Warming temperatures mean quicker migrations for birds in eastern North America, a UNC Chapel Hill biologist says in a newly-published paper.
A team led by Allen Hurlbert based its work on 48 million observations reported over the past decade by amateur birdwatchers to eBird, an online database. Results were published Wednesday in the science journal PLoS ONE.
The study focused on 18 species, all commonly found across the East. It analyzed when the birds arrived at various points on their migrations. On average, each species reached stopping points 0.8 days earlier for each degree Celsius of
increased spring temperature. But some species arrived up to three to six days early.
Timing is everything on birds' perilous journeys. Arrive too early, and no food may be available. Get there late and risk losing territory or mates.
Birds that migrate slowly, such as red-eyed vireos (right), are most likely to quicken their migratory pace as temperatures rise and slow them when readings fall, the study found. Those that typically make rapid or especially long migrations were more resistant to temperature cues -- potentially to their peril.
"They have to time it right so they can balance arriving on breeding grounds after there's no longer a risk of severe winter conditions," Hurlbert says. "If they get it wrong, they may die or may not produce as many young."
Hurlbert's coauthor was Zhongfei Liang, a former undergraduate student who helped analyze data.