Why Do Birds Live Longer Than Turtles?
The key indicator for animals may be total energy expended over a lifetime
Conventional wisdom in longevity studies used to be that the life span
of a creature was roughly proportional to its body mass and heart
rate—the big, slow elephant outlives the quick, small mouse. New
research, however, presents a more complicated picture. Bats and birds,
for instance, are small but tend to live longer than many larger
creatures. Moreover, when scientists look within particular species,
size does not correlate well with life span, although fast growth is
often associated with reduced longevity. To some degree, resting
metabolic rate does correlate, but for animals total energy expended
over a lifetime may be the best indicator of all. Definitive answers in
this field can be slow in coming, partly because the studies take a long
time to do—a typical Galápagos tortoise, for instance, can outlast a
scientist's career. And don't hold your breath for insights into the
extreme life span of the bristlecone pine.

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