Keep an eye out for changes in chickadee behavior in the coming weeks.
To prepare for winter, chickadees form flocks in the late fall. The flocks are formed around a dominant mating pair and contain other adults and juveniles. These flocks of 6-10 individuals provide protection and food security for the birds.
Try at home: Fill your bird feeder with chickadees favorites: sunflower seeds and suet. Observe the behavior of chickadees at your feeder and the size the flock. The first birds to arrive at the feeder are typically the dominant mating pair, followed by others in the flock. Listen to the winter calls of the chickadee: “chickadeedee chickadeedeedee” (call to regroup as a flock) and “tseet” (feeding call).
Source: Stokes Guide to Bird Behavior