Shade Management and Foraging Resources of Forest Birds in Coffee Agroecosystems in Chiapas, Mexico

Abstract

Shade-grown coffee has received much attention for providing bird habitat in tropical regions. Within shade coffee production, canopy management can vary greatly, and this variation may produce changes in the availability of food resources for forest-associated birds. To evaluate food availability and habitat quality in two farms with different shade management styles, bird foraging behavior was analyzed in terms of prey attack rates and foraging substrates utilized. These behaviors were examined in two species, the Yellow-green Vireo (Vireo flavoviridis) and the White-winged Tanager (Spermagra leucoptera). Measurements of individual body condition, including fat reserves, mass, and blood hematocrit levels were compared to provide an additional index of habitat quality. Significant differences were encountered between farm types both in the variety of shade trees used as foraging substrates and the rate of prey attack, indicating a decreased availability of food resources for birds foraging in the low shade coffee farm. A confounding factor in comparing these farms is that in addition to differences in the amount of shade cover, there is a vast difference in the diversity of trees present. To control for this, foraging behaviors were also compared within common shade tree genera between farms, which led to similar results as those found in the aggregate data. These results suggest that the shade management style--both shade tree diversity and amount of shade cover--affects the availability of food for forest-associated birds, and this likely contributes to the high avian diversity observed in high shade coffee farms. ii