How do birds replace their feathers?

Each year, migratory birds must engage in three energetically demanding activities: breeding, migrating, and molting. Molt is an important process that is not as glamorous (and hence not as widely researched) as breeding or migration. For most birds, each feather must be replaced at least once a year. Let's face it, feathers are quite crucial if you're a bird – it's difficult to migrate with bad feathers, and it's difficult to attract mates if your feathers are dirty and drab.

It's no surprise that most birds split these three expensive actions; normally, attempting to weight lift while running a marathon is a terrible idea. For most songbirds, this entails breeding, then returning to the breeding grounds for a few weeks to molt before travelling south, and sometimes freshening up with a few new feathers before returning north to breed. Feathers cannot grow any farther and may get worn, damaged, or faded over time due to regular wear and tear. Molting replaces these damaged feathers and also makes males more appealing to females, which is why many molts occur during the mating season.