Chickadees are cavity nesters. Lacking the larger, stronger bills of woodpeckers, they either use a pre-existing cavity or excavate in material soft enough for them to remove. This is a foam archery target in the shape of a deer. My grandchildren use it for archery practice. It once had antlers. In one of holes that once held an antler, a pair of chickadees have made a nest. Their excavation is so deep that the nest cannot be seen. The birds picked foam from the hole for several days, and now presumably are incubating eggs. The foam is a perfect cavity material for them: it's soft, it holds its shape well, and its insulation qualities can't be beat. Chickadees are opportunists. Target practice, by the way, obviously has been put on hold.
