A bird seeing a human face or hearing a human voice while under the staff's care could 'imprint' on humans, losing its natural fear and dramatically decreasing its odds of surviving in the wild. So when teaching the cranes to follow the ultralights, when they are around 5-7 days old, aviculturalists disguise themselves in a white smock and hood with goggles while wearing a hand puppet that looks like the head and neck of an adult crane and introduces each chick to an ultralight aircraft. The aviculturalists also bring a recorder with recorded crane brood calls to reassure the youngster. Only people wearing these costumes are allowed to get near the birds, even while flying with the flock.