Study raises worries for zoo-born elephants

Study of captive-born females finds big survival gap between zoo natives and elephants in native ranges

A controversial new study raises the possibility that female elephants have been living half-lives if they’re born in zoos.

For the African species, zoo-born female elephants tend to live 16.9 years in European zoos, says Georgia Mason of the University of Guelph in Canada.  Their counterparts in Amboseli National Park in Kenya who die of natural causes live an average of 56 years. When adding in human-caused deaths in Amboseli, the comparison is 16.9 in captivity to 35.9 years in the park, she and her colleagues report in the December 12 Science.

For the Asian species, the news isn’t much better. Zoo-born females averaged 18.9 years in European zoos, but those living in Myanmar’s logging areas lived an average 41.7 years.

“Within the group of authors we have different attitudes toward zoos,” Mason says. What the group agrees on, she says, is that zoos should be able to demonstrate that, if they’re going to keep elephants, they should do so without heightening mortality risks.

To compare elephant survival, Mason and her colleagues looked at records spanning four decades from more than 200 zoos keeping a total of nearly 800 elephants, both African and Asian. Amboseli elephants have been tracked since the early 1970s, and Myanma Timber Enterprise supplied data on some 2,900 elephants.

Life span depends on how you do the numbers, says population biologist Kevin Willis of the Minnesota Zoo in Apple Valley (which does not keep elephants). In 2004, he and Robert Wiese of the San Diego Zoo published life spans for female elephants living in North American zoos: 33 years for African elephants and 44.8 for Asian elephants. For European zoos, Willis and Wiese calculated that female Asian elephants lived an average of 47.6 years.

Willis suggests that one reason for the differences between the studies is that the 2004 work combined wild-caught and captive-born animals. Elephants from Asia’s natural population do pretty well with zoo life, but Mason’s study just compares captive-born elephants.

Also, Willis says, his study didn’t include deaths during the first year of life because he was making his analysis comparable to an earlier one.

At the same time, Willis does say that his sense of the numbers suggests that zoos probably haven’t yet figured out how to keep African elephants in captivity in a way that matches their full survival in the wild.

Mason’s study “is of limited use,” says Steve Feldman of the Association of Zoos and Aquariums. “They’re arguing against practices that are no longer current.”

Of course zookeepers have changed the ways they care for elephants during the four-plus decades covered in the study, Mason says. The study did find some encouraging trends.

But she and her colleagues worry that care may not have improved enough yet. African females in 2005 still faced a risk of dying from natural causes that was 2.8 times higher in zoos than in the protected native ranges. For Asian elephants, the study did not detect an improvement, Mason says.

Exactly what’s causing the difference in survivorship will need more analysis, Mason says. She proposes that obesity and stress are major factors.

For Asian elephants, infant mortality rates at zoos were higher too, and being born in zoos instead of brought in from the wild increased the risk of early death.  That too might be an effect of stress, but in the mothers, Mason suggests.

Birth rates in zoos are too low for the zoo populations to be self sustaining. “Currently zoos are net consumers of elephants, not net producers,” Mason says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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