JOHNSTON: CAYMAN ISLAND AVIFAUNA


fluence the resident species very little, chiefly because the wintering
forms usually occupy different feeding niches than the residents. That
is, migrants rely upon a food resource not fully exploited by the residents,
a feature previously noted in tropical regions by Morel and Bourliere
(1962) and Willis (1966). On the other hand, migrants in the Caymans
do not necessarily favor secondary habitats or disturbed areas; hence,
they do not conform to the "irregularity principle" of Willis (1966)
except with reference to a supposed abundant winter food supply.
Nevertheless, the wintering birds, many of which are insectivorous, prob-
ably do play a significant trophic role in controlling insect populations.


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1975