CHICAGO — All those squirrel leaf nests you're seeing in Chicago trees right now are likely vacant.
Squirrels actually occupy the nests — called dreys — during the summer and fall and ditch them during the winter. It takes them weeks to construct the nests, which are made with leaves and have an interior lined with fur, feathers, rags and other leaves.
"Most should be abandoned by now, and if they're not, there will be squirrels stripping them out," said University of Illinois at Chicago distinguished professor of biology Joel Brown, who's also the founder of Project Squirrel — a citizen-based science project that allows individuals to track and observe squirrels in their backyards and elsewhere throughout the country.
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The nests, which can be larger than basketballs, provide perfect camouflage and shade for squirrels in the warmer months, Brown said. Leaf nests are inhabited by solitary squirrels unless a female is raising her young.
But in the winter, the squirrels flee their homes for ours, heading to attics and soffits. They also prefer tree hollows to the leaf nests in winter.
"In general most attics make a great winter home, but they abandon [human] homes in the summer," Brown said.
Squirrels can cause immense damage to people's homes, rolling up insolation into a nest or chewing through electrical cords, Brown said. But for the most part, they don't wreck their winter human quarters and will be gone by spring, he said.
Squirrels can build leaf nests anywhere, even inside cars, if they're not used often enough.
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