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Spatial Ecology and Habitat Use of the Coachwhip in a Longleaf Pine Forest
Jennifer M. Howze and Lora L. Smith

Southeastern Naturalist, Volume 14, Issue 2 (2015): 342–350

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Southeastern Naturalist J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 342 2015 SOUTHEASTERN NATURALIST 14(2):342–350 Spatial Ecology and Habitat Use of the Coachwhip in a Longleaf Pine Forest Jennifer M. Howze1,* and Lora L. Smith1 Abstract - We examined spatial ecology and habitat use of Coluber flagellum (Coachwhip) in a 12,000-ha Pinus palustris (Longleaf Pine) reserve in southwestern Georgia from 2007 through 2008. We radio-tracked 7 Coachwhips (5 males and 2 females) for 291 to 325 days. The average 100% minimum convex polygon (MCP) home-range for all snakes was 102.9 ± 28 ha. Daily movement during the active season (April–November) varied from 28.6 to 73.6 m for males (n = 5) and from 27.5 to 95.6 m for females (n = 2). Snakes were usually associated with open-canopied pine forests and found less often in aquatic and agricultural habitats. Our results are consistent with evidence from previous studies in that Coachwhips used sites with open-forest structure and large expanses of habitat. Introduction Knowledge of how an animal uses space is vital to understanding its ecology (Gregory et al. 2001). Many factors, including habitat structure and reproduction (Gibbons and Semlitsch 2001, Gregory et al. 2001), prey availability (King and Duvall 1990, Shine et al. 2003), competition (Moore 1978), predator density (Shine and Lambeck 1985), and environmental conditions (Lillywhite 2001, Webb and Shine 1998), influence spatial ecology and movement of snakes and play a role in determining activity levels. Foraging ecology may also be an important indicator in predicting spatial-use and movement patterns for wide-ranging species. The most-common foraging modes exhibited by squamates fall within 2 general categories: sit-and-wait foragers that ambush active prey, and active foragers, like Coluber flagellum Shaw (Coachwhip), that hunt active and sedentary prey as they move through the landscape (Cooper and Whiting 2000, Huey and Pianka 1981, Mushinsky 2001, Schoener 1971, Secor 1995). The active-foraging strategy balances higher predation risk and greater energy expenditure with increased energy acquisition through high food intake (Secor 1995, Secor and Nagy 1994) and can result in species like Coachwhips potentially traveling great distances (>1 km per day) and using large home-ranges (McCartney et al. 1988, Secor 1995). The Coachwhip has an expansive geographic range that extends from North Carolina to southern Florida and west to Texas, Oklahoma, and southeastern Kansas (Conant and Collins 1998). In the Southeast, Coachwhips are strongly tied to the southeastern coastal plain, which is characterized by xeric upland habitats (Tuberville and Gibbons 2008) and was once dominated by the currently endangered Pinus palustris Mill (Longleaf Pine) ecosystem (Edwards et al. 2013). Although 1Joseph W. Jones Ecological Research Center, 3988 Jones Center Drive, Newton, GA 39870. *Corresponding author - jhowze@jonesctr.org. Manuscript Editor: Natalie Hyslop Southeastern Naturalist 343 J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 Coachwhips are not endemic to the Longleaf Pine ecosystem (Halstead et al. 2009, Johnson et al. 2007, Mitrovich et al. 2009), remnants of this once wide-ranging ecosystem likely play a significant role in the species’ persistence. Few studies (Baxley and Qualls 2009, Dodd and Barichivich 2007) have quantified spatial ecology and habitat use of Coachwhips within the Longleaf Pine ecosystem. Therefore, we present radio-telemetry data to address informational gaps on how Coachwhips use components of this important habitat in southwestern Georgia. Methods This study was conducted at Ichauway, the research site of the Joseph W. Jones Ecological Research Center in Newton, GA. The 12,000-ha site consisted mainly of second-growth Longleaf Pine savanna managed on a 2-year prescribed-fire rotation. Patches