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Climate Change Cues Tree Swallows to Nest Too Early in the Spring

Animals
Climate Change Cues Tree Swallows to Nest Too Early in the Spring
The Forest Vixen's CC Photo Stream. Flickr / CC BY 2.0

Spring is coming. And soon, tree swallows will start building nests. But as the climate changes, the birds are nesting earlier in the spring.


"It's getting warmer overall. They're thinking, OK, it's a good time to breed, to lay my eggs," says Lily Twining of the Max Planck Institute for Animal Behavior in Germany.

She says that despite recent warming, late-season cold snaps remain common. Those cold snaps can harm newborn chicks.

Hatchlings cannot regulate their body temperature, so they are vulnerable to hypothermia. And the insects they eat stop flying in cold weather, potentially leaving the chicks to starve.

"These chicks are growing very, very fast," Twining says. "They have very high energy demands, so… if they don't get a lot of that good high-quality food during this pretty specific time… that's when these cold weather events seem to be most devastating."

For example, data from Ithaca, New York, shows that a single cold snap in 2016 killed more than 70% of baby tree swallows.

"And there have been more and more of these severe cold weather die-off events for these tree swallows as they've been breeding earlier and earlier over the past 40 or so years," Twining says.

So for these songbirds, earlier springs can come with devastating consequences.

Reposted with permission from Yale Climate Connections.

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