Weather Waves and Habitat Changes

This animation shows where the 21 species in the study occur during each week of the year. Brighter colors (yellows) indicate more species are present than darker areas (blues and purples); overall, the species spend more time in Central American wintering grounds than on their northern breeding grounds. Map and animation by Frank La Sorte.

Once again eBird data and the Cornell Lab of Ornithology studies highlight the importance of forest conservation for species survival, as seen in Climate Change Or Habitat Loss? Study Weighs Future Priorities For Conserving Forest Migrants:

Birds are among the first to let us know when the environment is out of whack. But predicting what might happen to bird populations is tricky. Studies often focus on a single issue or location: breeding grounds or wintering grounds, changes in climate, loss of habitat. But in the real world, nothing occurs in isolation. A new study just published in the journal Global Change Biology pulls the pieces together.

“This is really the first study to measure the combined impact of climate change and land-use change over a bird’s full annual cycle,” says lead author Frank La Sorte at the Cornell Lab of Ornithology. “Typically, studies tend to focus on the breeding season. If you do that, you’re missing the real story which is inherently dynamic and complex.”

The study merges projections for climate change with land-use change to model what the future might look like for 21 species of forest birds. Scientists ran dozens of scenarios to learn which combinations of factors would make this group of flycatchers, vireos, and warblers—all of which breed in eastern North America and winter in Central America—even more vulnerable to population decline.

Two key findings stand out:

  • Over the next few decades, already-declining populations of these study species may become even more vulnerable on their wintering grounds because of human-caused habitat loss.
  • By the end of this century, expected changes in rainfall and temperature may reduce available habitat and food on wintering grounds even further, threatening the birds’ ability to survive.

To reach these conclusions, study authors first set out to establish where the 21 species are currently found and in what density for every week of the year in every 4-square-mile block of land north of the Equator. They used observations that volunteers entered into the eBird database from 2004 through 2014. Then, they layered in modeled climate change projections (temperature and rainfall) from the 2013 Intergovernmental Panel on Climate Change and habitat data (land-use changes) from a variety of projects conducted by academic researchers, and the location of protected areas.

The authors found the 21 study species spend the majority of the year (approaching 60%) on their wintering grounds in Central America, where they occur in higher numbers and densities.

“Our findings indicate that land-use change on their wintering grounds in Central America may be the most pronounced threat for these birds over the next few decades,” says La Sorte. “That means more individuals of more species are likely to be exposed over a longer period of time to habitat loss as people continue to convert forests to cropland or grassland.”

“With this novel modeling approach, we can now put a number on how concentrated bird populations really are and hone in on areas such as northern Central America that are super-important for wintering migrants and where the threats they face are magnified,” says Cornell Lab conservation scientist Kenneth Rosenberg, a coauthor of the study. “This allows us to direct scarce conservation resources to where they are needed most.”

Find the entire article with photos of specific species here.

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