Avian Predation on Anolis Lizards in the Northeastern Caribbean: Inter‐Island Contrast

This paper presents results of a field study of avian predation on Anolis lizards on islands in the northeastern Caribbean, addressing the question of what causes annual fluctuation in lizard abundance. The two main potential avian predators, the Pearly—eyed Thrasher (Margarps fuscatus) and the American Kestrel (Falco sparverius), were studied on three adjacent islands in the northern Lesser Antilles: Anguilla, St. Martin, and St. Eustatius. Anoles on Anguilla were found to be quantitatively unaffected by avian predation; thrashers there did not eat vertebrates, and the kestrel density was too low to have significant impact on the lizard population. In contrast, thrashers in moist habitat on St. Martin ate vertebrates including anoles, and thrasher predation potentially accounted for the anole decline to the dry—season abundance low. Additionally, an unanticipated thrasher niche shift was discovered. Thrasher body size and diet appear to be related to the abundance of a congeneric species, M. fuscus. On Anguilla, where M. fuscus was absent, M. fuscatus was smaller and had a non—vertebrate diet. On St. Eustatius, M. fuscus was abundant while M. fuscatus was larger and preyed on anoles. M. Fuscus was rate on St. Martin, where M. fuscatus had an intermediate body size and a diet comparable to that on St. Eustatius.