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Land Hermit Crab
credit: ZooFari/CCSA

Trading Spaces

Two contestants in this reality show have their claws out while they fight over new digs. Others travel a 22,000-mile annual circuit to be where the lighting is right. And still others must have a second (or third) home -- or even homes for every occasion. But this isn't a television show about trading spaces, it's life in the wild, where some animals change homes regularly. Usually this is part of the struggle for survival, but sometimes they just want a bigger place.

A Summer Place
Like so many people, a number of animals go for a complete change of scenery during summer. A number of birds prefer a summer place at the beach or in the woods or the mountains, and then a getaway to the tropics when temperatures drop and the days grow short. The great Gray Whales of the Pacific also like a northern summer and a southern winter. These magnificent mammals migrate up and down the West Coast, taking advantage of plentiful foods off the Alaskan and Siberian coasts in summer and fall, and of warm tropical waters off Baja California, Mexico, for calving in winter and spring.

Some people like a summer place with a lot of light, but nobody seems as committed to a sunny place as some Arctic Terns. These long-distance migrants travel about 22,000 miles a year in order to spend the Northern Hemisphere summer in the Arctic and the Southern Hemisphere summer in the Antarctic. This means that they are always summering in the land of the midnight sun. No other creature on earth is as exposed to as much daylight as the terns that travel this route.

Bearing the Winter
A number of northern animals that don't migrate to milder climates will search out a place to hole up for the winter. In the summer months Grizzly Bears make themselves a comfortable bed in a thicket, lining a shallow depression in the ground with a cushion of leaves, branches, and pine needles. Come winter, however, they trade in the open-air space for one that offers more protection from the elements. After all, they are going to sleep off the summer's excesses: some Grizzlies put on a 400-pound layer of fat before retiring for the winter!

The wintertime space may be in a cave, a hollow tree, or a hollow under a rock. Commonly believed to hibernate, bears sleep off the harshest part of winter, but their sleep is not deep and their temperature drops only a few degrees. (In true hibernators it drops to close to ambient temperature, and the "sleep" is much deeper.) Even Polar Bears den up for part of the winter, although they don't go for much of a décor change, trading an ice floe for the inside of a snow bank!

Shell We Move?
Hermit Crabs are constantly trading up. These little crabs need protection for their soft abdomens, so they ensconce themselves in discarded gastropod (snail) shells. A Hermit Crab must replace its shell with a larger one as it grows, but sometimes a crab will change shells for no apparent reason, except that it sees one that it likes better. In places where abandoned shells are uncommon, Hermits will fight with one another over a shell. Some will even forcibly remove a shell's inhabitant and move themselves in.

A move from one shell to another affects not just the crab, but also any creatures that share its home. One common co-inhabitant is known as Snail Fur, a hydrozoan that takes the form of a dense, furry mass, coating the shell of a Hermit Crab. The two live well together: The Snail Fur gets a free ride from one feeding area to another, and the Hermit Crab may gain some protection from the stinging cells of the hydrozoan.

A Home for Every Season
Bats spend much of their time roosting, which means resting or sleeping in a particular spot. Most of us think of bats as mainly cave or attic dwellers, but these flying mammals can be found in a wide variety of spaces, and some species seem to be trading spaces constantly.

Male and female bats often roost separately, and one or both sexes may be solitary roosters for part or all of the year. Since bats are active at night, their main roost in summer is the day roost. During the time that the young are born and developing, the day roost may also serve as a maternity or nursery roost, and is often occupied by thousands of females and young. Bats generally leave the day or maternity roost at dusk to feed. Some species then return to their day roost, while others occupy a night roost near the feeding area for part of the night, feed again before dawn, and then return to their day roost. For some species, the day roost becomes a hibernating roost (or hibernaculum) in winter, although most bats migrate to a separate hibernation roost.

So where are all these roosts? Just about everywhere! Solitary bats tend to live among the leaves or under the bark of trees or in a rock or building crevice. Social bats cluster in colonies in caves, mines, in hollow trees, in buildings, under bridges, or in other protected places, such as under slabs of rock or loose bark. Fruit bats sometimes break the midribs of large leaves by biting them so the leaves fold up, forming tents. One thing is certain: when it comes to trading spaces, bats know how to play the game!

Learn more about the roosting habits of North America's bats.