Trophic Niche And Home Range Of An Insular Pit Viper Following Loss Of Food Resources

Investigations of the response of wild populations to natural ecological disturbances can provide insights into the ability of animals to respond to ever-increasing and intensifying stressors. Seahorse Key is a continental island in the Gulf of Mexico that has been an important rookery site for several species of colonially nesting waterbirds. Resident cottonmouth snakes, Agkistrodon conanti, feed heavily on fish carrion provided by nesting waterbirds. Unexpectedly in 2015, the entire waterbird colony abandoned Seahorse Key and has not returned since. We used stable isotopes and radio-telemetry to test hypotheses related to the response of the trophic niche and size of home range of insular cottonmouths following the loss of bird-provided food resources. We found that stable isotope values of carbon (delta C-13) decreased while nitrogen (delta N-15) values increased between the pre- (n = 188) and post-abandonment (n = 48) periods. The observed changes in stable isotope values correspond to a reduction in feeding on marine fish to terrestrially derived food resources and were also affected by body size and age class. Home range calculated from snakes tracked using radio-telemetry showed no significant changes between pre- and post-abandonment periods. These data corroborate earlier studies to indicate that cottonmouths on Seahorse Key have not effectively compensated for sudden substantial loss of food resources. This insight has implications for the conservation and management of populations with episodic components of food webs, especially in relation to ecological disturbance.