Why Do Animals Sometimes Kill Their Babies?

Is it natural—or pathological—when a mother kills and eats her own offspring? Or when a brother kills his sister's child?

When Khali, a sloth bear at the Smithsonian's National Zoo in Washington, D.C., went into labor in late December last year, her keepers were thrilled. But soon after Khali delivered her first cub, something went wrong.

"We don't really know what happened," says Tony Barthel, a mammal curator in the zoo's Asia Trail section. He and the bears' keepers were watching Khali on a closed-circuit television. They cheered when they saw the palm-size cub come into the world.

Then, 20 minutes later, Khali—still in labor with other cubs—bent down, not to lick her newborn, but to eat it. The cheers turned to gasps of dismay. "Our assumption is that the cub was not well, and it died," Barthel says.

Khali gave birth to two more cubs that day, and for the next week, she was as attentive, calm, and nurturing as a mother sloth bear could be. (She was an experienced mom, having raised two other cubs at a different zoo in 2004.)
The keepers continued to monitor her and her cubs, as they do with all bear mothers. So they were on hand when Khali ate another of her babies and turned her back on the third.

Rescuing a Baby ... From Mom
Barthel and the keepers decided they had to intervene. On January 6, they retrieved Khali's last surviving infant—a female—from her den. They rushed the cub to the zoo's veterinary hospital, where she was found to be hypothermic and suffering from an infection.

"She was ill, with an elevated white blood cell count," Barthel says. "We don't know if this was the case with her other two cubs, but my assumption is they were not well."

Shortly afterward, all the sloth bears fell ill with a flu virus, which may have caused the cubs' illness.To save the lone cub, the veterinarians immediately treated her with antibiotics and placed her in an incubator to restore her body temperature. A few hours later she was happily nursing from a bottle.

And the keepers were left trying to answer what seems the cruelest and most unthinkable of questions: Why would a mother eat her own young?

Babies as Food
"It can seem unnatural," Barthel says, "but there are reasons. They might sound cold to us, but they're simple—and they have to do with resources."

The sloth bear cub is bottle-fed at the zoo in Washington. [Photograph By Mindy Babitz, The Smithsonian's National Zoo]

Indeed, mother bears, felines, canids, primates, and many species of rodents—from rats to prairie dogs—have all been seen killing and eating their young. Insects, fish, amphibians, reptiles, and birds also have been implicated in killing, and sometimes devouring, the young of their own kind.

When mammalian mothers give birth, they must begin nursing their infants—something they can do only if they're healthy and well nourished. But if, for instance, a mother bear in the wild gives birth to unhealthy or deformed cubs, or is unable to find enough to eat, she will typically kill and consume them.
"They become a resource, one she can't afford to waste," Barthel says.

A mother bear—or lion or wild dog—does the same if she can't nurse her cubs or find food for them. And if one of her cubs dies, she'll most likely eat it immediately, as Khali did. This nourishes her and has the added benefit of removing the carcass. "That way there's nothing rotting in her den which might attract predators," Barthel says.

As reasonable as these decisions sound, there's still something profoundly upsetting about the deed—so much so that even biologists used to regard it as a pathological behavior. In some cases, depending on the circumstances, they still do.

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