon illumination influenced skunk activity, with greater aboveground activity occurring at greater ambient temperatures and lower moon illumination. Lower ambient temperatures may decrease skunk activity due to greater thermoregulatory costs and less prey availability. Skunks may reduce aboveground activity during times of greater moon illumination due to increased vulnerability to predation. Introduction Spilogale putorius (L.) (Eastern Spotted Skunk) occurs throughout the southeastern and midwestern United States (Kinlaw 1995). Eastern Spotted Skunks occupy areas of dense vegetation or rocky cover in grasslands, forests, and shrublands (Kinlaw 1995; Lesmeister et al. 2008, 2009, 2013; Sprayberry and Edelman 2018; Thorne et al. 2017). They primarily feed on insects and small mammals, but also eat reptiles, amphibians, plant material, fungi, birds, and bird eggs (Crabb 1941, Howell 1906, Selko 1937, Sprayberry and Edelman 2016). Little is known regarding the activity patterns of Eastern Spotted Skunks, but they are reported to be strictly nocturnal and less active as moon illumination increases (Manaro 1961, McCullough and Fritzell 1984). Rest sites are used for resting and protection from inclement weather and predators (Crabb 1948). Eastern Spotted Skunks typically locate rest sites within and among existing protective cover including shrubs, debris piles, burrows, hollow logs/stumps, tree cavities, rocks, and buildings (Crabb 1948, Kinlaw et al. 1995, Lesmeister et al. 2008, Sprayberry and Edelman 2018). Eastern Spotted Skunks were once prevalent throughout the eastern United States, but their population has been in decline since the 1940s, although the cause is unknown (Gompper and Hackett 2005, Nilz and Finck 2008). The IUCN Red List recently reclassified the Eastern Spotted Skunk as vulnerable (Gompper and Jachowski 2016), and many states consider it a species of conservation concern (Gompper and Hackett 2005, Sprayberry and Edelman 2018). Conservation of this elusive mammal is hampered by the lack of knowledge regarding its Department of Biology, University of West Georgia, Carrollton, GA 30118. 2Office of Environmental Services, Georgia Department of Transportation, Atlanta, GA 30308. *Corresponding author - isikwbenson@gmail.com. Manuscript Editor: Roger Perry Southeastern Naturalist I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 2019 Vol. 18, No.1 166 natural history and population status (Gompper and Jachowski 2016). Herein, we report rest-site activity patterns of male Eastern Spotted Skunks in the southern Appalachian Mountains of Alabama. This study of skunk activity provides insight into foraging behavior and vulnerability to predation, as well as how to improve monitoring methodology. Field-Site Description The study area was located in Alabama’s Talladega National Forest (171,643 ha), which stretches across Calhoun, Cherokee, Clay, Cleburne, and Talladega counties. Within the Talladega National Forest, we monitored Eastern Spotted Skunks primarily in and adjacent to Cheaha Wilderness Area (2944 ha), Dugger Wilderness Area (3723 ha), and Cheaha State Park (1133 ha). The Talladega National Forest lies at the confluence of the Piedmont and Ridge and Valley regions in northeastern Alabama and includes the southernmost reaches of the Appalachian Mountains. The terrain is rugged (elevation varies from 152 m to 735 m), with ridgetops dominated by Pinus spp. (Pine) and steep riparian valleys covered primarily in hardwoods (Quercus spp. [oak], Carya spp. [hickory], Liriodendron tulipifera L. [Tulip Tree], and Acer rubrum L. [Red Maple]) (Sprayberry and Edelman 2018). The wilderness areas and Cheaha State Park contain the 2 highest points in Alabama and have steeper slopes on average than the rest of the surrounding lands. The Talladega National Forest has active prescribed-fire and timber programs, but the wilderness areas and Cheaha State Park are not managed with fire or logging (USDA Forest Service 2004). However, natural disturbances (wildfire, wind and ice storms, and insect outbreaks) still influence forest structure in these areas (USDA Forest Service 2004). The region has a humid subtropical climate. Average annual precipitation in the Talladega National Forest is 141 cm, with an average annual high temperature of 23 °C and an average annual low temperature of 9 °C (https:// mesowest.utah.edu/). Methods Eastern Spotted Skunks were radio-collared (Model LPM-2800, Wildlife Materials, Murphysboro, IL) during 2015–2016 as part of a larger project on habitat use (Sprayberry and Edelman 2016, 2018). All trapping and handling methods were in accordance with the guidelines of the American Society of Mammalogists (Sikes et al. 2016), the University of West Georgia Institutional Animal Care and Use Committee (Protocol #1003), and the Alabama Department of Conservation and Natural Resources (Permit #2015044275468680). We tracked skunks at least once per week to their daytime rest sites by homing via radio telemetry (White and Garrott 1990). At a subset of sites, we opportunistically placed infrared-flash game cameras (Model 990i, Moultrie, Birmingham, AL) to record behavior and activity of skunks. We secured each camera to a nearby tree and aimed at a rest-site entrance. Cameras were set to take a 3-photo burst when triggered, with 5 seconds between