Washington, March 2 (IANS) The squirrels littering your lawn with acorns as they bound overhead will live to plague your yard longer than the ones that aerate it with their burrows, according to a study.

Scientists from the University of Illinois at Urbana-Champaign (UI-UC) know from previous studies that flying birds and bats live longer than earthbound animals of the same size.

Milena Shattuck and Scott Williams, doctoral candidates of anthropology at UI-UC, decided to take a closer look at the relationship between habitat and lifespan in mammals, comparing terrestrial and treetop life.

The two hypothesised that, like flight, treetop or arboreal dwelling reduces a species' extrinsic mortality -- death from predation, disease and environmental hazards; that is, causes other than age.

'One of the predictions of the evolutionary theory of ageing is that if you can reduce sources of extrinsic mortality, you'll end up exposing some of the late-acting mutations to natural selection, and therefore evolve longer lifespans,' Williams said.

Williams and Shattuck found that for arboreality, the theory holds. Mammals who spend the majority of their time up a tree enjoy longevity over those who scurry along the ground.

The pattern holds consistent both among all mammals, and also in specific classes the pair studied, such as tree squirrels versus ground squirrels.

However, the pair also uncovered two classes of mammals that buck the longevity trend -- marsupials, such as kangaroos, and primates, including ground walkers such as gorillas and humans and their branch-swinging counterparts.

Aloft or not, these groups show no significant difference, although primates in general tend to lead long lives, said a UI-UC release.

The findings were published in the Proceedings of the National Academy of Sciences.