How Long Do They Live?
Zoo Scientists Calculate Animal Life Expectancies
Birth to death. That's the scale of any life cycle, encompassing the beginning, the end and all the experiences in between.
Species vary considerably in their life cycles, of course. A 7-year-old Guam Micronesian kingfisher is middle aged while a 7-year-old chimpanzee is just entering puberty. A new generation of cactus mice can appear every couple months while a developing eastern black rhino spends more than a year in the womb.
Beyond that, every individual has its own life cycle. Just like humans, some may be cut short before their prime; others, like chimpanzee Keo, thrive well past what’s thought to be old age. So how do you measure an animal’s life? How do you know, as people often ask, if an individual at the zoo lived “long enough”?
You can’t just use the longest-lived members of a species as the measuring stick. They might be outliers, individuals whose life history falls far outside the norm. The record for human longevity is 122 years, but few of us think we’ll come close to that mark.
To answer the question scientifically, the zoo community turned to a group of biologists led by Vice President of Conservation & Science Lisa Faust, Ph.D. With additional support from Columbus Zoo and Aquarium, these experts scoured decades of population records from institutions throughout the Association of Zoos and Aquariums (AZA). In doing so, they were able to define median life expectancies for 110 species.
Instead of representing a maximum, like the 122-year figure above, median life expectancy is more like a midpoint. It’s the age at which just as many individuals continue to live as have died. For a Bactrian camel in an AZA zoo, that’s 17.9 years. For a Pallas’ cat, it’s 8.6.
As zoos collect more data, our experts hope to expand the number of species with calculated median life expectancies. Right now, though, these figures give us a scientific way to discuss how long animals are likely to live…even as every individual follows its own unique path.
By James Seidler • Published July 17, 2014 • Originally published in Spring 2014 Lincoln Park Zoo Magazine