Animals have three main strategies to survive the freezing temperatures of winter: migrating, remaining in place and resisting the cold, and reducing body temperature and metabolic rate in a state called torpor.

These cold-survival strategies are often studied in isolation by biologists and treated as mutually exclusive alternatives: An animal species is described as either migrating or hibernating (torpor includes both dormancy and hibernation), for example.

But in reality, many animals combine multiple strategies to beat the cold, University of Michigan evolutionary biologist Giorgia Auteri explains in the journal Biology Letters.

Warm-bloodedness is a cold-resistance strategy used by mammals and birds, but some of these creatures also use a combination of migration and torpor. For example, many high-latitude bats and birds such as swallows, hummingbirds and warblers use both migration and torpor, Auteri said.

Sometimes, strategies are split among members of a species. Some blue jays may migrate south while most state put, and individual eastern chipmunks may shift from torpor to cold resistance when food caches are abundant. The common green darner dragonfly exhibits tradeoffs between migration and torpor, with more northern populations being exclusively migratory.

“Each cold-survival strategy exists not as a binary but on a spectrum,” said Auteri, who proposes an integrated conceptual framework for examining cold-survival strategies in the Biology Letters article, which was published online May 4.

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