Scientists with the U.S. Geological Survey say that while spring is arriving earlier in many parts of North America, it is not advancing uniformly for the migration routes of many birds.
The study by Eric Waller at the USGS in California was published in mid-September in the open access journal PLOS ONE, and reported also in EurekAlert, an online journal of the American Association for the Advancement of Science.
While climate change has been linked to earlier springs, not all species respond equally, and that threatens to put many species out of sync with their habitats, the study said. To understand how mismatches could impact migratory birds, researchers compared published data on the first appearance of leaves and flowers on deciduous trees for 496 federal wildlife refuges and four major North American bird migratory routes between 1901 and 2012.
Researchers found that spring is now arriving early in 76 percent of wildlife refuges in the U.S. and extremely early in 49 percent of refuges, compared to the early 20th century. For three of four migration flyways, spring advanced more rapidly at higher latitudes than lower latitudes, but there was no latitudinal pattern across the Pacific flyway, which covers the west coast of North America from Baja California to Alaska.
Mismatches in the timing of events across these migratory routes could mean the birds struggle to stay in sync with food availability and other seasonal changes, researchers said. Taking these differences into account when planning conservation strategies and defining refuges could help protect vulnerable migratory birds from extinction due to climate change, they said.