Home > Science Seminar > Spring 2006 Seminar Schedule > Ecology of Birds and Snakes
The Science Seminar Series: February 23, 2006
Ecology of Birds and Snakes on Gulf Coast Islands
Dr. Harvey Lillywhite, Department of Zoology
University of Florida
Gainesville, FL
Room 1011 Biology/Chemistry BuildingTime: 4:00 -5:00pm
Historically, Gulf Coast islands have provided important nesting refugia for thousands of wading birds, including pelicans, cormorants, ibis, herons and egrets. Cottonmouth snakes (Agkistrodon piscivorus conanti) inhabit these same islands where they are entirely terrestrial and scavenge on dead or rotting fish that are dropped or regurgitated by nesting birds. Unlike many other island systems in which birds and snakes associate, cottonmouths are not direct predators on the birds but depend on them for input of fish. 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 prohibit foraging by snakes. Snakes cease to forage and retreat underground when their body water deficit increases to somewhere between 12% and 16% 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 Florida's Cedar Keys 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 predators on avian nests. Thus, on islands having large bird rookeries and numerous cottonmouths, there are no raccoons, no arboreal snakes, and introduced rats appear to be less abundant than in areas without snakes. Eastern diamondback rattlesnakes (Crotalus adamanteus) also occur on these same islands but in far lesser abundance where cottonmouths are numerous at bird rookeries. The success of cottonmouths in association with avian rookeries possibly precludes the establishment of rattlesnake populations, whereas the latter can be dominant on other islands.