Ecology and conservation of birds in coffee plantations of El Salvador, Central America.

摘要

Since the early 1990s, much interest in avian use of coffee plantations was inspired by hypotheses proposing that conversion of traditional coffee plantations, grown under a diverse canopy of shade trees, into modern, technified plantations with severely reduced shade canopies, contributed to declines of long-distance migratory birds. Published literature has not yet tested that hypothesis nor demonstrated a clear conservation benefit for birds of conservation concern (i.e., greater survivability, fitness, or productivity) in shaded coffee plantations compared with other available habitats. I field tested the hypothesis that coffee canopy characteristics influence migratory bird abundances in El Salvador. Migratory birds as a group were significantly more abundant in coffee plantations than in forest, but the pattern was not significant for individual species. Because conservation programs certify coffee plantations as ecologically sustainable and "bird-friendly" if they have ≥40% canopy cover, ≥12 native tree species ha-1, and many emergent trees, I regressed migratory bird abundance against these variables. Only 4 of 23 species analyzed were positively correlated to the variables. The results did not support the supposition that certification programs generally benefit migratory birds, or that coffee technification has harmed migratory bird populations. I also evaluated potential affects of existing certification criteria on 16 resident bird species that were potential beneficiaries of ecological certification, each being negatively associated with habitat disturbance. A coffee plot with 40% canopy cover and 12 tree species ha-1 would likely hold 12% of the disturbance-sensitive indicator species than natural forest plots. Overall, the existing certification criteria fell short in identifying coffee plantation characteristics associated with high richness of disturbance-sensitive bird species. Despite overall high bird species richness in shaded coffee plantations, their importance for birds of conservation concern is probably less than even small natural habitat fragments. Focus of coffee certification should be shifted from canopy characteristics to natural habitat patches. Farms that conserve natural habitat should be certified as biodiversity-friendly under three options: (1) small habitat reserves on-farm combined with diverse canopy cover in the production area; (2) medium habitat reserves on-farm; and (3) larger habitat reserves off-farm, as mitigation and through a biodiversity offsets program.