Habitat selection by an avian predator of insect pests on Jamaican coffee farms

Ecosystem services provided by mobile organisms can be influenced by the availability and vegetative complexity of the habitats those organisms select. On Jamaica's coffee farms, birds assist farmers by consuming the coffee berry borer (Hypothenemus hampei), and the Black-throated Blue Warbler (Setophaga caerulescens) is a foremost avian predator. Using radio telemetry, we investigated habitat selection of 47 Black-throated Blue Warblers on two coffee farms in Jamaica differing in vegetative complexity during two winter seasons (2008-2009 and 2009-2010). We modeled habitat selection using four variables describing coffee habitat: canopy cover, coffee cover, distance to non-cultivated habitat, and distance to nearest shade tree. Within their home ranges, birds used coffee farm and other habitats similarly at the complex farm but used the farm significantly less at the lower complexity farm. Within coffee farms, birds selected for home ranges with high coffee cover and high canopy cover, with stronger selection at the more complex farm. Within the portions of their home ranges on coffee farms, birds also selected for areas with high canopy cover. In contrast, bird use of the coffee layer itself decreased with increasing canopy cover, dropping from 100% to 30% use of the coffee layer from zero to full canopy cover. Our results suggest that while birds were more likely to use coffee farm habitat with increasing canopy cover, at very high canopy cover birds were less likely to use the coffee crop layer itself, where they could consume the coffee berry borer. In this system, farmers can likely maximize conservation biological control by maintaining high coffee shrub cover and moderate canopy cover. These results suggest an underappreciated reason why mobile organisms may fail to deliver conservation biological control: natural habitat becomes so attractive to pest predators that spillover use of crops is reduced.

Automated summary

Through a study on the home range utilization of 47 Black-throated Blue Warblers in two coffee farms in Jamaica, it was found that birds selected areas with high coffee shrub cover and high canopy cover. However, when the canopy cover of the coffee farm reached a certain high level, the use of the coffee layer itself decreased, reducing their ability to consume the coffee berry borer.