Discussion
The spatial ecology of the Timber Rattlesnake has been well studied in the northeastern and central parts of its distribution, but little is known of southern populations. Because temperature, habitat type, and prey composition and abundance dictate many aspects of reptile behavior, populations of conspecific species may exhibit behavioral differences across latitudinal and elevational gradients. Waldron et al. (2006a) indicated that Timber Rattlesnakes within a population in South Carolina had smaller mean annual home range sizes than conspecific populations in Virginia and New Jersey, with the New Jersey population having the largest home range. Furthermore, Mohr (2012) found Timber Rattlesnakes within a population in northeastern South Carolina moved shorter distances throughout the active season than populations previously studied at higher latitudes. Our study shows the same pattern of decreasing home range size from north to south.
Our analyses found that the annual home range sizes and average distances moved between successive relocations of males in the current study were statistically equal to those of non-gravid females (Figs. 6 and 7). Mohr (2012) also found that the average distances moved between relocations did not differ among sex within a population in the South Carolina mountains, but most other studies found male Timber Rattlesnakes had larger home range sizes and moved further distances than gravid and non-gravid female snakes (Reinert and Rupert 1999, Reinert and Zappalorti 1988, Rudolph and Burgdorf 1997, Sealy 2002, Waldron et al. 2006a, Waldron et al, 2006b). It is not clear why home range sizes of snakes in our study’s population are so small, but prey density, habitat quality, climatic factors, body size, and reproductive female density have all been shown to affect home range sizes (Bjorneraas et al. 2011, Carrasco-Harris et al. 2020, Harestad and Bunnel 1979, Lendrum et al. 2014).
Because sit-and-wait predators, like Timber Rattlesnakes, will remain concealed in a location until a prey item comes within a close enough proximity to capture it, or until the probability of obtaining a prey item decreases enough to warrant moving to a new location, they may rely on high quality foraging habitats to gain energy (Schoener 1971). Both prey density and suitable microhabitat availability may affect an area’s foraging quality (Beaupre 2008, Clark 2004a, Clark 2004b, Reinert et al. 2011). Many populations of Timber Rattlesnakes travel long distances to get from their winter den to summer foraging grounds. The transient habitat in between the den and foraging grounds may be suitable for thermoregulation, but not foraging (Brown 1992). Temperate rattlesnakes, like many other ectotherms, must obtain enough energy from food intake to satisfy energy requirements before temperatures become too low for activity. An increase in the amount of time a snake spends traveling between foraging sites may result in a net decrease in energy at the end of the active season. If energy requirements are not met, the snake may not be able to maintain its current lifestyle (Schoener 1971). During this study, there was an absence of long movements away from hibernacula in the spring. In fact, snakes were observed foraging within 2 m of known hibernacula. This likely indicates that prey availability and foraging habitat quality are high enough that snakes in this population have no need to travel long distances to foraging sites. Individuals may only have to travel far enough that competition between conspecifics is low. This could also play a role in the small home range sizes of snakes in this population.
The study area is mostly a contiguously forested landscape, but there are two major highways that run through it, bordering most of the study sites (Fig. 3). There are also small patches of commercial and residential development within the area. Roads may act as physical barriers that prevent snakes from crossing them (Andrews and Gibbons 2005) and as genetic barriers that prevent neighboring populations from exchanging genetic material (Clark et al. 2010). Species hesitant to cross open spaces, such as large, heavy-bodied snakes, like the Timber Rattlesnake, are especially susceptible to road barriers (Andrews and Gibbons 2005).
Every home range within this study was bordered by a paved or gravel road. Five of the snakes within this study crossed small gravel roads, but none crossed paved roads throughout the entire study. This could indicate either, the paved roads were acting as impervious barriers, or the snakes did not travel across these roads because the habitat, prey density, or some other variable across the road is of lower quality. Site B, Site F, and the road adjacent to these sites are located on a narrow natural levee formed by an abandoned distributary of the Mississippi River, providing a small area of slightly higher elevation than the surrounding areas. The land directly across the road is forested, but abruptly turns to marsh and open water. The habitat across the road adjacent to Site M has been clear cut or developed, and site H is bordered by water and commercial development on all sides. These habitats may not be suitable for Timber Rattlesnakes, so an attempt to cross the road may not be profitable for snakes in this population.
In our study, we found that seasonal home ranges and movements of male and female snakes were not statistically different from each other, but males did have larger average home range sizes and movements than females in September-November (Fall) (Fig. 6 and 8). These increases in home range size and movement seemed to coincide with the breeding season, which took place from early July until the end of November. An increase in home range size and movements is common for male snakes searching for receptive females in other populations of the Timber Rattlesnake. Even though there was an increase in home range size for males during the breeding season in southeastern Louisiana, it was not as drastic as found in other populations (Anderson 2015, Lind and Beaupre 2015, Reinert and Zappalorti 1988, Waldron et al. 2006b). Longer term studies with larger sample sizes are needed to retest these results.
Currently, there are many gaps in information regarding geographical differences in behaviors and life history traits of Timber Rattlesnake populations. Understanding the causes and effects of these differences at a local level may help mitigate some of the fallacies of conservation efforts that exist from extrapolating information from studies of populations that are spatially distant. This baseline study of the spatial ecology of a population of Timber Rattlesnakes in southeastern Louisiana is another step towards a better understanding of this species.