Within the next few decades, human-caused habitat loss looms as the greatest threat to some North American breeding birds and the problem will be most severe on their wintering grounds, according to a new study published in the journal Global Change Biology. By the end of this century, the study’s authors say predicted changes in rainfall and temperature will compound the problem for birds that breed in eastern North America and winter in Central America. Migrant wintering grounds are important because the birds spend a greater proportion of the year in these places.
The scientists ran dozens of scenarios to predict what the future might look like for 21 species, most of them flycatchers, vireos, and warblers. They used observations that volunteers entered into the eBird database from 2004 through 2014 to establish where and in what density the species are found throughout the year. Then, they layered in modeled climate change projections (temperature and rainfall) and habitat data (land-use changes and the location of protected areas).
The study finds loss of wintering habitat in the near future will likely be magnified by the long-term effects of climate change. By the end of this century the study species are expected to encounter several significant changes:
- Greater warming on the northern breeding grounds and during autumn migrations — a surface temperature increase of about 9°F (5°C) with uncertain consequences for breeding and migration success; a smaller increase of about 5.4°F (3°C) is projected for their wintering grounds.
- Less rain on the nonbreeding grounds: a projected decline of 20 percent or more during the summer would reduce available habitat and food for birds arriving after fall migration.
- More rain on the breeding grounds, nearing 25 percent more during the winter on their breeding grounds. This could enhance vegetation growth and increase insect densities for returning spring migrants — a positive trend if the birds arrive at the right time.
“By examining the birds’ full life cycle, we learn that birds face a host of challenges all year long — and the intensity of those challenges shifts, depending on whether the birds are breeding, wintering, or migrating. Short-term conservation action will be most effective if it’s targeted to the times and places birds face their biggest threats. Knowing what may lie ahead in the long term underscores the need for action right now to offset the impact of climate change,” lead author Frank La Sorte said in an announcement of the publication sent to the press.
Photo: Rose-breasted Grosbeak, courtesy David Brezinski, USFWS.