OTTAWA — The spring of 2012 was the earliest on record, shattering heat records across Eastern North America. But many common songbirds didn’t migrate early to take advantage.
Locked into a schedule that doesn’t change, they missed the best breeding time, raising questions about whether they will adapt to a warming world.
“What’s new is that Mother Nature did a fabulous experiment, giving us a window into how birds might or might not respond to dramatic shifts in weather patterns,” said biologist Bridget Stutchbury at York University.
“It’s the sort of experiment that you can’t conduct by yourself, or plan ahead of time.”
Purple martins migrate to Brazil and back. Stutchbury’s group tied tiny “geolocators” tracking individual bird’s movements during migration.
Spring of 2012 was “ridiculously warm,” she said. Ottawa, for instance, had a string of days with highs in the upper 20s in March.
Leaves came out early and insects hatched early, creating the perfect breeding environment for songbirds.
But the birds didn’t come. Instead they waited for the normal departure time from Brazil, arriving after their food supply of insects had passed its peak.
“They spend a month just non-stop feeding their kids, and the number of kids they produce is directly limited by how much food there is,” Stutchbury said.
As the northern hemisphere has a series of early springs, “there’s a mismatch between when the birds breed and when the food is available, and so there’s a real cost in not getting back (to Ontario) early.”
And she and co-author Kevin Fraser feel that some martins are genetically more early birds than others, passing down their preference for slightly early or late migration through generations. If so, it could take many decades for the bird population to adapt, as the early birds gradually produce more offspring in a series of warmer springs, and the genetic pattern of the martin population shifts.
But if the birds can learn to adapt, the pattern might change in just a few years.
Purple martins are in the swallow family.
Northern populations of martins and other insect-eaters are declining whereas the same species are doing fine in Texas and Arkansas, she said.
She says the new research provides evidence that an inability to adapt to early springtime in the north is one reason.
There has been one other quirk of nature to study since last year’s warm spring. Huge numbers of cicadas have emerged in the eastern United States this spring, an event that comes once every 17 years.
“They’re seeing the fattest purple martins ever,” Stutchbury said. “It’s like eating at McDonald’s all day every day.”