Human Activity Continues to Threaten a Federally Listed Snake

The eastern indigo snake (Photo 1), Drymarchon couperi, is a large, nonvenomous snake native to southeastern coastal plain areas, most commonly in southeastern Georgia and peninsular Florida. The species was federally listed as threatened in 1978 and has been the focus of recent conservation efforts. These snakes are long-lived and reach sexual maturity relatively late at 3-4 years of age (Hyslop et al. 2012).

Photo 1: An eastern indigo snake in Florida; photo originally taken by Todd Pierson and made available via the Florida Museum: Florida Snake ID Guide. Link: https://www.floridamuseum.ufl.edu/florida-snake-id/snake/eastern-indigo-snake/

The eastern indigo snake has primarily been threatened by habitat fragmentation and degradation, as seen by the fact that the longleaf pine and wiregrass sandhills that these snakes reside in have faced an area decline of over 97% since European colonization (Hyslop et al. 2012). and Breininger et al. found that over 50% of known eastern indigo snake mortalities within their 2012 study were due to human activity along roadways. The eastern indigo snake’s size means it is rarely preyed upon, so roads and human activities are a common source of mortality for this species (Breininger et al. 2012).

Figure 1: The top figure shows the annual survivability of the eastern indigo snake in three different areas (conservation core, conservation near roadway, and suburb) and the bottom figure shows the probability of encountering an eastern indigo snake in the same three areas. Figure courtesy of Breininger et al., 2012.

Beyond the increase threat to the survival of this snake due to roadways, urbanization is causing the home range to become increasingly restricted. Their northern range had previously been limited in part due to their use of Gopher Tortoise burrows as a source of protection from weather events and predators or as a breeding and nesting site (Hyslop et al. 2012). In more recent years, increased urbanization has led to a decrease in habitat diversity and home range size. In response to habitat fragmentation, it is very common to see animals increase their home range size, however eastern indigo snakes have had the opposite reaction. The mean area used by this species has decreased and the reason behind the change is still unclear. The leading hypotheses are that the snakes in suburbs moved less because they were easily able to find prey, the snakes outside of the suburbs have purposefully decreased their range and altered behavior in order to avoid roadways, or that the eastern indigo’s ability to take over den sites and feed on a wide variety of prey has allowed the snake to occupy areas uninhabitable to other species (Breininger et al. 2011). The exact reasoning for the alterations in the eastern indigo snake’s behavior and home range may be unknown, but all current hypotheses have important conservation implications and work is continuing to be done to ensure the survival of this species.

References:

Breininger, D. R., M. J. Mazerolle, M. R. Bolt, M. L. Legare, J. H.Drese, and J. E. Hines, 2012. Habitat fragmentation effects on annual survival of the federally protected eastern indigo snake. Animal Conservation 15: 361-368.

Breininger, D. R., M. R. Bolt, M. L. Legare, J. H.Drese, and E. D. Stolen. 2011. Factors influencing home-range sizes of eastern indigo snakes in central Florida. Journal of Herpetology 45: 484-490.

Hyslop, N. L., D. J. Stevenson, J. N. Macy, L. D. Carlile, C. L. Jenkins, J. A. Hostetler, and M. K. Oli. 2012. Survival and population growth of a long-lived threatened snake species, Drymarchon couperi (Eastern Indigo Snake). Population Ecology 54: 145-156.

Pearson, T.,  2021. Eastern Indigo Snake. Florida Museum of Natural History. https://www.floridamuseum.ufl.edu/florida-snake-id/snake/eastern-indigo-snake/

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