Alternative Foods of a Diet Specialist, the Snail Kite

Abstract

Although Snail Kites (Rostrhamus sociabilis) in Florida [USA] and Venezuela fed mostly on Pomacea snails, I documented three alternative foods. In Florida, kites fed on five species of small turtles, but especially on Sternotherus odoratus and Kinosternon bauri. During the height of a drought, one kite in Florida fed on a small aquatic snail (Viviparus georgianus) for 5 weeks. In Venezuela, freshwater crabs (Dilocarcinus dentatus) made up on average 10% of the Snail Kite's diet, but more than 25% during September and October. Kites consumed alternative foods with techniques that resemble snail-eating behavior, such as entering a turtle's body cavity by piercing the only leg shaped like a snail operculum. Handling times for turtles (76 min) and crabs (5.4 min) were much longer than for Pomacea snails (1.5 min). Viviparus snails required approximately one-third less handling time but contained one-fifth less body mass than Pomacea snails. Handling time (30 s) for V. georgianus did not differ between the Snail Kite and the Boat-tailed Grackle (Quiscalus major), a diet generalist. These findings are related to the factors that reinforce diet specialization and the ecological conditions that promote diet diversification in specialists. Like Pomacea snails, alternative foods have shells or carapaces and move relatively slowly. Alternative foods are probably less profitable than Pomacea snails, except for large crabs. Although crabs were regularly eaten by kites in Venezuela, turtles and Viviparus snails were eaten in Florida only during times of food scarcity.