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Why some animals eat their young

BY Rebecca Jacobson  April 9, 2014 at 5:10 PM EDT
These cheetah cubs at the Smithsonian Conservation Biology Institute in Front Royal, Va. may become foster siblings for a set of cubs that were injured, and nearly killed, by their mother. Photo by Victoria Fleischer/PBS NewsHour.

These cheetah cubs at the Smithsonian Conservation Biology Institute in Front Royal, Va. may become foster siblings for a set of cubs that were injured, and nearly killed, by their mother. Photo by Victoria Fleischer/PBS NewsHour.

Stacey Tabellario and Mindy Babitz are like many new mothers. They are with the baby every second she’s awake. They watch her on a monitor while she sleeps. They prepare bottles, talk to her and carry her and get little sleep themselves.

But the baby is a sloth bear (think Baloo from “The Jungle Book”), the only one of its kind born in captivity in the United States this year. And she is in Tabellario and Babitz’s care for a reason that’s simple and hard to dispute: when she was born, her mother ate her siblings.

“Now we’re mom,” said Tabellario one of the six zookeepers caring for the cub. “It’s an amazing experience, and we’re learning a lot, but there is still that bittersweet tone to it, because we all know that the first choice for any animal is to be raised by their mother.”

At first, zookeepers were thrilled when Khali, named for the Hindu goddess of destruction from the bears’ native India, gave birth to three cubs, an unusually large litter for a sloth bear.

science-wednesdayBut the first was stillborn. She consumed that cub immediately. A week later, she ate the second and began neglecting the third.

Tabellario says Khali’s reaction was normal, even healthy for a mother bear.

“It sounds very shocking, but it’s not something that shocks us as keepers. That’s the natural history of carnivores.”

This two-month-old sloth bear cub at the Smithsonian National Zoo is being raised by zookeepers after her mother ate her siblings.

This two-month-old sloth bear cub at the Smithsonian National Zoo is being raised by zookeepers after her mother ate her siblings.

It sounds counterintuitive to evolution, but infanticide in the wild is well-documented, said Doug Mock, professor of biology at the University of Oklahoma and author of a book on the subject. Animal parents have limited resources to dedicate to their offspring, he said, and if the baby is sick or weak, carnivores have been known to consume babies or abandon them. Cannibalism gives the mother the calories she needs to raise her healthy babies or get pregnant again.

Sometimes it’s the mother or father that kills; sometimes it’s the siblings. Mock remembers watching a group of egret chicks peck their sibling to death, while their mother stood idly by, cleaning her feathers.That may have been the case for Khali, Tabellario said. A necropsy of her second cub revealed that the cub had a parasite in its intestines, which Khali may have sensed. When the keepers pulled the surviving cub from the den, she was ill too.

Sometimes it’s the mother or father that kills; sometimes it’s the siblings. Mock remembers watching a group of egret chicks peck their sibling to death, while their mother stood idly by, cleaning her feathers.

“It’s the most startling thing I’ve ever seen in the field,” he said. “I literally sat and watched and thought, ‘Any second, the parents will step in and stop this.’”

When asked him how he felt witnessing this behavior: “My soul died,” he said.

Mock has seen birds push their chicks from the nest, abandon them, even starve them. In the animal kingdom, he says, infanticide is not about pathology. It’s about ensuring that the strongest offspring survive.

“It’s one of the less pleasant aspects of nature, something humans don’t like to think about. You want to think of nature as warm, cuddly and fuzzy,” he said. “We assume that other species look at offspring the same way we look at offspring… To us it seems as if (infanticide) must be some sick kind of thing, but it isn’t necessarily.”

Infanticide can be accidental, too, said Susan Margulis, associate professor of biology at Canisius College.

“The thing that people don’t realize is that most young animals die. Most die when they’re in infancy. Animals mostly raise two babies to adulthood. It’s just more noticeable in zoos,” she said.

That’s because motherhood has a learning curve, she said, and it doesn’t come to all animals naturally the first time. She worked with primates in zoos, and found that new mothers must learn how to nurse their young, and how to properly care for them.

“I’ve seen primate mothers that were good enough, but not great. Sometimes good enough is okay,” she said. “That first breeding attempt is a learning experience. You almost have to assume it’s not going to go well. In evolution, that very well could have been the case for humans ancestors as well.” She added, “Even human mothers need to work out details of how to do this new job that they may not have any experience with.”

This two-month-old sloth bear cub at the Smithsonian National Zoo is being raised by zookeepers after her mother ate her siblings.

This two-month-old sloth bear cub at the Smithsonian National Zoo is being raised by zookeepers after her mother ate her siblings.

Zoos can’t always wait for mothers to figure it out. That was the case for Ally, a cheetah at the National Zoo. This winter she gave birth to a litter of four cubs. At first, keepers breathed a sigh of relief, said Copper Aitken-Palmer, chief veterinarian at the National Zoo. The new cheetah mom was nursing and grooming her cubs normally. But three weeks later, zookeepers noticed that Ally was carrying her cubs in and out of the den more than normal. The cubs became lethargic, but Ally continued to pace with them.

Adrienne Crosier, who manages the cheetah breeding program at the Smithsonian Conservation Biology Institute, says the keepers typically leave cubs with their mothers for as long as possible, but something was clearly wrong.

“She was carrying them because she was nervous and agitated, and we do see a lot of very nervous behavior in first-time cheetah moms,” she said. “It was kind of a difficult situation because every time we tried to treat them it made Ally more agitated, which then made her want to carry them more, which then exasperated the injuries.”

