Molting is done in the warm seasons before the breeding season. It usually cost 25 to 40% of the energy. The new feather production requires a lots of proteins so they must eat to grow faster. That is why molting in the warm season is advantageous because the bird can eat more and molt faster. The American Redstart is a common bird in North America that is well study for its molting. The male has a bright red orange feathers that are for the breeding season. They molt right after they care for their young, however, the day to departure the area results if the male is able to molt into this bright color or not. If the male can leave the young early enough, then they succeed to molt in this color, but if they are late, the molting will not be complete. This results the late molting males to have a lower breeding rate than the ones that completed their molting.
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