triggered events. The footer of each picture recorded time, date, and ambient temperature (Fig. 1). Southeastern Naturalist 167 I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 2019 Vol. 18, No. 1 A skunk was considered to be active aboveground when it was observed to fully exit the rest site (emergence) and inactive when it fully entered the site (entrance). The analysis only used complete activity records that included both the first emergence and the last entrance from a site during a night by a radio-collared skunk. Because multiple adult Eastern Spotted Skunks are not known to share rest sites at the same time on our study area (Sprayberry and Edelman 2018), we assumed the radio-collared skunk that appeared in subsequent photographs during a night was the same individual. We calculated the first emergence time relative to sunset and the last entrance time relative to sunrise during a night for each activity record at a site. We calculated the total number of paired emergence/entrance observations during a night for each activity record and determined the total time a skunk was active each night as the time between the first emergence record and the last entrance record. We then figured the total time active aboveground each night by subtracting periods spent underground by a skunk from the total time active. To account for variation in night length across the year, the proportion of the night active by skunks was examined as both the total time active divided by night length and the total time active aboveground divided by night length. To examine variation in skunk activity, we divided the night into 4 periods: evening (sunset–20:59), early night (21:00–23:59), late night (0:00–2:59), and early morning (3:00–sunrise). Then, for each night period, we calculated the proportion of activity records that included any length of aboveground activity. All means reported are ± SE. We used multiple linear regression to examine the relationship between the total time active aboveground and environmental variables including night length, rainfall (absence/presence), ambient temperature at first emergence from rest site, and relative proportion of moon illuminated (low/high). Given the small range of values, we coded moon illumination as low (less than 0.5) or high (≥0.5). Total precipitation during a night was obtained from the Mesowest Surface Weather database using Figure 1. A male Eastern Spotted Skunk returning to a rest site during early morning hours. Southeastern Naturalist I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 2019 Vol. 18, No.1 168 the nearest weather station (http://mesowest.utah.edu/). Ambient temperature for each activity record was recorded from the photograph footer. Sunset and sunrise times and moon illumination data were obtained from the US Navy’s Astronomical Applications (http://aa.usno.navy.mil/index.php). Results We recorded 38 complete activity records (i.e., observed first emergence and final entrance from a site each night) on 4 individual male skunks at 6 rest sites from February to May 2015 and during March 2016. Females were not included in this study because of low capture success (Sprayberry and Edelman 2018). The rest sites monitored were burrows: 4 in the ground, 1 in a stump, and 1 at the base of an uprooted tree. Average number of complete activity records per individual was 9.3 ± 6.3 events, but 1 individual accounted for 76% of activity records. Skunks were completely nocturnal and emerged from rest sites at an average of 165.4 ± 28.8 minutes past sunset (min–max = 12–589 minutes, n = 38) and re-entered rest sites for the final time an average of 132.1 ± 21.6 minutes before sunrise (min–max = 30–552 minutes, n = 38). The average number of paired restsite emergence and entrance observations for a skunk each night was 1.6 ± 0.1 (min–max = 1–3 observations, n = 38). The total time active each night (i.e., first emergence to last entrance) averaged 419.3 ± 31.8 minutes (min–max = 88–658 minutes, n = 38). The average total time active aboveground each night was 325 ± 28.4 minutes (min–max = 88–580 minutes, n = 38). On average, skunks were proportionally active 60 ± 5 percent of the night (min–max = 11–92%, n = 38), but when adjusted by subtracting out periods of time spent below ground the average dropped to 47 ± 5 percent (min–max = 11–92%, n = 38). The proportion of activity records that included any length of aboveground activity (n = 38) did not dramatically differ between evening (76%), early night (71%), late night (79%), or early morning periods (84%). A multiple regression model (F2,35 = 46.0, P < 0.0001, adjusted R2 = 0.69) was fitted to examine how the total active time aboveground by skunks varied with ambient temperature (P < 0.001) and moon illumination (P < 0.01). Presence of rainfall and night length were not significant predictors of activity (P > 0.05) and were not included in the final model. For each 1 °C increase in ambient temperature, the time skunks were active aboveground increased by 20.2 ± 2.3 min (Fig. 2). At low levels of moon illumination, the time active aboveground increased by 116.5 ± 38.2 min compared to activity during high levels of moon illumination. Discussion Our results provide a picture of nightly male Eastern Spotted Skunk activity at rest sites in the southern Appalachian Mountains