of closed-canopied Quercus spp. (oak) forests occurred primarily in isolated depressions, around seasonally inundated wetlands, and along 45 km of Ichawaynochaway Creek and the Flint River. Wildlife-food plots (comprised of Sorghum bicolor [Milo], Triticum spp. [wheat], and Zea mays [Corn]) and Longleaf Pine plantations were scattered throughout the property. The property was surrounded by center-pivot-irrigated agricultural lands. We captured snakes using 16 box-trap arrays (Burgdorf et al. 2005) located in Longleaf Pine savanna habitat with native groundcover species, including Aristida stricta Michx. (Wiregrass), Andropogon spp. (broomsedge), and Pteridium aquilinum (L.) Kuhn (Bracken Fern). We checked the traps 3 times per week from March through November in 2007 and 2008. For each snake captured, we collected snout-to-vent length (SVL), tail length, and body mass measurements and identified sex through cloacal probing. We marked captured snakes using passive integrated transponder (PIT) tags injected subcutaneously between the dorsal and ventral scales on the lower third of the body (Gibbons and Andrews 2004). We selected 5 adult male and 5 adult female Coachwhips based on size (>74 cm SVL) and sex (we attempted to maintain an equal sex ratio) and surgically implanted them with 9-g radio transmitters with an 18-month battery life (model SI-2; Holohil Systems Ltd., Carp, ON, Canada) using methods described in Reinert and Cundall (1982). We radio-tracked Coachwhips (SVL range = 134.7–160.4 cm) for 11 months, from June 2007 through April 2008. We located snakes 1–2 times per week using triangulation techniques (≥2 bearings collected) during the active season (April–November) because snakes were often moving as we tracked them. We honed in on snake locations using radio telemetry during the inactive season (December–March) when snakes were overwintering. We minimized triangulation error by discarding bearings under the following conditions if: (1) signal strength was weak, (2) the angle between locations was <45° or >135°, or (3) the sequential bearing observations were greater than 15 min apart (White and Garrott 1990, Withey et al. 2001). We recorded all snake locations (UTM coordinates) on a handheld PDA accurate to within 3 m (Garmin IQue 3600; Garmin International, Inc., Olathe, Kansas) and calculated triangulated locations using Program Locate software (Nams 2006; Pacer Computing, Tatamagouche, NS, Canada). Southeastern Naturalist J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 344 We employed ArcGIS 9.3.1 (Environmental Systems Research Institute, Redlands, CA) to create a spatial layer that included snake locations. We used Hawth’s Tools extension (Beyer 2004) in ArcGIS 9.3.1 to construct 100% minimum convex polygon (MCP; Mohr 1947) home-ranges and Home-Range Tools extension in ArcGIS 9.3.1 to calculate 95% and 50% (core) MCPs to facilitate comparison with other published studies. We used linear regression to identify if length of tracking period or number of tracking events were related to home-range size (100% MCPs). We used Hawth’s Tools extension to calculate the distance between consecutive points for each snake and standardized distance estimates by calculating daily movements (straight-line distance between consecutive points divided by the number of days between tracking events). We created a spatial-data layer using ArcGIS 9.3.1 that included unique snake locations plotted within an existing land-cover (habitat) data layer that was digitized using 1:12,000-scale color infrared aerial photography and from ground truthing observations. The land-cover layer included 4 habitat classes: (1) agriculture/scrub habitat (wildlife food plots and old fields); (2) hardwood forest (Quercus falcata Michx. [Southern Red Oak], Q. virginiana Mill. [Live Oak], Q. laurifolia Michx. [Laurel Oak], and Q. nigra L. [Water Oak]); (3) pine forest (natural Longleaf Pine savanna), Longleaf Pine plantation (sawtimber- and pole-size classes), and mixed natural pine forests (50–80% Longleaf Pine savanna mixed with oaks); and (4) aquatic habitat (isolated wetlands and Ichawaynochaway