The value of birds in controlling agricultural pests

A bananaquit, (Coereba flaveola), found more commonly in the study in the shade coffee system. Image credit, Dusty Roades.One of the key rationales behind conservation is that ecosystems provide valuable services to society and therefore merit protection.  Studies can play an important role in making this abstract idea concrete by quantifying what these values are.

In this regard, a new study in Jamaica does a great job in quantifying the value that birds provide to coffee farmers by controlling agricultural pests. Matthew Johnson and fellow researchers looked at the role of birds in reducing the abundance of the coffee berry borer Hypothenemus hampei, the most destructive pest for the crop causing up to $500 million in annual damages.

The study excluded birds from certain locations using netting and found that coffee berry borers were 40-58% more prevalent in these areas. Based on these figures, the researchers estimated the economic benefit from the service that birds provided in reducing coffee berry borers to be $310 per hectare for the season or 20% of the total crop value.

On the surface, these findings, published in the journal Animal Conservation, appear to be good news for avian conservation efforts. If birds are providing substantial financial benefits to farmers, it should create incentives for protecting forest habitat and transitioning to shade coffee systems that have been shown to increase avian diversity and abundance.

Unfortunately, the results of the study are not quite so simple. The researchers conducted their bird exclusion experiments in both shade and sun coffee systems. They found that in both systems birds had a strong effect in reducing pest populations. They speculate that the sun coffee system may have benefited from being adjacent to forested areas. Larger sun coffee farms without nearby forests may not see the same benefits from birds.

More research is needed to help us understand how local forests and shade coffee systems affect the ecosystem service that birds provide farmers. Nevertheless, the results from the study are encouraging. Based on their findings and evidence from past studies, the authors offer the following preliminary recommendations,

Bird abundance and diversity are clearly associated with shade vegetative complexity and a recent meta-analysis suggests that bird suppression of insect abundance is positively associated with both bird abundance and diversity. Farmers and farm policy-makers seeking to enhance bird abundance and diversity should retain or establish shade trees, non-coffee habitat within and adjacent to farms, arboreal epiphytes and nearby forest patches.

--Reviewed by Rob Goldstein

Johnson, M., Kellermann, J., & Stercho, A. (2009). Pest reduction services by birds in shade and sun coffee in Jamaica Animal Conservation DOI: 10.1111/j.1469-1795.2009.00310.x