As Summer Birds Reject Migration South, a Dangerous Trap Is Set

  • El Nino warmth helps strays survive, avoid winter's bite
  • Warmer temperatures delayed migration for some birds

This weather is for the birds.

Record warmth and no snow have turned the U.S. Northeast into a welcoming winter home for birds that would have normally taken to the skies weeks, if not months, ago for the trip south.

As long as the weather stays mild and the avian visitors find a food supply, they “could make it,” said Andrew Farnsworth, a researcher at Cornell University’s Ornithology Lab. “Any cold blast would create problems.”

Migrating birds seen on radar.
Migrating birds seen on radar.
Source: National Weather Service.

Birds that live in the north year-round cope with cold by puffing their feathers for insulation or finding shelter. Even those hardy creatures can die when temperature plunge. The visitors “that are lingering in warm conditions would likely starve if a hard freeze for more than just a night or two occurred,” Farnsworth said.

Among the species hanging around in the Northeast are various types of warblers, the rose-breasted grosbeak and red-headed woodpeckers. High temperatures reached into the high 50s and low 60s throughout the region this month.

Central Park had six December days with highs of 60 or more, and just one where the peak for the day fell into the 40s, National Weather Service data show Philadelphia has had two days in the 70s.

Record Warmth

November was the warmest on record across the world and every state in the contiguous U.S. was warmer than normal through the fall, according to the National Centers for Environmental Information in Asheville, North Carolina.

“This is typical of a strong El Nino, in that warmer Northeastern temperatures tend to associate with lingering and surviving neotropical migrants,” Farnsworth said.

Neotropical birds are those that breed in the U.S. and Canada during the spring and summer and then winter in warmer climes.

El Nino, a heating of the equatorial Pacific, pushes the northern U.S. toward a milder winter. In addition, other weather patterns such as the positive phase of the Arctic Oscillation are keeping cold air bottled up near the North Pole, where it can’t freeze the big cities on the East Coast.

Why Stay?

While the warm weather improves the birds’ ability to survive, Farnsworth said it may not be the reason they are staying.

“Presumably it’s a mix of birds that are misoriented and end up in the wrong places but survive because conditions are acceptable,” he said.

The cold of winter, which for meteorologists began Dec. 1 and for the rest of us starts next week, has yet to take a bite out of them.

If the temperatures do drop drastically, some species will be able to pick up and leave, Farnsworth said. There are birds that will always take advantage of good weather as long as they can.

While temperatures have cooled a bit this week, readings are forecast to climb again across the East and reach highs in the 60s in New York, Philadelphia and Washington by Christmas, according to MDA Weather Services in Gaithersburg, Maryland.

People taking part in the National Audubon Society’s 115-year-old Christmas Bird Count, the longest-running citizen-science bird project in the U.S., just might track down some unusual visitors.

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