Bad (and good) news for Costa Rican farmers

STANFORD (US) — Knocking down forests to make way for farms and pastures in Costa Rica can drive away the birds that play a crucial role in distributing seeds, controlling insects, and pollinating plants.

But data from 10 years of careful counting of birds in rural Costa Rica have led researchers to conclude that birds and farmers can co-exist, to everyone’s benefit, if some trees are left in the fields and pastures.

“The take-home message is that local-scale action by farmers can help,” says Daniel Karp, a graduate student at the Center for Conservation Biology at Stanford University.


“Taking small steps like leaving some trees interspersed around their fields and planting several crop species instead of just one can make a difference.”

The study was established ten years ago by biology professors Gretchen Daily and Paul Ehrlich to address a critical question: how to sustain vital life-support services in farmland.

“Nature reserves alone will never be sufficient to provide flood control, climate stability, pest control, pollination, and other benefits on the scale required,” Daily says. “Yet there is great scope for harmonizing conservation and food production–there are smart ways to achieve multiple, economically crucial benefits.”

The data for the study, published in the Proceedings of the National Academy of Sciences, came largely from an American bird expert who first went south to Costa Rica as a Peace Corps volunteer decades ago.

Walking the line

To collect his decade’s worth of data, ornithologist Jim Zook regularly walked the same transects along paths and roads in Costa Rica. For 30 minutes he would take careful notes of the birds he saw and the impressive number of birds he identified by sound. He did this six times a year: three times in the rainy season and three in the dry.

“It’s an amazingly comprehensive database, ” Karp says.

It includes, for example, the fruit-eating fiery-billed aracari, which might be found in areas of low-intensity agriculture, and the pale-billed woodpecker, seen snacking on insects in the forest.

Zook’s transects ran through four regions of the country, with diverse climates and land-use histories. All were originally forest, but had grown to include agriculture, including melon, rice, cattle, coffee, pineapple, and sugar cane.

Zook’s travels showed that seed-dispersing, insect-eating and pollinating birds persisted in more traditional, low-intensity farms, but declined dramatically on industrialized, intensified ones.

Further, in highly intensified areas, bird communities were less stable, showing pronounced yearly fluctuations in abundance and species numbers.

Even simple measures can help the birds’ numbers and diversity. Instead of fences around their fields, farmers can plant rows of trees, known as live fences, Karp says.

“That’s actually really good for birds.”

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