Research: Borer-eating warblers may need nearby forests

by on October 11, 2011

ResearchBlogging.orgRoosting behaviour of a migratory songbird on Jamaican coffee farms: landscape composition may affect delivery of an ecosystem service. Jirinec, Campos, and Johnson 2011. Bird Conservation International.

This is another paper from Matt Johnson and his students from Humboldt State University (CA) who study how birds provide pest control on coffee farms in Jamaica.  Previous papers summarized here include the primary research on which species of North American-breeding birds prey on coffee berry borers on Jamaican farms, and an analysis of how birds controlled the borers on shade and sun farms, and the economic value of the pest reduction.

This study looked at the most important bird species preying on the borers, the Black-throated Blue Warbler. This species was profiled here as part of our Know Your Coffee Birds series.

Researchers captured warblers on two farms in cultivated coffee patches. The birds were fitted with tiny radio transmitters, and the movements of 21 warblers were followed for 7 to 10 days with radio telemetry.

While the birds spend most of their days in the coffee cultivation areas, most (81%) birds roosted (spent the night) in nearby forested habitat patches, not on the coffee farms. Even if a bird roosted within the boundaries of the farm, it was usually in large shade trees or vegetated non-cultivated areas. The average distance between the daytime range and the roost sites was 119 m.

The structure of the vegetation on the farms where the birds foraged was quite different from where the warblers spent the night. Roosting sites had more canopy cover (averaging 94% closed) than the shaded coffee (36% closed). Roosting areas were also very dense. Thus, the Black-throated Blue Warblers in this study appear to choose coffee farms for their good food supply — which includes the coffee berry borer — and forests with dense protective cover to safely spend the night.

This implies that preserving forests, which provide safe haven for roosting birds, in or near coffee farms may encourage them to remain in an area. For farmers to benefit from the pest control services of migratory and resident birds, as well as other ecological services such as pollination provided by other fauna, local land use must be taken into account.

Male Black-throated Blue Warbler banded at the Rouge River Bird Observatory, photo by Julie Craves. All rights reserved.

JIRINEC, V., CAMPOS, B., & JOHNSON, M. (2011). Roosting behaviour of a migratory songbird on Jamaican coffee farms: landscape composition may affect delivery of an ecosystem service Bird Conservation International, 1-9 DOI: 10.1017/S0959270910000614

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Revised on February 8, 2013

Posted in Birds and other biodiversity,Research on coffee growing

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