Avian community characteristics and demographics reveal how conservation value of regenerating tropical dry forest changes with forest age.

Abstract

Expansion of secondary forests following the abandonment of agriculture may have important implications for bird conservation, but few studies have examined the dynamics of this process. We studied bird use of a chronosequence of differently-aged abandoned pastures regenerating to dry forest to better understand how the value of these habitats to birds changes over time. In a five year study on Hispaniola, we recorded 7,315 net captures of 60 species of landbirds in sites that began the study at two, five, 10, and 20 years post-abandonment, and in mature native dry forest. Twenty-five species made up 97% of all net captures. Highest capture rates were in the two youngest sites. These early-successional habitats had many over-wintering Neotropical migrants; among residents, granivores and frugivores predominated. In contrast, both the twenty-year-old and mature forest sites had few migrants, more resident insectivores and omnivorous species, and a greater proportion of endemics. Age and sex ratios, body condition and site persistence suggest early successional sites were sub-optimal for most over-wintering migrants, but habitat improved with age for three migratory species; results for permanent residents varied among species. Remnant trees and understory shrubs in the agroecological matrix likely contributed to avian diversity in regenerating dry forest sites, and proximity to mature forest also likely affected the diversity and abundance of birds in regenerating habitat. Our study shows that regenerating forests do not fully compensate for loss of mature dry forest habitat, even after 24 years of regeneration; natural restoration of complex microhabitats in dry forest sites converted to agriculture may take decades or longer. The highest value of regenerating forests may be as habitat for some over-wintering Neotropical migrants, and in creating a buffer zone that enhances biodiversity conservation by re-integrating these lands into the protected tracts of mature forest needed by the islands more unique and endemic bird species.