POPULATION DECLINES OF THE PUERTO RICAN VIREO IN GUANICA FOREST.

Abundance of the Puerto Rican Vireo (Vireo Zutimeri) in Guanica Forest, Puerto Rico, has declined gradually over the period 1973-1996 as determined by constant effort mist netting. Concurrent studies of breeding vireos show low nesting success, primarily due to parasitism by Shiny Cowbirds (Molothrus bonariensis). This decline may reflect the rather recent entry of the cowbird into Guanica Forest during the breeding season, as other factors (vegetation change, rainfall) do not seem to explain the decline. As a single island endemic, it is important that the cause of this decline be determined so that recovery efforts can begin while the species is still moderately abundant.