Josh Engel, a research assistant in the Bird Division at the museum, said some hardier songbirds may have tried to stick out the winter in Chicago to stay close to summer breeding grounds and may not make it through the subzero temperatures.
“Evolutionarily, birds have adapted to deal with cold, but this is pretty extreme,” Engel said. “Extreme weather definitely pushes birds around in weird ways.”
He said the population of yellow rump warblers, golden crown kinglets, brown creepers and other songbirds would be reduced if they were not able to find somewhere warm to weather the cold snap.
“I’ve heard lots of reports of birds turning up in strange places to stay warm, like inside people’s garages,” Engel said, adding that dead bird sightings have also been reported.
Engel said for birders willing to brave the cold, the severe temperatures could drive some species to the open water of Lake Michigan as smaller lakes freeze over. He said the chances are higher for spotting long-tailed ducks and other waterfowl that typically winter on smaller bodies of water.
He said spottings of species like red-breasted mergansers and golden eye ducks are more common as the birds take shelter from the wind in shallower waters. He said the birds that typically breed in northern Canada and migrate to the Atlantic Coast are increasingly routine in Chicago.
“A lot of them will stay as far north as they can,” Engel said. “I was at Monroe Harbor and there were a number of mergansers and golden eyes looking very cold.”
He said the last major bird count was on Christmas Day, and the extent of the effect of the cold snap on bird populations would likely not be clear until spring counts — and migrations — begin.