LILLYWHITE, H.B.; ZAIDAN III, F.; University of Florida, Gainesville; University of Florida, Gainesville: Mutualism Between Birds and Snakes at Seahorse Key, Florida

Seahorse Key is a 67 ha island protected in the Cedar Keys National Wildlife Refuge as an important rookery for thousands of wading birds that nest there. Cottonmouth snakes (Agkistrodon piscivorus conanti) inhabit this same island where they are entirely terrestrial and scavenge on dead or rotting fish that are dropped or regurgitated by nesting birds. Stable isotope analyses indicate that fish are the sole or principal dietary energy source for snakes. Scavenging of fish is limited to periods of nesting activities by birds (generally April – October) and is curtailed by drought that can shorten the nesting season, reduce the number of nesting birds, and eliminate foraging by snakes that remain below ground surface to conserve water. Snakes cease to forage and retreat to underground refugia when their body water deficit increases to somewhere between a few and 12% of body mass. Thus, scarcity of water, and especially prolonged drought, can seriously impact the energetics and survival of snake populations due to combined effects on prey abundance and foraging behavior. Comparative studies of several islands within the Cedar Keys demonstrate a close correlation between the abundance of cottonmouth snakes and successful nesting of wading birds. Data further suggest the relationship between nesting birds and snakes is one of mutualism. The birds provide carrion as a food subsidy for the snakes, while the snakes, in turn, appear to deter the establishment of nest predators at the rookeries. Supported by U.S. Fish & Wildlife Service and the Disney Wildlife Conservation Fund.