Fall migration is happening earlier for a North American bird species that is already in rapid decline, adding pressure to its chances for survival.
The trip south each year from Alberta to Central America has, over the last 32 years, moved ahead by an average of 14 days for a small grey bird called the least flycatcher, according to a new University of Alberta study.
The least flycatcher — so named because it's the tiniest of its group — has already seen a 53 per cent drop in its numbers over the last 50 years, from the effects of pesticide use and changing habitat. Because of this decline, it's designated as a priority species according to the Bird Conservation Region Strategy.
The shift, likely brought on by climate change, "could lead to an uncertain future for these birds," says study co-author Glen Hvenegaard, a professor of environmental science at Augustana Campus and co-author on the study.
"If climate change alters when and where the birds can get resources during their annual travels, it could add to a decrease in their population."
The least flycatcher is a valuable part of the ecosystem, eating insects and in turn serving as food for other animals including hawks, owls and squirrels.
Using data gathered by the Beaverhill Bird Observatory from banded birds over the last 32 years, the researchers analyzed the autumn migration patterns of the least flycatcher population in Alberta's Beaverhill Natural Area, one of the birds' breeding grounds.
The study is one of the few to focus on the autumn migration of the least flycatcher, giving insights not just into the behaviour of the adults, but also their newly hatched young.
"Autumn is when they get their first real survival test," Hvenegaard notes.
The findings showed that adult birds migrated 13 days ahead of young birds hatched that year, with adult females leaving five days earlier than their male counterparts.
The change could eventually mean the birds "fall out of sync" with the resources and conditions they need to breed, feed their young and survive, Hvenegaard says.
"The birds time their migration and nesting to match optimum temperatures and insect supply, for example. If they don't match, there would be poor conditions for the growth of the nestlings. Or, if the birds arrive back to their breeding grounds earlier in the spring, could a May snowstorm kill a lot of them?
"How long can these birds continue to exist, if that shift in migration goes on for another 32 years?"
As well, the hatch-year birds advanced their journeys south by about two days, raising similar concerns about their well-being, he adds.
"They're less familiar with places to stop to feed, they're less efficient, they're still learning, so it's possible they could be affected by conditions that are out of sync. That's concerning for a bird that only lives to five or six years old," Hvenegaard notes.
The findings from the study support the likelihood that climate change is influencing the migration shifts, he says.
"The triggers for migration are day length, temperatures and weather conditions, so when some of those are altered, it encourages the birds to fly south."
Efforts to reduce carbon emissions and protect boreal forest habitat are key to helping the least flycatcher live on, Hvenegaard says, adding that like all species, they are part of nature.
"They are survivors; they evolved from dinosaurs and have made it thus far. If we can learn from what is happening to these birds, we can change course before it starts affecting other species — including ours."
The study's co-authors include Myrthe Van Brempt and Geoff Holroyd of the Beaverhill Bird Observatory.