Creek). We defined the study area as a 100% MCP for all snake locations with a 500-m buffer, which we considered to include habitat available to snakes based on the daily distance Coachwhips traveled during this study (averages all <100 m). We used compositional analysis (Aebischer et al. 1993) to test for second-order (landscape level) and third-order (home-range level) habitat use (Johnson 1980). To test for habitat use at the home-range scale, we used multivariate analyses of variance (MANOVA) to compare (1) habitat use at snake locations to habitat available within home range (100% MCP), (2) habitat use at snake locations to habitat available at the core area (50% MCP), and (3) available habitat within the core area (50% MCP) to available habitat within the home range (100% MCP). To test for habitat use at the landscape scale, we compared available habitat within the home range (100% MCP) to available habitat within the study area. Results We radio tracked 7 Coachwhips (5 males and 2 females) from 291 to 325 days. Two of the 10 snakes implanted with radio-transmitters died (1 female unknown mortality, 1 female egg-bound), and a third snake was lost within the first 2 months of the study; we excluded these 3 individuals from analyses. We observed an average of 27 unique locations per snake (range = 18–31) and an average of 40 tracking events (includes locations where snakes remained in the same location during the inactive season) per snake (range = 27–47). During our sampling period from June 2007 through April 2008, snakes exhibited the greatest daily movement Southeastern Naturalist 345 J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 during June–September and the following April (Fig. 1). We observed decreased daily movement in October and November, and did not observe movement for most snakes (6 of 7) during the coldest months (December–February). Average daily movement of snakes during the active season (April–November, Fig. 1.) varied from 28.6 to 73.6 ± 27.8 m for males (n = 5) and 27.5–95.6 ± 22.1 m for females (n = 2). Six of 7 snakes had daily movements that exceeded 100 m (15.6% of active season locations), and we recorded a maximum daily movement of 224 m made by a female. Home-range size estimates were not significantly correlated with tracking period (R² = 0.10, P = 0.51) or number of tracking events (R² = 0.21, P = 0.30). Average 100% MCP home range for all snakes was 102.9 ± 28 ha (Table 1.). Male snakes had an average 100% MCP that was more than twice that of female snakes Figure 1. Average daily movement of male (n = 5) and female (n = 2) Coluber flagellum (Coachwhip) radio-tracked from June 2007 through April 2008 in Baker County, GA. Table 1. Average home-range estimates (ha) using minimum convex polygons (MCP) for 7 telemetered Coluber flagellum (Coachwhip) radio-tracked from June 2007 to April 2008 in Baker County, GA. MCP 100% MCP 95% MCP 50% All snakes Average (SD) 102.9 (28.0) 84.9 (32.0) 12.7 (9.1) Range 59.1–132.6 48.1–132.6 3.9–28.9 Male (n = 5) Average (SD) 117.9 (13) 98.2 (27.5) 12.8 (10.0) Range 113.0–132.6 58.0–132.6 3.9–28.9 Female (n = 2) Average (SD) 65.2 (9) 51.7 (5.0) 12.3 (10.1) Range 59.1–71.3 48.1–55.2 5.2–19.4 Southeastern Naturalist J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 346 (males: 117.9 ± 12.8 ha, females: 65.2 ± 8.6 ha). Average 50% MCP core areas were similar in size for the following: all snakes: 12.7 ± 9.1 ha, males: 12.8 ± 10.0 ha, and females: 12.3 ± 10.1 ha. Coachwhips used habitats relative to their availability at the landscape scale (F = 2.75, P = 0.21), home-range scale (F = 0.06, P = 0.98), and the core-area scale (F = 4.42, P = 0.13); however, composition of habitat within the core home range differed significantly from that of the 100% MCP home range (F = 16.3, P = 0.02). Specifically, the proportion of pine forests in core areas was greater than expected based on availability within the 100% MCP, whereas the proportion of aquatic and agricultural habitats in core areas were less than expected (Fig. 2). Discussion Studies have suggested that large-bodied terrestrial snakes require extensive habitat to maintain