Thursday, January 9, 2014

Indigo Snakes & Gopher Tortoises in southern Georgia

The southeastern Coastal Plain is a center of reptile and amphibian diversity in the United States with habitat loss the primary cause of most herpetofaunal declines. Contributing to these declines has been the loss of the once dominant longleaf pine (Pinus palustris)–wiregrass (Aristida stricta) habitats, which historically covered about 30 million ha of the southeastern Coastal Plain prior to European settlement. At present, only about 2% of this habitat remains, and what does remain is in isolated fragments. The eastern indigo snake (Drymarchon couperi) is a wide-ranging predator closely associated with this xeric upland longleaf pine–wiregrass habitat, a habitat often referred to as sandhills. Also associated with this habitat is the gopher tortoises, Gopherus polyphemus. This association is especially pronounced in the northern portions of the species' range in south Georgia and northern Florida. Indigo snake populations have been in decline since it was federally listed in 1978. These declines are primarily attributed to habitat loss and degradation caused by development, fire exclusion, agriculture, and conversion of native longleaf pine habitats to commercial plantations of off-site pine species.

In a new paper, Hyslop et al. (2014) examine the needs associated with the eastern indigo snake in Georgia, including spatial and habitat requirements. In order to determine if the eastern indigo snakes maintained definable home ranges, to estimate annual and seasonal home range sizes and describe movements within home ranges, to examine ecological factors associated with intraspecific home range size variation, and to quantify habitat use and seasonal variation in use.

The authors radiotracked 32 eastern indigo snakes from 2002 to 2004 on Fort Stewart Military Installation and adjacent private lands in Georgia. The annual home range size varied from 33 ha to 1,528 ha.and individual home range size was most influenced by sex (males with larger home ranges) followed by body size. A ompositional analysis of habitat use suggested positive selection for wetland, evergreen forest, and pine-hardwood (mixed) forest, with an avoidance of roads and deciduous forests. Seasonally, indigo snakes used the highest diversity of habitats as they moved from xeric uplands (sandhills) in winter and early spring to wetlands and uplands other than sandhills in summer; however, snakes continued to use sandhill habitats in 35–58% of locations seasonally with gopher tortoise burrows throughout the warmest months. In Georgia, management and conservation of the eastern indigo snake should include conservation of large tracts of undeveloped land, containing a matrix of xeric uplands with suitable underground shelters and adjacent wetland habitats. The entire article is available on-line.

Citation
Hyslop, N. L., Meyers, J. M., Cooper, R. J. and Stevenson, D. J. (2014), Effects of body size and sex of Drymarchon couperi (eastern indigo snake) on habitat use, movements, and home range size in Georgia. The Journal of Wildlife Management, 78: 101–111. doi: 10.1002/jwmg.645

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