during winter and spring. Skunks on our study site were strictly nocturnal and only active aboveground about half of the night during these seasons. They typically emerged from sites 2–3 hours after sunset and reentered 2 hours before sunrise. During the active period, they often reentered and exited the site at least once before final reentra nce. Southeastern Naturalist 169 I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 2019 Vol. 18, No. 1 Environmental conditions impacted overall skunk activity levels during winter and spring. Presence of rainfall and night length had no observable effect, but ambient temperature and, to a lesser extent, moon illumination did impact skunk activity. Aboveground activity was impacted strongly by ambient temperature, with skunks being active longer when nights were warmer. Spending less time aboveground at low ambient temperatures likely reduces thermoregulatory costs for Eastern Spotted Skunks, which may be significant given their small body size (Kinlaw 1995). Prey availability may also decrease at lower ambient temperatures particularly for small mammals, arthropods, and herpetofauna (Crabb 1941). However, this study was conducted in late winter and spring in the southern portion of the Eastern Spotted Skunks range. Changing temperature may have a different observable effect for populations that are further north and during different seasons. High levels of moon illumination also negatively influenced skunk activity. Skunks were more active on nights with low levels of moon illumination, confirming previous anecdotal reports (Manaro 1961). Eastern Spotted Skunks have relatively low annual survival rates (35%), with mammalian and avian predation as the primary source of mortality (Lesmeister et al. 2010). High levels of moon illumination can increase hunting success of predators that rely on vision (Prugh and Golden 2014). By limiting activity on brighter nights, Eastern Spotted Skunks may decrease their vulnerability to predation. Our findings support that Eastern Spotted Skunks are primarily nocturnal as found in a previous study in Missouri that monitored 1 male skunk during spring, summer, and fall (McCullough and Fritzell 1984). Spilogale gracilis Merriam Figure 2. Total time active aboveground for Eastern Spotted Skunks observed at rest sites increased with increased ambient temperature in Alabama during February–May. Circles represent observations of skunk activity (n = 38). Fitted trend line is from a multiple regression model with total time aboveground as the response variable and ambient temperature as the explanatory variable during low levels of moon illumination. Southeastern Naturalist I.W. Benson, T.L. Sprayberry, W.C. Cornelison, and A.J. Edelman 2019 Vol. 18, No.1 170 (Western Spotted Skunk) is also mostly active at night (Crooks and Van Vuren 1995, Neiswenter et al. 2010). By strictly limiting activity to nighttime, spotted skunks likely lower their vulnerability to diurnal predators. Although larger skunk species like Mephitis mephitis (Schreber) (Striped Skunk) and Conepatus humboldtii Gray (Humboldt’s Hog-nosed Skunk) also tend to be nocturnal, their activity is not limited as strictly by sunset and sunrise (Johnson et al. 1988, Larivière and Messier 1996). This could be due to lower overall mortality from predation in these larger skunk species (Larivière and Messier 1996). Limiting aboveground activity to nighttime may also allow Eastern Spotted Skunks to reduce temporal competition for resources with other co-occurring small carnivores such as Urocyon cinereoargenteus (Schreber) (Gray Fox), Procyon lotor (L.) (Raccoon), and Striped Skunk that are not as strictly nocturnal (Carver et al. 2011, Crooks and Van Vuren 1995, González-Maya et al. 2009, Neiswenter et al. 2010). By examining activity patterns of Eastern Spotted Skunk, we can better understand their foraging behavior and susceptibility to predation as well as improve the methodology used to monitor skunks in future studies. Based on our results, we suggest that monitoring of skunk behavior should account for effects such as temperature and moon phase, which may limit when individuals are active for observation and capture. Future research on Eastern Spotted Skunks is needed to compare activity patterns between sexes and among seasons. Additionally, activity patterns at a finer scale can be examined by equipping skunks with Global Positioning System (GPS) collars and accelerometers (Gervasi et al. 2006). Acknowledgments We thank Nicholas Sharp, Jonathan Stober, Melchisedec Adobah, Dino Alabre, Mattea Lewis, and Mandy Pearson for technical and research assistance. Funding for this project was provided by the University of West Georgia, the Friends of Talladega National Forest, and Alabama Section 6 funds. Literature Cited Carver, B.D., M.L. Kennedy, A.E. Houston, and S. B. Franklin. 2011. Assessment of temporal partitioning in foraging patterns of syntopic Virginia Opossums and Raccoons. Journal of Mammalogy 92:134–139. Crabb, W.D. 1941. Food habits of the Prairie Spotted Skunk in southeastern Iowa. Journal of Mammalogy 22:349–364. Crabb, W.D. 1948. The ecology and management of the Prairie Spotted Skunk in Iowa. Ecological Monographs 18:201–232. Crooks, K.R., and D. Van Vuren. 1995. 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