For months now, early every morning the songs and calls would
start – sometimes before dawn – and the raucous, beautiful and energetic bird sounds from birds like Carolina Wrens and this Northern Cardinal continued filling the soundscape until sundown. Then one day….suddenly the yard was oddly quiet. While some juvenile birds were still following their parents around and making food peeps, most of them had fledged and learned to fly well enough to keep up. Finally the parents could relax. After months of rigorous migration, mating and rearing chicks, it was time to disappear a little and not always be on guard. In fact, sometimes not only are adult birds not heard now, they are often not seen as easily. What happened?
After a busy breeding season, many birds are exhausted. Certainly the beautiful feathers they grew over the winter to attract a mate have outlived their usefulness and are likely worn out. To prepare for the migration south, or just to weather the winter where they are, they need to replace those feathers so they can efficiently fly and stay warm when the weather turns. So, they molt. And molting all their feathers can be a particularly risky proposition, for without full wings, they are not in perfect flight form, and therefore more vulnerable. Disappearing and being quiet is not a bad idea.
Want more info about molting and how different birds handle it? Check out this article from Cornell Lab of Ornithology.