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Birds breeding early to catch up to climate change

Courtesy of Powdermill Nature Reserve
Ruby-throated hummingbirds are breeding earlier and more quickly, but having fewer young than they had 50 years ago.


New research shows that in order for some early birds to catch the worm, they have to breed sooner in the spring.


Luke DeGroote is the avian research coordinator at Carnegie Museum of Natural History, and he runs the bird banding program at the museum's Powdermill Nature Reserve.


Right now, he’s in the thick of spring migration.


“It’s sort of a bit like fishing, in a way. We put out our nets to see what we catch,” he says.

From early in the morning, until about noon, he and a handful of volunteers patrol a series of nets that look like volleyball nets that are set up around the property.


“This is a red-winged blackbird. I’m going to grab him by the body, and very carefully pull the netting off the tip of the wing,” he says.


Birds like this little guy, with the distinctive red patch on its wing, get caught up in the fine netting, and drop down into a pocket where they’re scooped up by researchers.


Credit Kara Holsopple
Luke DeGroote

DeGroote gingerly places the bird into a bag, like a small pillow case, and loops its string to a red carabiner around his neck. Red indicates which size metal band to place on the blackbird’s leg, so it can be tracked.


All the birds they capture this morning, and every morning, are taken back to a small lab where they’re banded with a unique number and weighed. Researchers also examine their feathers to determine age, and if the birds are getting ready to breed.


“The females will lose the feathers on the breast and then insert some fluid to create really like a hot water bottle for the eggs,” says DeGroote.


Early birds


They’ve been collecting these data here at Powdermill, consistently, for over 50 years. That’s how they know, from previous studies, that birds are migrating here a little earlier in the spring than they used to, and breeding sooner.


And that got DeGroote and his research partner Molly McDermott thinking:


“All right, if they're migrating early and breeding early, are they breeding earlier because they're migrating early or are they breeding more quickly after they arrive?” says DeGroote.


Their findings?


“They're basically getting busier earlier after arrival,” he says.


That’s true for the majority of the 17 common bird species they studied. In their recent paper, published in the journal PLOS One, they connect early breeding to warmer springs and climate change.


Credit Courtesy of the Powdermill Nature Reserve
The hooded warbler is one species now having fewer chicks.

Because while birds are arriving here a day earlier for every one degree Celsius that the temperature has warmed over the last few decades, spring buds are opening three days earlier.


Those plants, and the insects birds rely on for food for the survival of their young, are now sort of mismatched with the timing of spring migration. So these birds are responding the only way they can.


“They're having to catch up because they're not able to catch up during migration; they're not able to sort of advance that as much as the plants. They have to begin breeding soon after arrival if they want to breed at a time period that's sort of what they're used to,” says DeGroote.


In other words, when the tender plants and insects they eat are at their peak. A quarter of the species which bred earlier in this study, like black-capped chickadees, had more babies in these warmer years. But another 25%, including hooded warblers, didn’t. Their productivity declined.


DeGroote says you can look at the results of this study two ways. On the glass-half-full side, it shows some bird species are flexible, and capable of adapting to climate change. But while weather isn’t climate, a few years ago there was a hard winter and later spring, and this year is warmer, he says the overall trend for birds is worrying.


“If it continues to warm, that window which they have to be adaptable is shrinking,” says DeGroote.


This most recent study just looks at the timing of bird breeding, but DeGroote says it’s easy to see implications for the ecosystem. If some species are less successful because of climate change, there might be fewer birds to pick off insects or spread seeds from the fruits they eat.

Kara Holsopple is with the environment news program, The Allegheny Front.

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