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Eastern Kingsnake (Lampropeltis getula getula) Home Ranges Exhibit Limited Overlap
David A. Steen and Lora L. Smith

Southeastern Naturalist, Volume 8, Number 3 (2009): 553–558

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2009 SOUTHEASTERN NATURALIST 8(3):553–558 Eastern Kingsnake (Lampropeltis getula getula) Home Ranges Exhibit Limited Overlap David A. Steen1,* and Lora L. Smith2 . Abstract - In the course of conducting a radio-telemetry study of Lampropeltis getula getula (Eastern Kingsnake) within a ca. 3000-ha area in southwestern Georgia, we observed that adjacent home ranges of individuals infrequently overlapped. To quantify this overlap, ten interactions were compared; male/female overlap averaged 25%, while male/male overlap averaged 13%. Although we lack corroborative data, the limited overlap we observed is consistent with what would be expected from a territorial animal. Introduction Wildlife species often maintain territories that they defend from conspecifics (Maher and Lott 2000). These territories typically function to control access to a limiting resource, such as breeding opportunities or prey, resulting in an increase in an individual’s survival and reproductive success. The extent of the area defended may vary and does not necessarily encompass an individual’s entire home range (e.g., Kerr and Bull 2006). In addition to controlling resource access, social animals may maintain territories to enforce dominance structure. One of the primary methods of establishing whether an animal maintains a territory is by examining the spatial distribution of its movements in relation to conspecifics. Although the majority of territorial behavior has been observed in birds and mammals (Burt 1943, Nice 1941), lizards are known to establish and actively defend territories as well (e.g., Polychrotidae; Evans 1938, Maher and Lott 2000). Within this group, low home-range overlap is interpreted to be consistent with territoriality (Rose 1982). Limited data on territoriality have been reported for other squamates, (i.e., snakes; Gregory et al. 1987); however, recent studies have noted non-overlapping home ranges (Rodríguez-Robles 2003, Webb and Shine 1997). In the course of radio-tracking Lampropeltis getula getula L. (Eastern Kingsnakes) to determine home-range size and habitat use, we observed that adjacent home ranges of individuals infrequently overlapped. Herein, we quantify home-range overlap among adult male and female Eastern Kingsnakes. Materials And Methods Study Area We conducted this research at Ichauway, a 12,000-ha research site of the Joseph W. Jones Ecological Research Center, ca. 16 km south of Newton, 1Auburn University, 331 Funchess Hall, Auburn, AL 36849. 2Joseph W. Jones Ecological Research Center, Route 2, Box 2324, Newton, GA 39870. *Corresponding author - DavidASteen@gmail.com. 554 Southeastern Naturalist Vol. 8, No. 3 Baker County, GA. We collected snakes within a 2897-ha portion of the property bordered by a paved road to the south, and intensive agriculture to the north and east. The area is predominantly Pinus palustris Miller (Longleaf Pine) forest with an Aristida stricta Michaux (Wiregrass) ground cover. Radio-telemetry From April 2005 through September 2006, we captured kingsnakes either by hand or in snake-trap arrays modified from Burgdorf et al. (2005). All snakes were measured for snout–vent length (SVL) and body mass (g), PIT-tagged, and sexed by cloacal probing. Twelve adults (10 males and 2 females) were surgically implanted with SI-2 radio transmitters (Holohil Systems Ltd., Carp, ON, Canada) that weighed 9 g (Reinert and Cundall 1982). Snakes were located approximately once a week, and locations were recorded with a GEO3 Global Positioning System (GPS, Trimble Navigation, Ltd., Sunnyvale, CA; accuracy ± 1–5 m). Home-range size was calculated using the minimum convex polygon method (MCP; Mohr 1947, Row and Blouin-Demers 2006) and Hawth’s Tools (Beyer 2004) in ArcMap 9.1 (ESRI). Because not all snakes were monitored over the same time period, we calculated MCP home ranges based only on points collected while both snakes within a particular comparison were being monitored (i.e., home ranges overlapped temporally as well as spatially). Home-range overlap To determine the extent of MCP overlap, we used a modified equation of a simple ratio (Ginsberg and Young 1992): [(n1 + n2) / (N1+N2)] x 100, where n1 and n2 represent the number of locations that overlapped an adjacent home range for each of two individuals and N1 and N2 represent the total number of locations for those individuals (Gehrt and Fritzell 1998). We quantified overlap only for snakes with adjacent and overlapping home ranges. Results Snakes varied in size and body mass (872 to 1341 mm SVL and 285 to 830 g, respectively). Transmitter mass was always <3.2% of a snake’s mass. Snakes were held in captivity a mean of 47 days from the original capture date before being released at the capture site. The relatively long holding time was a necessary consequence of having the surgeries completed by a qualified veterinarian. Snakes were monitored in the field for periods ranging from 222–711 days (mean = 376). Two snakes were excluded from the analysis because they were isolated from other tagged kingsnakes (home ranges were >200 m from the next nearest kingsnake home range). The 10 kingsnakes (8 males, 2 females) with overlapping home ranges were involved in 10 potential interactions. Home-range overlap ranged from 1.8 to 49% for all snakes 2009 D.A. Steen and L.L. Smith 