Blended Families

From an outside perspective, the rearing of African wild dog pups by a domestic dog at the Potawatomi Zoo might seem like a strange idea.  In reality, it's nothing too out of the ordinary.  There is a long history of blended families in zoos in which different species come together.  Most often, a domestic animal is used as a parental surrogate for an exotic newborn, such as this case.  

Back in the days when most zoo animals came directly from the wild, it was common practice for dealers to focus their efforts of collecting newborns.  They were easier to ship, more tractable, and more likely to adjust to life in a zoo or circus than adults of the species.  The downside, of course (besides the obvious ethical implications, including how they were often collected) was their incomplete development and need for more intensive care.  Mammals, in particular, were a challenge if they were not yet weaned.  Prior to the development of milk formulas, the only possible solution was to provide milk from another source, and since it wasn't like you could keep a bottle of milk in the fridge in the jungle, that milk usually had to be attached to another animal.  Goats, dogs, pigs, and other female, lactating animals were used to nurse baby animals.  I've even heard of cases of nursing human women being pressed into service.

For birds, milk wasn't an issue.  Instead, it became practice - and still is, in some facilities - for zoos to place eggs laid in their facilities by rare birds under chickens or ducks to incubate and rear.  Some zoos prefer this brood rearing to the use of artificial incubators, judging live birds to be more reliable and less failable.

Today we have technology and equipment such as incubators and milk replacer, but, as in the case of Potawatomi's pups, there is still a vital role for cross-fostering.  It provides socialization opportunities, for example, that the animals might lack in other rearing situations.  These dogs will stand a better chance of interacting with other painted dogs in the future if, at the very least, they grow up with the understanding that they are some sort of canid, not humans.  

Cross fostering is also used within members of the same species.  Sometimes a mother may have too many offspring, and staff can split that large litter up with a female which may have a very small litter.  It makes things more manageable for the one mom, whereas in the case of the second, she might not be willing to go through the biologically-expensive effort of raising a very small litter, so having a few more mouths to feed can be beneficial.  In the case of birds, you can move eggs from inexperienced or incompetent parents and put them under more seasoned ones to increase the chick's likelihood of success.  Then the chicks will grow up healthy without imprinting on humans, or on the wrong species of bird.

Reptiles, amphibians, fish, and invertebrates, of course, are considerate and come into the world fully competent, removing the need for any of these hassles.