An experimental approach to evaluating the role of epiphytes in habitat selection of birds in coffee plantations

In tropical forests, particular habitat features such as epiphytic plants have been shown to have a major impact on the distribution of bird.  However, the role of such features in habitat selection by individuals and its demographic consequences has not been established at the species level. Understanding the mechanisms of habitat selection requires experimental manipulation and detailed estimation of the response of animals through changes in movement patterns and demographic success, such as survival.  Such studies have not been conducted in natural tropical forest, perhaps because of high habitat heterogeneity, high species diversity, and low abundances of potential target species. Agroforests provide a good model system for beginning to understand processes underlying habitat selection in tropical forest birds. We used multistate, capture–recapture models to investigate how the experimental removal of epiphytes affected monthly survival and movement probabilities of two resident bird species (Common Bush-Tanager Chlorospingus ophthalmicus and Golden-crowned Warbler Basileuterus culicivorus) in a Mexican shade coffee plantation. We found that bush-tanagers were at least 5 times more likely to emigrate from plots where epiphytes were removed compared to control plots. Habitat-specific movement patterns were not detected in the warbler. However, unlike the warbler, bush-tanagers depend upon epiphytes for nest sites and (seasonally) for foraging. Survival rates did not vary with habitat in either species. Interestingly, in both species, survival was higher in the non-breeding season, when birds are in mixed-species flocks. Movement by bush-tanagers into areas with epiphytes occurred mostly during the breeding season, when mortality-driven opportunity was greatest.