SUMMARY The fluctuations of a Puerto Rican dry forest bird population were sampled by netting over a 5-year period that included drought conditions. The absence of normal May and June rains most affected the resident bird populations that breed during this period. Frugivorous species declined most sharply, while gleaning insectivores declined least. Winter resident gleaning insectivores actually increased as resident insectivores declined. It is suggested that insects may provide a scarce, but predictable, resource that attracts winter residents, and thus, in turn, restricts the breeding season of resident insectivores. Such restriction exposes breeding birds to variable early wet season conditions. The relative unpredictability of the fruit, seed and flower resource seems to limit winter residents that use these foods and releases resident members of these guilds from some of the restrictions in breeding. Despite pronounced population declines, no regular member of the Guanica Forest bird community disappeared during the drought.