Climate change threatening some migratory birds that breed in Canada

Imagine a day when the familiar bird calls of spring are no more. This could become a reality in the face of climate change, new research suggests.

Researchers from the Department of Ocean Sciences at Memorial University of Newfoundland, as well Florida's Museum of Natural History, used satellite data as well as observational data collected by citizen scientists — bird watchers who keep an accurate account on the arrival and movements of birds.

They studied the interval between spring plant growth and the arrival of 48 North American bird species from 2001 to 2012.

What they found is that the gap grew by a rate of one day per year on average, or five days per decade.

• Welcoming an early spring? Chill out — it's not necessarily a good thing
• Tiny birds with tiny backpacks could help save Manitoba warbler species
• A third of birds in North America threatened with extinction

Most birds have been able to adapt to this change. But those who don't may miss a critical window to find good nesting spots and to feed on early-spring insects. 

For some species, this rate of mismatch was double or triple the average, meaning some birds are arriving as many as 15 days after spring starts. Nine species in particular are struggling to keep up, including great-crested flycatchers, indigo buntings, northern parulas, blue-winged warblers and Townsend's warblers.

All of these birds make their way to parts of Canada to breed.

"It's like Silent Spring, but with a more elusive culprit," Canadian Stephen Mayor, a postdoctoral researcher with the Florida Museum of Natural History at the University of Florida and first author of the study published in Scientific Reports said in statement.

"We're seeing spring-like conditions well before birds arrive. The growing mismatch means fewer birds are likely to survive, reproduce and return the following year. These are birds people are used to seeing and hearing in their backyards… To imagine a future where they're much less common would be a real loss."

As a result of a changing climate, biological spring — the time when trees begin to green and the local ecosystem responds — is arriving earlier across much of the eastern United States into Canada, studies have shown.

Most recently, the United States National Phenology Network — which tracks seasonal and natural changes — reported that many trees are blooming far earlier than the historical average.

Adaptation key to survival

Birds take their cues to begin their migration from the sun. As the sun rises earlier, this signals to them that they can begin their northward migration, feeding among mainly insects along the way.

But if there is earlier greening, those insects appear earlier and the birds may struggle to find enough food.

Will they go extinct? It could have happened in the past and we just don't know. We'll just have to wait and see- David Schnieder, Memorial University of Newfoundland

David Schneider, co-author of the paper and researcher from Memorial University of Newfoundland, said that now the key is to understand the effect it has on chick production. 

"The adult pair is really stressed to get enough food both for themselves and their chicks," Schneider told CBC News. "So if they are late, and the insects have passed then that's not good news for the chicks."

The birds who are able to adapt not only hold an advantage for feeding, but also for nesting.

Purple martins, for example nest in cavities, such as holes in trees. But if birds who are able to adapt to earlier greening arrive before them, they take up the good real estate, leaving the martins to find potentially less protected places for their nests.

"Even a small number of days can make a difference," said Kevin Fraser, assistant professor at the Avian Behaviour and Conservation Lab at the University of Manitoba in an interview with CBC News. 

East vs. West

Of the birds facing the most challenges, there is a clear difference in eastern versus western regions of the continent. That's because there are wetter conditions east of the Mississippi, which seem to play a role in hastening spring's arrival, said Schneider.

Fraser said that his migration studies show that long-distance migratory birds are facing challenges with the changing climate.

"What we're seeing with our individual birds, in a more advanced spring like we had in 2012…our birds weren't able to match that pace."

But the ongoing question for these researchers is, why are some birds able to adapt quicker than others? Schneider says this will be the next focus after this study.

The good news — if there can be any taken away from this — is that most birds only live, on average, five years, Schneider said, so they can potentially adapt faster than other animals that live longer. 

However, while birds have certainly adapted to a changing climate over the course of their existence, they've not faced this type of rapid change we're currently experiencing.

"Some will adapt. Some won't." Schneider said. "Will they go extinct? It could have happened in the past and we just don't know. We'll just have to wait and see."