Bat Swarms of Colorado

When we think of bats, the environment that first springs to mind is that of a cave. While there are a number of bats that roost in trees during the day, a great many are, indeed, cave-dwellers. Because caves aren't all that common in most places, bat colonies within them can be huge, which creates something of a problem when they all try to fly out in the evening. But, if you watched a bat cave throughout a year, in most cases, the activity level would change radically as the seasons progressed.

This is largely because most bats eat insects. In temperate climates, insects aren't around much during the winter; in many cases they've died off and left their eggs to hatch the following spring when the weather has improved. Any animal that relies heavily on eating insects to survive has to deal with this scarcity somehow. Insect eating birds, such as swallows and thrushes, cope with the problem by migrating in the winter, heading to warmer climes where insects are still common. There are some bats that do exactly this - for example, the hoary bat migrates annually between Canada and the southern US - but more commonly, they deal with the absence of food by hibernating.