Chickadees

About 60 species across the Northern Hemisphere, known as tits in Europe. Small, restless, cavity-nesting songbirds that stay put through the winter rather than migrating, and depend on food cached months earlier to do it. Their spatial memory is exceptional and the hippocampus enlarges seasonally to support it. They form the nucleus of mixed-species winter flocks, and their alarm calls are listened to by many other species.