The Carolina Wren (<i>Thryothorus ludovicianus</i>) is one of several species of wrens found in the Carolinas. This small-bodied bird is found year-round through much of the eastern United States and south into Mexico (Peterson and Peterson 2002). It is the only wren in eastern North America that does not migrate to warmer climates in the winter (Sibley 2000). This overwintering habit makes the species vulnerable to harsh winter temperatures, particularly in the mountains of the Carolinas and in the northern portion of the bird's range. Many researchers have concluded from studies in the colder portions of its range that winter survival is directly related to low temperatures (Brooks 1936; Root 1988; Link and Sauer 2007). Other researchers have suggested that it might be linked to the availability of food resources (Job and Bednekoff 2011). Ultimately, both factors contribute to the bird's range, and changes in climate temperature have been directly correlated to the gradual northward range expansion of the species (Job and Bednekoff 2011).