Like all other blue birds, Indigo Buntings lack blue pigment. Their blue color comes instead from microscopic structures in the feathers that refract and reflect blue light, much like the airborne particles that cause the sky to look blue.
If you hold a blue feather up to the light, the dull brown-black color of the pigment melanin can be seen, not the blue.
A long-distance, nocturnal migrant, indigo buntings form large flocks and migrate south from their breeding grounds between September and mid-October, using the stars for navigation. The birds possess an internal clock that enables them to continually adjust their angle of orientation to a star—even as that star moves through the night sky.
Northward migration from its wintering grounds usually begins in late April or May. Females migrate up to two weeks later than males.