Hornbills nest in hollow trees where the male seals the female in using mud and feces. She is dependent on her mate to feed her for 4 months until the chicks fledge. Females’ necks are black while males are yellow and have a “wrinkled” beak. More than 50 have hatched in the U.S. since 1988 while breeding at the Tulsa Zoo commenced in 2007.