You might have seen them in trees in your yard or neighborhood in Minnesota, but if it's not a hawk's nest, just what is that big ball of leaves?

While the leaves are starting to bud on trees across our fair state and are making them a little tougher to see, I've still noticed several of these big balls of leaves in trees in our neighborhood in the Land of 10,000 Lakes. Maybe you noticed them, too.

CSJ/TSM-Rochester, MN
CSJ/TSM-Rochester, MN

I always just thought they were the nest of one of Minnesota's many native birds, like robins, blue jays, or one of the species of sparrows. Or, more likely, I thought those big ball of leaves HAD to be the nest of a bigger bird of prey, like some type of hawk.

We have a family of red-tailed hawks who made a nest a couple of years ago high atop a tree in the woods near our house, and their nest does look similar to these balls of leaves.  But, it turns out that is incorrect. Well, it's half incorrect.

That's because while those big balls of leaves scattered in trees across the Gopher State are, in fact, nests, they are NOT made by birds. So just what are they? They're actually nests made by squirrels!

Curt St. John/Townsquare Media-Rochester, MN
A squirrel nest (drey) in a silver maple tree in southeast Minnesota earlier this spring. (Curt St. John/Townsquare Media-Rochester, MN)

Technically, these leafy nests are also called 'dreys.' And according to the Minnesota Landscape Arboretum, even though they're tougher to see with leaves now on trees across the state, they're fairly common in Minnesota in the fall, winter and even spring:

Dreys can be seen high in treetops. These are constructed of twigs and leaves, are spherical inside, and are typically lined with soft materials such as moss, shredded bark or pine needles. The entrance hole is usually located at the bottom of the drey facing the trunk to keep out rain.

The Minnesota Landscape Arboretum says squirrels native to Minnesota, like the red squirrel and the Eastern grey squirrel, are notorious drey-makers and tend to use those leafy homes for a year or two before abandoning them.

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And, unlike birds, who use nests only for incubating eggs and raising young chicks until the fledgling stage in the spring and summer, squirrels in Minnesota use their dreys for shelter and raising their young year-round.

However, this Mass Audobon story says that some species of squirrels, like the Eastern grey squirrel, do use dreys in the warmer months but prefer to spend the cold months in a more protected place, like a tree cavity.

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Gallery Credit: Dom DiFurio & Jacob Osborn