Birds of a feather flock together. So why do animal moms sometimes adopt newborn or young critters of other species?

Adorable pictures of a dog nursing kittens, a cat nursing bunnies and even a tiger mothering piglets circulate widely on the Internet and often make local or national news. It’s even been claimed that a female pit bull raised three orphan turkeys.

We don’t know why a usually predatory species would care for a foreign youngster. Perhaps maternal instincts trump predatory ones. Or maybe there is a generational benefit for the confused parent. For example, kittens raised with rats grow into adults that do not attack rodents of the same species.

Although we may never know why cross-species adoptions happen, it seems clear that parental instincts and social interaction are among the most powerful forces in the animal kingdom.