Vines and canopy contact: a route for snake predation on parrot nests

Abstract

Ornithologists have hypothesized that some tropical forest birds avoid snake predation by nesting in isolated trees that do not have vines and canopy contact with neighbouring trees. Here we review two complementary studies that support this hypothesis by demonstrating (1) that an abundance of vines and an interlocking canopy characterized Jamaican Black-billed Parrot Amazona agilis nest-trees that failed due to chick loss, presumably to snakes, and (2) that such trees were used preferentially by an arboreal snake congeneric to the snake implicated in the parrot losses. Evidence strongly suggested that losses of nestling Black-billed Parrots were due in substantial part to predation by the Jamaican (yellow) Boa Epicrates subflavus (Boidae). Studies of the closely related Epicrates inornatus on Puerto Rico revealed that trees used by boas had more vine cover and more crown or canopy contact with neighbouring trees than did randomly selected trees. Moreover, the boas had relatively large home ranges and were most active during March to July, which corresponds with the breeding season of parrots as well as other bird species. We suggest that nest failure due to snakes may be reduced in endangered bird species through isolating the nest-tree by eliminating vines and canopy contact with neighbouring trees and shrubs and by placing barriers on the nest-tree trunk.