The following information from the National Geographic Society website very aptly summarizes the basics of Carolina Wren biology:
The Carolina wren is an adaptable dweller of forestlands, swamps, farms, and tree-filled human communities.
Carolina wrens (Thryothorus ludovicianus) are small but very vocal animals. Males are especially outgoing and are the only ones to produce songs. They employ one of the loudest songs per volume of birds. They are apt to sing anytime and anyplace they happen to be.
Carolina wrens are usually found in pairs, and each pair stays on its home territory all year long. Because these wrens cannot survive cold winters, they tend to live in southern climes, and are the official state bird of South Carolina. They are found as far north as the Great Lakes, and warm winters spur them to extend their range northward. However, when colder years arrive, many northern birds are unable to survive and fringe populations plummet.
These large wrens feed on insects, larvae, and spiders but also eat berries and fruit. They forage on or near the ground and hop along far more often than they fly. They use their bills to poke about and search for hidden meals and try to remain close to brush in which they can hide.
Carolina wrens are monogamous, and breeding pairs may stay together for years. They work together to construct nests—which may be found almost anywhere. Wrens nest in natural locations such as branches, tree-holes, and stumps but also frequent windowsills, mailboxes or other attractive human-made spots.
Females lay about four eggs and incubate them for two weeks while their mates bring them food. Both parents feed their chicks for an additional two weeks before they gain independence. A mating pair of Carolina wrens may have several broods each year.
Carolina Wrens are largely restricted to the southeastern and eastern United States as this range map suggests. The first one I ever saw was singing its heart out along the route of a Breeding Bird Survey transect route in Pepin County Wisconsin in June 1974. There have been many Carolina Wrens since then!
One of the most characteristic aspects of Carolina Wrens is their distinctive voices. The mnemonics most often used to describe their voice are either "So Pretty, So Pretty, So Pretty....." or "Tea Kettle, Tea Kettle, Tea Kettle....." You can hear their voice in one of its more common forms at this link. This recording is one of about a zillion voices that Carolina Wrens possess.
Since moving to Sarasota in February 2009, I have been keeping track of the voices of several Carolina Wren males in my 'hood. Most of them sing the characteristic So Pretty and Tea Kettle songs. However there is one male here who occasionally mixes it up and instead of doing what the book says he should sing, this one says "Cheeseburger, Cheeseburger, Cheeseburger...." over and over and over again. I've never heard one do that voice.
Not long ago my friend Jon Andrew commented on my description of the voice suggesting that I should sober up when listening to it. However thats exactly what the bird sounds like it says. And then today, as I took off on my daily 16 mile bike ride, I heard and then watched a Northern Mockingbird singing a perfect "Cheeseburger, Cheeseburger, Cheeseburger...." I can only imagine that he learned it from the Carolina Wren in my backyard.