Why bats can't handle extreme climates

Though among the most numerous of mammals, bats are restricted to moderate conditions and habitats—remaining nocturnal to avoid the heat and migrating or hibernating en masse to avoid the cold. To thrive in colder climates, bats would need better insulation, but that in turn would require a better way to stay cool in flight.

Thor Hanson, Feathers: The Evolution of a Natural Miracle (New York: Basic Books, 2011), p. 114