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The next time you sip a cup of Costa Rican coffee, take a moment to thank the yellow warbler. A , published in , shows this bird is one of five species that help protect Costa Rica’s coffee crop by eating the loathed berry borer beetle that has now invaded almost every major coffee producing country. Coffee is one of the world’s most important and economically profitable crops, currently grown and cultivated in more than 50 countries.

The study revealed that birds are capable of cutting borer beetle infestations by almost half. The effect was dramatically amplified the closer the coffee plantation was to the forest where the birds live, illustrating that trees filled with birds are a major asset to farmers, who can reap $75 to $300 more yield from coffee per hectare.

“[This is a] really exciting, win-win opportunity for [farmers] to simultaneously increase production of agriculture while also engaging in conservation efforts on the farm,” said lead study author, Daniel Karp.  

The Africa-originating berry borer beetle arrived in Costa Rica in 2000 and has already caused significant damage. The beetle gets its name because it bores itself into the coffee bean, then eats its way out. Farmers can lose as much as 75 percent of their crop because the bug is largely invulnerable to pesticides.

To find out if birds could help cut down on the infestation, Karp and his Stanford colleagues measured what happened to borer infestation rates when they prevented the birds from foraging on the coffee bushes. They covered the crops with bird-proof cages of fine mesh, and watched what happened to the infestation rate in both the rainy season and the dry season for the crop. During the beetle’s peak time—the wet season—the borer infestation rose from 4.6 percent to 8.5 percent when the birds were excluded.

Next, the researchers used mist nets to catch and identify the different types of birds helping the farmers.

“[We] put them in cloth bags, which were previously sterilized,” Karp explained, “By the time we finished processing the bird, they would have left us a fecal sample that we would then collect and analyze for DNA of the pest. By doing so, we identified five species that were consuming the berry bore.” The birds they identified were the yellow warbler, the buff-throated foliage-gleaner, the rufous-breasted wren, the rufous-capped warbler and the white-tailed emerald.

The scientists then calculated the abundance of the birds, the forest cover near the farms and the beetle populations. Beetles were more abundant in crops not surrounded by woodland. The birds were more abundant on land that contained patches of rainforest. They were less abundant when the forests—large forest preserves—were only on the outskirts of the plantation. In other words, the more birds there were, the fewer beetles and the higher the plantation’s profits.

Karp hopes to further his research on this win-win situation to possibly create a framework for pest management.

“The next step is to generalize these results to try to create some decision support tools for land managers so they could take a guess at how many benefits they could get under different land management scenarios,” he explained. In other words, he hopes to create a framework that will illustrate the financial benefits wildlife can provide farmers, and help encourage the preservation of these helpful birds’ habitats.

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By Barry Yeoman