This small active songbird is 4 to 5 inches in length and has a brown head, back and tail, with rusty highlights, and darker bars that create a distinctive pattern. The belly is whitish to mottled brown. The tail is often held angled upwards, a common posture in all wrens. This wren has the widest distribution of any other American bird, occurring from Canada to the tip of South America. They breed throughout most of the United States and through most of New Mexico, only excepting the Gulf Coast States. Winter range includes the southern portions of Gulf Coast states and into Mexico.
House wrens feed on a wide variety of insects and other invertebrates as they forage in low branches of trees and brush, and often on the ground. Both males and females may be promiscuous, having multiple mates and producing two broods per year. House wrens prefer brushy habitats where they nest in cavities, such as woodpecker holes. Males aggressively defend chosen nesting sites, often chasing away larger cavity nesting birds. They will also readily accept nest boxes. Males start construction of several cavity nests, using twigs, leaving the female mate to select one to finish out with her choice of grass, feathers, animal hair and other accoutrements.
Females sometimes add spider egg sacs to nests, where the spiders have been observed in lab settings to help reduce the mite and parasite population that tends to accumulate in nests. Males are also aggressive toward other species and may destroy eggs of other birds by puncturing the shells. House wrens produce clutches of 2 to 8 eggs. The clutch size and production of two broods per season, as well as their promiscuous behavior probably offset losses from other wrens and the many other potential predators, such as cats, woodpeckers, foxes, raccoons, snakes, squirrels and other rodents.
The song of males is a rapid musical warbling, beginning with a series of buzzy, notes, followed by 1 to 2 seconds of jumbled warbling. Females also sing, and research has shown that female singing reduces nest attacks by other wrens and promotes nest productivity. The oldest recorded House wren was a 9-year-old, based on recapture of a previously banded bird in New York.
The temperature of eggs in nests has been shown to be critical to embryo survival. Temperatures above 106 °F or below 65 °F will kill embryos. This temperature sensitivity is probably the primary limiting factor on nesting range in the U.S. and a predictor of how the breeding range is expected to shift northward as the climate continues to warm. The Audubon Society expects a reduction of breeding range in the southern parts of Midwestern states and an expansion of the range across the northern range in Canada in the future.