555 (Table 1). Male/male overlaps (n = 6) averaged 13%, whereas male/female overlaps (n = 4) averaged 25% (Table 1). Discussion There is no minimum threshold of home-range overlap that would indicate an organism is territorial (Maher and Lott 1995). In addition, there are a limited number of studies on snakes with which to compare our results. With the exception of three male Pituophis catenifer (Blainville) (Gopher Snakes) that had non-overlapping home ranges (Rodríguez-Robles 2003), and male Hoplocephalus bungaroides (Schlegel) (Broad-headed Snakes), which maintained exclusive areas (Webb and Shine 1997), there is little spatial evidence for snake territoriality. In contrast, a number of studies have documented home-range overlap between snakes (Macartney et al. 1988), although the amount of overlap is generally not reported. The analysis we used to calculate home-range overlap is a standard technique recently used to examine territoriality and space-use exclusivity in mammals (e.g., Chamberlain and Leopold 2005, Gehrt and Fritzell 1998). There are more sophisticated home-range estimators than MCP which incorporate an animal’s utilization distribution (Fieberg and Kochanny 2005). However, snakes, as ectotherms, experience long periods of relative inactivity, particularly in temperate zones. This behavior can exert substantial infl uence on these estimators (Row and Blouin-Demers 2006); therefore, we chose to compare MCP overlap. Eastern Kingsnake home ranges within the same general area had little overlap, suggesting that the snakes may maintain relatively exclusive areas. Table 1. Total number of locations for individual kingsnakes and number of overlapping points within adjacent home ranges (ten pairings). Female codes are italicized. Simultaneous Individuals OverlapA TotalB Overlap Total % Overlap tracking days Male-female 1113-2225 36 105 25 103 29.33 555 5209-2225 3 36 0 38 4.05 222 4B1E-4937 24 50 26 52 49.02 272 701E-4937 11 36 5 52 18.18 272 Mean 25.15 Male-male 5803-0258 4 56 10 64 11.67 333 586E-0001 5 55 11 48 15.53 267 586E-4B1E 1 56 1 50 1.89 281 4B1E-0001 8 54 34 54 38.89 316 5209-1113 0 36 2 37 2.74 222 701E-4B1E 5 43 2 56 7.07 300 Mean 12.96 ANumber of snake locations recorded within the home range of the other individual within a particular pairing. BTotal number of locations recorded for an individual snake. 556 Southeastern Naturalist Vol. 8, No. 3 The MCP home ranges included all outlying points. Therefore, our estimate was a conservative one, as territorial animals are more likely to actively exclude conspecifics from only a portion of their home range. Male-male combat in vertebrates is thought to be associated with territory defense, social rank establishment, or obtaining access to females. Although combat is common among mammals, only 6% of snakes have been documented to partake (Schuett et al. 2001), including kingsnakes (Carpenter and Gillingham 1977, Krysko et al. 1998). Male-male combat among snakes is attributed to competition for access to females (Schuett et al. 2001), although male kingsnakes have been observed fighting in the absence of females (Carpenter and Gillingham 1977) and at a time of year (February; Krysko et al. 1998) potentially outside the breeding season (Knepton 1951; but see Krysko 2002, for a contrasting view). An alternative explanation is that male-male combat in snakes is a territorial behavior, rather than competition for access to females (Lowe 1949). Although there was limited home-range overlap among all 10 kingsnakes in our study, male/male overlap was approximately half that of male/female overlap. This suggests that if kingsnakes are territorial, the behavior may be relaxed in intersexual interactions, a finding consistent with Webb and Shine (1997). Our original study was not designed to address behavioral questions, and we readily acknowledge that we did not collect the data necessary to confirm territoriality in kingsnakes. By definition, a territory is fixed over time, territorial species exhibit behavior that results in escape or avoidance behavior of conspecifics, and through these behaviors the area they inhabit becomes exclusive (Brown and Orians 1970). Ideally, a study to determine whether kingsnakes are territorial would include a larger sample size and snakes would be tracked more frequently over a longer time period. Furthermore, on occasion we observed non-tagged kingsnakes within the home ranges of radio-tagged individuals, which is inconsistent with the hypothesis that kingsnakes inhabited entirely exclusive areas. Nonetheless, recent studies have documented seemingly novel social behaviors in snakes (Fitzgerald et al. 2002, Shine et al. 2005), and based on the results of our study, kingsnakes may be appropriate subjects to further investigate these and other behaviors. Acknowledgments All required state and federal permits were obtained. Funding for the project was provided, in part, by the Florida Fish and Wildlife Conservation Commission’s Wildlife Legacy Initiative program and the US Fish and Wildlife Service’s State Wildlife Grants program (Grant # SWG 05-020, Agreement #060010). L.M. Conner provided statistical advice and J.C. Brock assisted with GIS. A.M. Heupel, S.C. Sterrett, S.A. Miller, E.P. Hill, E. Brown, K. McKean, J. Linehan, S. Jones, and G.J. Miller conducted fieldwork associated with this study. T.M. Norton, DVM performed transmitter implant surgeries. E.P. Cox assisted in obtaining references. S. Hoss, S. Graham, C. Guyer, K. Barrett, J. Steffen, V. Johnson, C. Romagosa, J. 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