Annual Variation in Birds and Plants of a Tropical Second-Growth Woodland

Abstract

We examined effects of successional changes in vegetation on bird species found in a young second-growth woodland in Costa Rica over a four-year period (1985-1988). Significant changes in vegetation structure and plant composition occurred: numbers of small (2-5 cm dbh) trees, woody shrubs, and lianas increased, as did canopy cover; herbaceous shrubs declined in abundance. Total numbers and species of plants producing flowers pollinated by hummingbirds or fruits eaten by birds did not change, but significant changes were noted in fruit production of individual plant species. Overall capture rates of birds in mist nets did not vary significantly among years but significant changes were noted for individual species. Several bird species characteristic of mature forest habitat first appeared in second-growth woodland during latter years of the study; other species, more dependent on early successional habitats, decreased in abundance or disappeared entirely from our study plot. Diets of some fruit-eating birds changed over time, apparently in response to changes in abundance of different fruit species. This study suggests that changes in plant and bird populations may be relatively rapid in tropical second-growth habitats. Such results have important implications for conservation; a range of successional stages may be necessary to support the full complement of bird species that can occur in a given area.