Ally had bitten down on the scruffs of their necks too roughly, causing deep wounds which had become infected, Aitken-Palmer said. She estimates the zoo had a few hours to save the cheetah cubs. On Christmas Day, keepers made the decision to take the cubs away from Ally.

Ally had bitten down on the scruffs of their necks too roughly, causing deep wounds which had become infected, Aitken-Palmer said. She estimates the zoo had a few hours to save the cheetah cubs.“She went from a nervous mom to inadvertently doing mortal damage to these cubs,” Aitken-Palmer said. “We pretty quickly figured out that these cubs weren’t going back to their mom. And they may not make it at all. They were septic with very low glucose, which is blood sugar. The female actually came in seizuring, her blood sugar was so low. Frankly, I’ve not turned around a lot of neonates that were in that condition.”

One of the cubs died. The other three underwent three major surgeries each and hundreds of stitches over the following weeks. The cubs weren’t weaned, so they still needed milk and multiple feedings every day.

Cheetah cubs were critically injured when their mother became nervous. They went through three major surgeries, hundreds of stitches, and nearly died from the infected wounds. Now the keepers hope that another cheetah at the zoo will adopt them.

Cheetah cubs were critically injured when their mother became nervous. They went through three major surgeries, hundreds of stitches, and nearly died from the infected wounds. Now the keepers hope that another cheetah at the zoo will adopt them.

When animal mothers neglect or try to kill their own young in captivity, hand-rearing is one option, Margulis said, one that zoos utilize less than they did 30 years ago. Though in some cases, animal parents are so notoriously neglectful or the species is so rare, hand-raising becomes the first option.

At the Lincoln Park Zoo in Chicago, the Micronesian kingfisher, a rare bird with fewer than 130 individuals left in the world, is an “always-hand-raise” chick, said Dave Bernier, general curator for the zoo. Kingfishers, like many birds, are notoriously neglectful parents, he said, and the species is so endangered that each chick is valuable. But overall, as scientists have learned more about how animals behave in the wild, zoos have tried to minimize the amount of contact they have with young animals, and if they can, return them to their social groups.

“We did more hand-raising of animals in the past. At the time, it was a lack of understanding of the needs of the animals, which has changed. The time that the infant spends with their species is critical,” he said. “You might be providing all the nutrients but having the animal live with their group is more important, all the time.”

For the sloth bear cub, they do their best to recreate the care she would get from her mother. Early on, zookeepers wore the newborn cub in slings across their chests, because sloth bear mothers carry their newborns to keep the baby warm.

These bears may have Baloo’s laid-back attitude, but they are still dangerous, wild animals. The zoo stocks “emergency honey” in various locations around the facility. In the event of a bear escape, the emergency honey is thrown in one direction, while the keepers run in the other. Photo by Rebecca Jacobson

These bears may have Baloo’s laid-back attitude, but they are still dangerous, wild animals. The zoo stocks “emergency honey” in various locations around the facility. In the event of a bear escape, the emergency honey is thrown in one direction, while the keepers run in the other. Photo by Rebecca Jacobson

Feeding her was also a new challenge for the keepers. As a baby, she needed to be fed eight times a day. There are no sloth bear-specific formulas, so keepers mixed puppy formula and human formula for her bottles. The sloth bears’ refrigerator is stocked with mealworms, their favorite food, jams and fruits, which they started serving to the cub.

These bears may have Baloo’s laid-back attitude, but they are still dangerous, wild animals. She pointed to a jar of “emergency honey” on top of the refrigerator, which they save in the event of a bear escape. The emergency honey is thrown in one direction, while the keepers run in the other.

Now that the cub is two-and-a-half months old, she’s a toddler, and the keepers let her climb on them the way she would with her mother. Raising the cub is a new experience for all the keepers, so they’re constantly trying new methods for interacting with her, Tabellario said.

“We’re kind of just putting pieces together from other zoos, from books we’ve read about behavior, from what we know about natural history,” she said. “There is not a lot of information out there, so a lot of it is us learning as we are going, but so far we are on a good path. So far she’s a very confident bear. We have high hopes for her.”

The challenge, Tabellario said, will be reintroducing her to other sloth bears and teaching her to socialize with her own species — the sooner the better. That’s because hand-raised animals have a harder time mothering their own babies, Margulis said. Margulis has published studies on mice showing that pups that were raised in the same cages as their mothers were more successful mothers than mice raised alone. And in the primates she worked with, some hand-raised gorillas had to be taught to nurse and care for a baby.

“You can get into that vicious cycle. You have an adult that hasn’t been raised by mother, that hasn’t had experience with siblings or littermates, and they often aren’t good mothers as a result,” Margulis explained.

Bernier disagrees. Maternal care in animals is so varied, even among individuals in a zoo collection, that there isn’t enough evidence to say that hand-raising has a negative effect, he said.

“I’ve seen the same species where the females all treat their young differently. Some are very protective; some are lackadaisical,” Bernier said. “Their personality is very wide-ranging, and what they’re willing to tolerate is myriad. I think it’s a pretty natural process, and we let them go through the normal steps until they reject offspring.”

There the cheetahs have an advantage, Crosier said, because adoption is an option. It hasn’t been tried often in zoos, she said, but cheetahs in the wild occasionally adopt cubs whose mothers have been killed. She’s hopeful that Mitty, a cheetah at the zoo with six cubs of her own, will foster Ally’s litter.

“We are very hopeful that one of our females that is currently raising six of her own cubs will at some level accept these other three cubs,” Crosier said. “Every cheetah cub that is born in this population is critical for the future of the population. And we are at a point with our cheetah population in North America where if we don’t start producing a certain number of animals every year, we are going to not have cheetahs in the next 50 years in North America.”