Why Big Cats Kill Their Cubs
Are they bad mothers for abandoning, injuring, or even killing their newborns?
Take Aurora, the popular female polar bear at the Toronto zoo, for example. She killed two of her cubs in October, and had a third one taken away by zoo staff for hand-rearing to prevent a similar fate. She did the same thing the year prior, killing two of her cubs at birth by partially eating them.
It is well known that males will attack or eat their young and others, but mothers failing to care for their young, and animal infanticide in general is a touchy, almost taboo subject for major zoos, including Toronto’s. After all it doesn’t exactly drive attendance.
Yet it’s a phenomenon staff deal with and one that can be traumatizing for zookeepers, say Toronto zoo officials.
“It’s not uncommon, even with domestic animals. Some mothers just aren’t good (at being) mothers,” explains Dr. Graham Crawshaw, the Toronto zoo’s senior veterinarian.
“Anyone who works with wild animals knows this isn’t uncommon or a reflection on this zoo, or zoos generally. It’s animals. Some animals do better than others. You can’t predict,” explained Crawshaw, who was reticent to discuss the issue with the Star.
Infanticide in the wild is common and occurs for a variety of reasons, says Mark Fitzpatrick assistant professor in the biology department at the University of Toronto, and an expert in animal behaviour, mating and aggression.
For example, in the case of lions, a new male might take over a pride and kill all the offspring.
“That will reset all the females into estrous, and he can maximize his reproductive success by mating with those females. That sort of scenario also happens with Colobine monkeys,’’ says Fitzpatrick.
But such behaviour is typically driven by male aggression, he says.
“Males are more likely to do the killing. With females it’s less common,” Fitzpatrick says.
One theory found in scientific literature on parental infanticide suggests it’s part of “normal’’ maternal behaviour where a female can adjust her litter size to suit her ability to raise offspring. Or, as Fitzpatrick notes, the female may do it because she simply wants to mate with a new male.
Animal rights activists charge that captivity is a major source of anxiety causing females to destroy their young.
“I think it’s fair to say that in most cases of infanticide, it’s related to stressors, whether it’s in the wild or in captivity,’’ says Zoocheck Canada director Julie Woodyer.
She says zoos claim that when the keep animals in captivity they’ve removed “stressors’’ that animals would face in the wild, such as lack of food.
“One of the primary reasons polar bears would kill their own cubs in the wild is because there isn’t enough food even for them to eat,’’ says Woodyer.
But this problem doesn’t exist in captivity, she says, yet moms such as Aurora are still experiencing difficulties rearing offspring, Woodyer notes.
“Once you remove those stressors these problems shouldn’t exist, but they do because zoos have created different kinds of stressors for the animals because they haven’t evolved to cope in that small environment. Polar bears are wide ranging carnivores that don’t do well when you confine them,’’ Woodyer argues.
To learn more about infanticide and maternal care issues with polar bears, the Toronto zoo is collecting the animals’ fecal and urine samples and trying to get a handle on their reproductive cycles and pregnancy.
Toronto is working with other zoos, which in turn are collaborating with biologists and researchers working in the wild. There are challenges however to studying maternal care in the wild because of the secretive nature of den sites for polar bears and other species.
Crawshaw argues one theory cannot fully explain infanticide and failure to rear issues involving females. He believes it’s largely tied to the disposition of the individual creature.
To make his point he describes the unusual maternal care case with Nokanda, the late female white lion who abandoned six of her cubs.
On two separate occasions she abandoned her newborns immediately after zoo staff separated them from her to do veterinary checks to ensure the offspring were healthy.
“(The first time) we put them back with her … she never touched the cubs again … She didn’t want anything to do with them. That was enough disturbance for her,’’ explains Crawshaw.
Zoo staff have separated moms from their cubs — other lions, tigers, cheetahs etc. — and those moms were absolutely fine once their pups were returned, he says.
In the second batch the following year, Toronto zoo staff waited 10 weeks before vaccinating the other set of Nokanda’s cubs — she’d been a good mother to them up to that point.
“We took them out, gave them their shots, checked them out (but) she never touched them again. That was that animal. We had to feed them. Now they’re big strapping animals.
“Again, each animal is different,’’ says Crawshaw.
As for Aurora, she was an inexperienced mom the first time she had babies, Crawshaw said, and was in an unfamiliar environment in the zoo’s new enclosure.
Aurora came to the zoo in 2001 after she and sister Nikita, both cubs at the time, were found wandering the wilderness alone, their mom apparently shot by a hunter. They were loaned to a polar bear habitat in Northern Ontario, and returned to Toronto in 2009.
In the past the zoo has had other polar bears who failed to raise their young, staff say.
Troubled mothers at the Toronto Zoo
• Female polar bear Aurora killed two of her cubs in October and had a third one taken away. She did the same thing in 2010, killing two newborn cubs.
• Tatiana, a Siberian tiger, gave birth to two cubs in 2000. One was found dead, the other alive but missing a leg that had been bitten off by mom. The cub was euthanized.
• Nokanda, a female white lion that passed away this summer, gave birth to four cubs in 1999 and two the following year, and abandoned all of them. Three in the first litter died, and one needed to be hand-reared. Two in the second litter required hand-rearing.
• Erin, a Himalayan tahr (wild goat), abandoned one of her two surviving babies, which needed to be hand-reared.