Diversified Farms Can Support Forest-Dependent Bird Populations

Forests appear to provide better habitat for forest-dwelling wildlife than farms. Despite this, Stanford researchers discovered in one of the world’s longest-running studies of tropical wildlife populations that, over 18 years, smaller farms with widely different crop types interspersed with patches or ribbons of forest preserve many forest-dependent bird populations in Costa Rica, even as forest populations decline.

Nicholas Hendershot and co-workers compared trends in particular bird populations across three landscape types in Costa Rica: forests, diversified farms, and intensive agriculture in a paper published on September 4^th, 2023, in the Proceedings of the National Academy of Sciences.

The sharpest declines were observed in forests, followed by intensive agriculture (and the species succeeding in intensive agriculture were often invasive). However, on diversified farms, a substantial subset of forest bird species, including some of conservation concern, increased over time.

Birds are kind of a proxy we use to track the health of ecosystems. And the birds we’re seeing today aren’t the same as we saw 18 to 20 years ago. This paper really documents this pattern.”

Nicholas Hendershot, Stanford University

Nicholas Hendershot was a postdoctoral fellow at the time of this research in Stanford’s Department of Biology in the School of Humanities and Sciences (H&S), the Stanford Center for Conservation Biology (CCB), and the Stanford-based Natural Capital Project (NatCap).

Food Security at Stake

The findings suggest that diversifying farming practices may be important for biodiversity, but biodiversity and food security are also linked. This entails having a variety of bird species that consume insects and aid in crop pollination.

“Identity does seem to matter a lot for pest control and other ecosystem services birds provide. These species are not interchangeable,” noted Hendershot.

We need a constant stream of pollinators servicing farms. About three-quarters of the world’s crops require pollinators to some extent, and that 75% is our most nutritious food—think of all the vitamins and minerals packed into fruits, nuts, and veggies.”

Gretchen Daily, Faculty Director, NatCap and CCB

Gretchen Daily is also the Bing Professor of Environmental Science in H&S and a senior author on the paper.

Gretchen Daily adds, “We need a constant stream of birds, bats, and other wildlife to help control pests: they suppress the vast majority naturally. And we need to start building flood protection, water purification, carbon storage, and many other vital benefits back into agricultural landscapes, way beyond what can be achieved in protected areas alone.”

Daily also pointed out that diversified farms do not always produce less food than intensive agriculture. “This is a recent assumption that is being overturned,” she adds.

Beyond Protected Areas

Protected areas are still essential, but they are too few and far between to provide the ecosystem services that both people and nature require to survive, it has become increasingly clear throughout the world. Working landscapes are essential for maintaining biodiversity and its advantages.

“People, including scientists, had the idea that farmland would not support a meaningful amount of biodiversity,” says Daily. Diversified farms not only provide habitat in this case, but they also connect otherwise fragmented forested areas.

I have moved away from the ‘fortress conservation’ model, which focused more on creating protected areas separate from human activities, and see more and more how much potential there is outside of forests. The forests are key – we need them, of course. But in addition to that, I’m always surprised by how important how you manage a farm is for biodiversity.”

Gretchen Daily, Faculty Director, NatCap and CCB

“We believe the findings of our research are new to science, but in a sense, it merely confirms what Indigenous communities around the world have already known for a long time, which is that humans can and should have reciprocal relationships with the rest of the local ecological community they are part of,” adds Tadashi Fukami, a Professor of Biology in H&S and of Earth system science in the Stanford Doerr School of Sustainability and a co-author of the paper.

Incentivizing Farmers

Costa Rica experienced the fastest rate of deforestation on a country scale in the 1980s and 1990s. Then they turned it around, becoming a well-known success model. Costa Rica reversed this trend by establishing the world’s first countrywide payment for ecosystem services (PES) program: forests now cover nearly 60% of the country’s land, up from 40% in 1987.

In the coming years, the country hopes to double the amount of protected forest. Any landowner can accept funds for reforesting even small portions of their land through the existing PES program. The government is also developing a new PES program to encourage farmers to use best management practices.

This research will assist Costa Rican policymakers in perceiving the long-term benefits of various farming practices. Daily added, “We need to recognize the vital work many farmers are doing that supports biodiversity.”