their populations (Dodd and Barichivich 2007, Hyslop et al. 2014, Mitrovich 2006). Previous research at our study site found that average homeranges for large-bodied sit-and-wait foragers, including Pituophis melanoleucus Daudin (Pinesnake; 100% MCP = 59.2 ha; Miller et al. 2012), Lampropeltis getula L. (Eastern Kingsnake; 100% MCP = 49.5 ha; Linehan et al. 2010), and Crotalus adamanteus Palisot de Beauvois (Eastern Diamondback Rattlesnake; 100% MCP = 24.6 ha; Hoss et al. 2010), were smaller in comparison to that of the Coachwhip. Figure 2. Average proportional core-habitat use by Coluber flagellum (Coachwhip) relative to availability (home range) in Baker County, GA. Southeastern Naturalist 347 J.M. Howze and L.L. Smith 2015 Vol. 14, No. 2 Coluber constrictor L. (North American Racer), a congener of the Coachwhip that exhibits a similar active-foraging mode but a smaller body size, reportedly has smaller average MCP home ranges (11.45 ha and 12.2 ha, respectively; Klug et al. 2011, Plummer and Congdon 1994) than that of the Coachwhip. Another active forager, Drymarchon couperi Holbrook (Eastern Indigo Snake), one of the largest native snakes in the Southeast, used larger average home-ranges (100% MCP > 340 ha) than did Coachwhips in similar habitats (Hyslop et al. 2014). Therefore, a combination of an active-foraging strategy and a large body size may be important in explaining the larger spatial requirements for snakes like Coachwhips and Eastern Indigo Snakes. We observed long-distance daily movements exceeding 100 m for 6 of 7 snakes during the active season. We assume that we missed some additional long-distance movements in our study because we tracked snakes once per week and we were unable to sample during May, when Coachwhips were most active at our study site (J.M. Howze, unpubl.data). Additionally, we calculated our distance estimates as straight-line measurements between locations, which likely underestimated the actual length of paths traveled by snakes. Nonetheless, our findings, along with research on Coachwhips in Texas (100% MCP = 70.4 ha; Johnson et al. 2007), California (100% MCP = 136.4 ha; Mitrovich et al. 2009), and Florida (100% MCP = 183 ha [males], 102 ha [females]; Halstead et al. 2009) support the body of evidence describing the large spatial requirements necessary for this species across its range. Secor (1995) found that these large home-ranges reflected frequent longdistance movements by Coachwhips. Previous studies have reported that Coachwhips were found in a variety of open-canopy, xeric, southeastern forest types including Longleaf Pine, scrub, oak savanna, sandhills, and pine flatwoods (Dodd and Barichivich 2007, Halstead et al. 2009, Johnson et al. 2007, Tuberville and Gibbons 2008). Our data suggested that Coachwhips used pine forest more often in their core areas and were less likely to use aquatic and agricultural habitats, suggesting that habitat structure might be an important variable in explaining habitat selection in Coachwhips. Further evidence provided by Baxley and Qualls (2009) described a positive correlation between Coachwhips and xeric open-canopy areas within Longleaf Pine habitats. Coachwhip foraging strategy may explain a propensity for open-forest structure. They are visual predators, and areas with sparse vegetation may be helpful for hunting (Ernst and Ernst 2003) lizards (their primary prey) and small mammals (Halstead et al. 2008, Hamilton and Pollack 1956, Secor 1995). Furthermore, Coachwhips use structural features of open-canopy habitats like rotting pine stumps, root holes, and animal burrows to forage for prey, escape predators, and regulate body temperature during thermal extremes (Dodd and Barichivich 2007, Ernst and Ernst 2003, Gentry and Smith 1968, Secor 1995, Secor and Nagy 1994, Tuberville and Gibbons 2008). Forest-management practices such as prescribed fire and thinning, which maintain an open-canopy structure, and the protection of contiguous habitat may help to provide appropriate habitat for Coachwhips in the Southeast. Southeastern Naturalist J.M. Howze and L.L. 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