Effects of tropical forest fragmentation on ecology and conservation of migrant and resident birds in lowland Costa Rica

Decades of forest loss throughout Central America have dramatically changed the amount and configuration of winter habitat available for Neotropical-Nearctic migrant songbirds and breeding habitat for resident birds. The overall objective of my research was to understand the value of forest fragments to a diverse group of rainforest birds that depend on lowland tropical rainforest for their survival at one part or all of their annual cycle. Using both intensive research methods on a migrant songbird and extensive survey methods for eight species of resident forest birds, results show that in general, remaining forest fragments of the Sarapiqui region provide important habitat for all species studied, to varying degrees. For the wintering Wood Thrush, Hylocichla mustelina , I surveyed forest fragments of different sizes, and assessed the proportion of the population wintering outside of protected forest reserves. Fragmentation effects on wintering Wood Thrush were further studied by comparing over-winter survival, territorial fidelity, home range sizes, population structure and indices of body condition and fitness, for birds in forest fragments versus intact forest. Wood Thrushes were detected in all surveyed forest fragments > = 1 ha, and it was estimated that 80% of the population winter in forest fragments outside of protected reserves. Forest fragmentation affected sex ratios, with female Wood Thrush constituting 60% of birds sampled in small fragments (< 20 ha), 25% in large (> 200 ha), and 35% in continuous forests. Widespread presence even in fragments as small as 1 ha, along with evidence of female-biased sex ratios in small fragments, may imply that available habitat for wintering Wood Thrushes is saturated. For eight species of resident birds, we quantified changes in species abundance and patch occupancy in forest fragments that exist across a continuum of fragmentation, isolation and remaining forest cover. We detected all eight species within at least a subset of the fragments. The most abundant species, an understory wren, Henicorhina leucosticta , was observed in all 30 fragments. Two other common species, Mionectes oleaginous and Myrmeciza exsul were also found in a majority of surveyed fragments, a rather unexpected result. Abundances of two species, Pipra mentalis, a manakin, and Thamnophilis atrinucha, an antshrike, declined or the species disappeared entirely in fragments with decreasing patch size, isolation from a source, and low surrounding forest cover values. R. sulfuratus abundance was not significantly associated with any of the predictor variables. However, 4 of 6, or 67 % of the fragments lacking this species were < 25 ha. For R. swansonii, the largest toucan in the study region, highest abundances were associated with fragments embedded within areas of higher percent forest cover. Despite our predictions that species within the same foraging guild, or those with other shared life history strategies, would respond similarly to fragmentation, we found that species responded individualistically.