In late April redbud trees are popping in the Laurel Highlands, and Luke DeGroote is in the thick of spring migration. DeGroote is the avian research coordinator at Carnegie Museum of Natural History, and runs the bird banding program at their Powdermill Nature Reserve in Westmoreland County.
Most mornings DeGroote and a handful of other volunteers tromp through spring puddles and scour a series of nets–kind of like volleyball nets–which are set up around the property.
“It’s a bit like fishing, in a way,” DeGroote says. “ We put out our nets to see what we catch.”
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Birds get caught up in the fine netting, and drop down into a pocket where they’re scooped up by the researchers. On the morning I visit, DeGroote is loosening the net from the feet of a red-winged blackbird, one of the larger birds they see here. The blackbird is pretty feisty, but when it’s finally freed, DeGroote gingerly places it into a bag that looks like a small pillow case. He loops its string to a red carabiner around his neck. The color red indicates which size metal band to place on the blackbird’s leg, so it can be tracked.
Featured Image: Ruby-throated Hummingbirds are breeding earlier and more quickly, but having fewer young than they had 50 years ago. Clockwise from top left: DeGroote carrying birds around his neck (Photo: Kara Holsopple); The Hooded Warbler, one species now having fewer chicks; DeGroote checking nets; DeGroote with a Northern Flicker. (All photos except where noted courtesy of Powdermill Nature Reserve)
All the birds they capture this and every morning are carried 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 like a hot water bottle for the eggs,” DeGroote says. It’s called a brood patch.
The team at Powdermill has been collecting these basic data consistently for over 50 years. That’s how they know that birds are migrating here a little earlier in the spring than they used to, and breeding sooner.
In his most recent paper, published in the journal Plos One with co-author Molly McDermott, DeGroote was looking to go a step further.
“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?” he asked.
The answer is that a majority of the 17 common bird species they studied were breeding more quickly after they arrived. DeGroote and McDermott connect this early breeding to warmer springs and climate change. Because while birds are arriving in Western Pennsylvania a day earlier for every 1-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 and for the survival of their young, are now sort of mismatched with the timing of spring migration. So 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,” Degroote says.
These birds have to begin breeding soon after they arrive if they want to breed at a time period when the plants and insects they eat are at their peak. On average, DeGroote says, the birds they looked at are breeding about two or three days earlier per decade.
A quarter of the species which bred earlier in this study–like the black-capped chickadee– were more productive, meaning they had had more young, in these warmer years. But another 25 percent, including hooded warblers, didn’t. They had fewer chicks.
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. On the flip side, weather isn’t the same as climate. A few years ago there was a hard winter, and later spring, and this year it’s warmer. But DeGroote sees a warning in the overall trend for birds.
“If it continues to warm, that window which they have to be adaptable is shrinking,” he says.
While this most recent study just looks at the timing of bird breeding, 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.
Next DeGroote hopes to look at how birds might be affected by another aspect of climate change: more frequent and intense weather events, like snowstorms.
“Who knows what other questions we might come up with,” DeGroote says. “You know 10, 20, 50 years down the road this data will still be collected in the same manner to be available for those sorts of studies.”