Anne-Gabriela Schmalstieg and Corinna Esterer aren’t your typical foster mothers. For starters, the youngsters they care for aren’t humans—they’re captive-bred Northern Bald Ibises, a species that went extinct in Central Europe more than three centuries ago. For six months each year the two 20-somethings dedicate their lives to the birds, living onsite in campers at the Schönbrunn Zoo in Vienna, Austria, and looking after the ibises from sunrise to sunset seven days a week. The entire first month the women must abstain from coffee, alcohol, and cigarettes because they have to spit in the birds’ food to make it easier to digest. The chicks eat as many as 15 times a day, dining on a mash of rat, mouse, and chicken, as well as fresh grasshoppers. When the ibises aren’t eating or resting, the foster moms spend as much time as possible bonding with them. Cuddle time is key to ensuring such a strong connection that the birds will eventually follow the microlight aircraft...