Deforestation is one of the largest contributors to the climate crisis, and now there is evidence that its significant impact on our ecosystem is also affecting the diets of tropical birds. In a study led by the University of Utah, scientists used a unique method to determine the effects that replacing forests with coffee plantations have had on the foraging habits of these animals.

Seth Newsome
Professor Seth Newsome

Co-director of the UNM Center for Stable Isotopes (CSI) and Professor of Biology, Seth Newsome, is a co-author of the study which includes collaborators from across the globe. Published in Frontiers in Ecology and Evolution, Using stable isotopes to measure the dietary responses of Costa Rican forest birds to agricultural countryside” has already garnered national attention for its findings.

While the utilization of feather isotopic analysis to has been used to study the diet preferences of birds before, it has never before been integrated with radio telemetry to study the impacts of agriculture on birds that reside in tropical ecosystems.

Through the use of radio telemetry, researchers were able to track the movements of 49 birds of four different species to analyze their habitat use. They also collected and analyzed 170 feathers for stable isotope analysis to characterize their diet. 

The species analyzed by the researchers were the orange-billed nightingale-thrush, silver-throated tanager, white-throated thrush and ochre-bellied flycatcher. All of them make their habitats in both the forest and the open countryside where their diets consist of both fruit and invertebrates. Invertebrates, including insects, are vital to their food source, as they provide key nutrients, especially during the breeding period when birds are raising chicks.

Deforestation has forced about a third of the world’s bird population to survive in human-dominated environments. In the study, researchers focused on the Las Cruces Biological Station in southern Costa Rica which has gone from fully forested to 50% coffee plantations, 20% cattle pastures, and 10% human-modified environments. Only 20% of the land is now forest.

The results found that for three of the four species studied, the conversion of forest to agriculture has resulted in decreased consumption of insects by birds that primarily reside in coffee plantations in comparison to those that use intact forest habitat. This reduction in food diversity may have negative consequences for the health and survival of these birds, particularly during the demanding breeding period.

To combat this, promoting shade-grown coffee plantations that provide more diverse and natural habitats for birds and the insects they rely on may help to mitigate the impact of agriculture on these species. Shade-grown coffee plantations provide a more natural and diverse habitat for birds, which can lead to increased food diversity and improved bird health.

These findings have significant ramifications for conservation efforts in Central America, where coffee plantations are a significant source of income for many farmers. By promoting shade-grown coffee plantations and encouraging farmers to adopt more bird-friendly practices, conservationists may be able to help protect the diverse and fragile ecosystems of the region while still supporting the livelihoods of local communities.