As days shorten at summer’s end, photoreceptors in their brains trigger hormonal changes that stimulate many birds to molt into new feathers that will stand up to the rigors of a long flight. Their hormones also trigger a huge appetite, and they start eating voraciously, gaining significant amounts of weight.
Many insectivorous species supplement their diet with fruits, grains, and other items that can be converted to body fat, which birds burn efficiently for energy.
These hormonal shifts make birds increasingly restless, especially at nighttime.
Suddenly, one day it’s time to go!
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