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Junco Winter Flock Behavior
Juncos are one of the most common winter visitors to bird feeders and fun to watch because of their interesting social behavior. They leave the northern portion of their breeding range during October and November and migrate in flocks to their wintering areas in lower Canada and throughout the United States.
Juncos tend to winter in the same area year after year, so chances are the birds that arrive at your feeder are the same birds that were there last winter. The first birds to arrive are older and more dominant. The younger ones arrive next. Males tend to winter farther north than females, so the proportion of males in a winter flock will be higher the farther north it is. (It is not always easy to determine age and sex reliably in the field. In general, the darkest birds are the males. In the Pink-sided and Gray-headed forms found in the West, the sexes look alike.)
The flock stays in an area of about ten to twelve acres. Not all of the birds are together all of the time so you may see varying numbers of juncos. However, they all stay in that fixed area.
The flock has a social hierarchy with a pecking order in which males dominate females and adults dominate younger birds. Watch the juncos at your feeder and you can see the social hierarchy at work. Dominant birds will face another bird and raise and fan their tails revealing the white outer tail feathers. They may also rush at and peck or chase subordinate birds. Sometimes two dominant birds may face one another, extend their necks, and repeatedly raise and lower their bills as if in a little “dance.” Rarely will this end in a fight.
At night, the flock will roost together in the same place, usually in some dense evergreen cover. It is fun to follow the flock at dusk and see where they roost. In the spring, at your feeder, the males will chase the females as part of early courtship behavior. Males will also begin singing their musical trills. By April the juncos will have migrated north to their breeding grounds. Look for the snowbirds to return next spring.