I was recently asked where the indigo buntings had gone. For the most part, they’re still here. But in late summer they have molted, changing the brilliant blue of the males for insignificant drab. Almost all our birds have a complete molt in the fall, loosing and replacing both their body feathers and their flight feathers. The flight feathers are lost symmetrically; when the outer primary of the right wing is lost, the outer primary on the left wing is lost. Thus, flight is maintained. In waterfowl, however, all the flight feathers are molted at the same time, and they are flightless. That’s why you don’t see geese at Ivy Creek at this time of year. They have moved to larger bodies of water to be safe from predators doing molt. The energetic cost of molt is budgeted to occur before the energetic cost of fat deposition prior to migration. Barn swallows, that migrate during the day and can feed on insects during their flight, however, molt during migration. In the spring, the birds molt again. This time, usually only the body feathers are lost and replaced. Goldfinches are an exception in that they molt and replace all their feathers again prior to the breeding season. Perhaps they can afford to do this because they are permanent residents and need not suffer the huge energetic demand of migration.
