Conserving Tropical Forest Birds: Even A Little Help is Beneficial

tags: conservation, rainforest, Costa Rica, birds

We all know the common wisdom; coffee grown on open plantations in Costa Rica is bad for the native tropical forest birds' long-term survival. But a new study shows that this situation is more complex than originally thought. According to this study, by Cagan Sekercioglu, senior scientist at the Stanford University Center for Conservation Biology, the presence of remnant forest fragments or individual native trees on the plantations can help some forest bird species.

"Even modest restoration efforts can increase their land cover and help some forest birds more than you would think," said Sekercioglu, who was lead author of the study.

Previously, nearly 200 bird species had been identified in coffee plantations either by capturing or observing them there.

"If you do that, you might think, 'Well, these birds are doing fine in coffee plantations," Sekercioglu said. But this alone was not conclusive evidence that the birds actually liked being on the plantations since they could have been merely passing through to another destination.

To test this hypothesis, Sekercioglu decided to follow individual birds more closely. The study was conducted in Costa Rica at the Las Cruces Biological Station of the Organization for Tropical Studies, where most of the forested terrain has been converted to open coffee plantations or pasture -- unfavorable habitats for birds. Sekercioglu assembled a team and set up a bird-banding and radio-tracking system to monitor the birds' positions throughout the day.

Sekercioglu's team used mist nets in the coffee plantations to catch a large number of birds of three particular species. Each captured bird was marked with two colored leg bands and an aluminum ring with a unique identification number. Then, using false-eyelash glue, they attached a radio-transmitter to each bird. The radio-transmitters had a battery life of one-to-three months. During the study, the team tagged and tracked a total of 156 birds. Then each team member tracked between one and six birds every day, beginning at dawn.

"We start before the birds are awake and moving," Sekercioglu explained. "We leave the station at 4:30 a.m."

The researchers recorded every bird's information in a database, including its species, band number and the number of daily sightings. The team tried to record at least 50 to 100 sightings for each of the 156 birds during a period of at least 10 days, Sekercioglu said. The study lasted for two seasons, each of eight months' duration.

Based on their findings, the team concluded that many tropical forest birds avoid coffee plantations, even though they had been frequently observed there by researchers in previous studies.

"When you radio-track birds, you realize many go through coffee because they have to," Sekercioglu said. "Seeing them in coffee does not necessarily mean they like it there."

However, this finding is not surprising because the coffee plant is not native to Costa Rica, so local birds do not eat the fruit or do they live among the open plantations. In fact, caffeine evolved as a pesticide to keep pests away.

"Although we caught all these birds in coffee, most of them prefer remnant forest fragments, individual trees and trees along rivers, which are called riparian corridors."

To calculate their results, the team compared percentages of different land-cover types in the area to the birds' preferred locations. Their findings suggest that humans and birds may be able to successfully coexist if farmers leave small reserves of forest, riparian strips or single trees interspersed throughout agricultural land.

"Remnant trees -- individual trees -- only covered 1.4 percent of the landscape, but some of the birds spent 25 to 30 percent of their time in these few trees," Sekercioglu explained. Similarly, some birds spent up to half their time in riparian corridors, which cover only 4.6 percent of the area.

"These small patches of trees are critical for these native birds," Sekercioglu observed.

Sekercioglu's recommendations are being used to develop a Las Cruces project encouraging local people to plant native trees around their farms and villages, and Sekercioglu and his colleagues are planning a workshop at Las Cruces on restoration ecology.

Additionally, more research is planned. In addition to banding and tracking birds, the research team also monitored more than 300 nests, collected more than 10,000 feather samples to analyze the protein content in birds' diets and took nearly 2,000 blood samples for genetic analyses and to study avian malaria, Sekercioglu added.

"The more we learn, the more we realize we don't know," he said. "That's why you need a multi-pronged approach to look at birds' habits from every level."

The study was published in the April issue of Conservation Biology.

Sources

Persistence of Forest Birds in the Costa Rican Agricultural Countryside by Cagan H. Sekercioglu, Scott R. Loarie, Federico Oviedo Brenes, Paul R. Ehrlich, AND Gretchen C. Daily. Conservation Biology 21(2):482-494 (April 2007) [abstract and PDF]

Press release (quotes)