Conservation and ecology of birds in coffee agroecosystems of Chiapas, Mexico.

Abstract

Agricultural landscapes are receiving increased attention for their potential to contribute to biodiversity conservation. Shade-grown coffee certification is one market-based conservation program currently being used to promote conservation in tropical agricultural landscapes. This dissertation presents a useful approach for measuring the conservation potential for birds from coffee agroecosystems using natural conservation standards. Comparing bird census data from two forest reserves to a coffee intensification gradient of five coffee agroecosystems ranging from shade monoculture to rustic shade, this study finds that the diversity and abundance of forest-associated birds is reduced by increasing management intensity. However, the rustic management system that would qualify for shade-grown certification contained significantly higher levels of forest-associated birds than other non-certifiable management systems. Resident birds were more sensitive to coffee management intensity than migrant birds. Conservation benefits were also constrained by seasonal variation and extreme climatic events, in particular the summer breeding season and a drought following El Nino. Foraging behavior of birds is examined to assess the relative importance of structural and floristic diversity in contributing to avian diversity. The foraging relationships of birds are examined between management systems and across seasons to improve our understanding of the ecological role of birds within coffee agroecosystems. The vertical distribution of foraging bird species found in coffee agroecosystems resembles patterns reported for tropical forests. The vertical stratification patterns found by this study do not support the hypothesis that vegetative structure is the primary determinant of avian diversity within coffee agroecosystems. Other vegetative characteristics, in particular floristic diversity, also contribute to the conservation potential of these agroforests. This study also reports strong seasonal use of flowers and fruit. Insectivory varied significantly by season. This dissertation presents evidence that food resources associated with the greater diversity of plant species in less intensive coffee agroforests may facilitate coexistence for an increased number of bird species. Finally, this dissertation explores the ecology of an ectoparasite (Acarini, Trombiculidae) found on birds within this tropical landscape. This study reports a surprisingly high incidence and abundance of these chigger mites that varied seasonally on both resident and migratory birds found in coffee agroecosystems. Chigger mite incidence was greater during the winter dry season when long-distance migrants were present.