CHICAGO (CBS) — Our warmer-than-usual winter appears to have sparked a little early migration to the Chicago area for a couple of kinds of birds.

Field Museum collections manager emeritus Dave Willard has been monitoring bird arrivals to the Chicago area for more than 35 years, and he’s noticed the American Woodcock arrived weeks earlier than usual this year.

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“These were some of the earliest arrivals for big numbers of woodcocks,” he said.

Willard also said he’s seen a Ruby-crowned Kinglet earlier than usual.

Chicago Bird Collision Monitors director Annette Prince said the short, stubby, long-beaked woodcocks started arriving in Chicago at the end of February.

“Woodcocks are a bird that burrow in the ground for worms and other invertebrates; and there hasn’t been hard freeze, and the ground has been soft, so they’ve probably been edging their way north,” she said.

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Other birds start their migrations when daylight starts getting longer. That’s their cue to head north.

“Birds are a lot like an army. It travels on its stomach. So they move whenever there’s food,” Prince said.

According to Prince, Woodcocks must have kept coming north as they found thawed ground, which is what they need to burrow for worms and bugs to eat.

Willard said, while it’s “dangerous” to say climate change is *causing* early migrations, he does see a correlation.

“Analysis of data of bird reports has shown that a fair number of birds are arriving, on average, earlier than they did historically,” he said.

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Since many birds require insects to emerge for them to begin heading north again, it would seem a warmer climate might contribute to earlier migration.