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.