Winter has finally gripped us with its snow, ice and below-freezing temperatures. It hit us over the head after we experienced one of the balmiest Decembers on record.
On the heels of the mid-January storm — and even in the wake of it — thousands of sandhill cranes, trying to winter farther north in Wisconsin, responded by flying south over the Chicago region to where they can find open water and food.
The trumpeting calls filled the sky as they typically do in November and early December. On Saturday, just before the temperatures began dropping to single digits, flocks of cranes flew over Deerfield and Long Grove. The day before, thousands of migrating cranes were counted in the region. They were still coming on Monday.
Migratory birds like cranes experience a restlessness called zugunruhe, when it’s time to begin flying south or north. Changing amounts of daylight as well as inner cues like hormonal changes can unlock this restlessness. Why then would a crane that typically gets its innate cues to begin migration in November wait until January? The answer lies, in part, with food, and it’s also likely related to climate change.
Sandhill cranes feed on waste grains, especially in cornfields, and on snails, frogs, lizards and insects in wetlands. Sandhill cranes have little blood flow in their legs and feet, and are able to withstand cold temperatures. If food is plentiful, they may linger longer than normal, and they have been doing that for the past few decades.
Still, when snow begins to fall and the wetlands freeze over, they must fly to where there’s more food. Sandhill cranes are large birds capable of catching updrafts to glide rather than flap their wings constantly. They are also much stronger flyers than the small birds. That gives them an edge over other bird species such as the ovenbird, a regular migrant in Illinois, and the black-throated gray warbler, a very rare species in Illinois.
Both species, which weigh less than an ounce and measure about 5 or 6 inches long, have been seen in the Chicago region this January. The ovenbird should be in the southern United States or northern Venezuela right now, and the black-throated gray warbler should be in Mexico. Both are mostly insect-eaters.
In early January, the ovenbird found a warm spot in downtown Chicago where some insects remained. The black-throated gray warbler found a little haven of evergreens in a Chicago suburb next to a feeding station with peanut shavings and other foods it found palatable. It was still being seen on Jan. 14, after nearly a foot of snow fell in some places. Temperatures dropped to below zero after that.
In this cold and snow, the ovenbird and the black-throated gray warbler likely will not survive. They certainly cannot fly in this weather. They may have to rely on humans to keep them fed, and they may perish nonetheless.
One study showed that ovenbirds cannot survive when the temperature goes below a certain threshold, about 24 degrees for a sustained period. Different bird species likely have different thresholds of temperatures they can withstand. Even though they really are not supposed to be here this time of year, it’s sad to think of these two species perishing.
What’s also sad is wondering what happened to the more than 30 limpkins seen through Illinois for the past several months, including in Lake Forest and Glencoe. The limpkin lives in tropical areas, from southern Florida to the Caribbean islands, Mexico and Central and South America. It does not migrate, and eats snails in wetlands.
For various reasons related to food and habitat, it is expanding its range northward, and has found plenty of snails and mussels to eat in Chicago-area wetlands. Still, it does not have adaptabilities like other species that live year-round here in the north.
For example, the black-capped chickadee can maintain a body temperature of 100 degrees, even when temperatures are hovering around zero degrees, according to the U.S. Fish and Wildlife Service. Chickadees also grow more feathers to provide better insulation in winter and store their food, remembering on cold days exactly where they left it. Some scientists think that the part of their brain where memory is stored, gets larger in winter.
A limpkin has not evolved to grow extra insulation in winter. When water freezes over the snails it eats, the limpkin is left without food. No food and colder temperatures than it is used to surely will not help these individuals survive.
The last time the limpkin was seen in Lake Forest was Jan. 11. Then came the snow and the freezing temperatures. What happened to this limpkin, and the others hanging around in our region? Did they die? Did they fly back south, even though they have not evolved to migrate?
One limpkin that remained in Ohio into December died after its wetlands froze up and it could not get to its food. A sad photo shows the limpkin staring at a snail embedded in ice.
Though we’d like to think of birds as simple creatures that need food, a place to live and a place to raise young, they remain the canaries in the coal mine, telling us stories of how habitat loss, climate change and invasive species affects their survival.
Sheryl DeVore has worked as a full-time and freelance reporter, editor and photographer for the Chicago Tribune and its subsidiaries. She’s the author of several books on nature and the environment. Send story ideas and thoughts to sheryldevorewriter@gmail.com.
