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Warmer winters in Missouri could change bird migration

Tree Swallows 2 RMBS 5-21-18.jpg
Bill Rowe
St. Louis Audubon
Two tree swallows sit on a street sign. Tree and barn swallows eat small insects like beetles and flies. When late winters are warm, some insects will come out sooner. One birder in the region spotted a barn swallow at Horseshoe Lake State Park in March.

Robins, tree and barn swallows, and other birds chirping in the morning is usually a welcoming first sign of spring in the St. Louis region. But bird-watchers are hearing birdsongs earlier than usual.

On Sunday, a birder in Illinois spotted a barn swallow at Horseshoe Lake State Park. Bill Rowe, president of St. Louis Audubon, said this is rather early for the region. “The general pattern is they start to come back in April from their wintering grounds in Central and South America,” he said.

Conservationists are concerned about what this could mean for the future of bird populations. North America has seen a net decline of close to 3 billion birds over the past 50 years due to habitat loss caused by urban development and drought, according to one study.

Jean Favara, vice president of conservation with the St. Louis Audubon Society, said early migrating birds could beat birds that migrate later in the spring to peak insect populations.

“It's often a problem with our birds that are doing long-distance migration such as warblers or orioles,” she said.

According to federal weather data, winters in Missouri now are about 4 degrees warmer on average than in 1970. This winter is between the 11th- or 12th-warmest ever recorded in the region and had the sixth-warmest February on record.

Some birds that fly back to the region in midspring along the Mississippi Flyway are shifting the timing of their migration with an early vegetation green-up and abundance of insects. When low temperatures maintain a consistent 37°F for a few weeks, insects and earthworms become more active.

This is ideal for insect-eating migratory birds that don’t rely on the length of the day to time their migration. On the other hand, birds like orioles, warblers and other long-distance migrators miss out on peak insect abundance, Favara said.

She added that insect population peaks are coming before some birds actually need them when they’re raising young. Scientists call this phenological mismatch.

“Young birds grow up so fast, they need that high protein content from insects to maintain their growth,” she said.

Along with this bird-to-bird competition, Bill Rowe said bird-watchers could miss out on seeing some less common gulls and raptors that migrate from their breeding grounds in the Arctic to Missouri during the winter.

Rough-legged Hawk RMBS 2-10-22.jpeg
Bill Rowe
Rough-legged hawks have breeding grounds in the Arctic. In the winter they migrate south to Missouri. Because of warmer winters, bird-watchers are less likely to see these raptors.

“The glaucous gull that hangs out along big rivers and the rough-legged hawk only come down south when it’s cold weather,” said Rowe. “If the winters are getting less cold overall, then there’s going to be fewer and fewer sightings of these birds.”

Britny Cordera is a poet and journalist based in St. Louis and is currently serving as a newsroom intern at St. Louis Public Radio.

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