Wren Housing & Nesting
Nest Building: Carolina Wrens begin breeding as early as mid-March in some regions, in early April in others. Males build multiple nests within the territory, but females select the final nest site. Nests are usually built in enclosed areas: natural cavities, vine tangles, upturned roots, tree stumps, or abandoned woodpecker holes. They also nest in nest boxes and other, less-natural nooks and crannies such as mailboxes, glove compartments, tin cans, and old shoes.
Both sexes construct the nest. It can take a pair from four days to over a week to complete a nest. Nests, dome-shaped with a side entrance, are made from bark strips, dried grasses, dead leaves, sticks, pine needles, mosses, feathers, straw, shed snakeskin, paper, and string. Nests are lined with hair or fur. They are rarely more than 12 feet above the ground.
Egg Laying: The eggs are creamy white to pinkish white, heavily spotted with purplish brown to rusty brown flecks. Flecking can form a wreath around the large end of the egg. Eggs are laid in the morning, one egg per day. A complete clutch usually contains four to five eggs but may contain as many as eight. Carolina Wrens are sometimes parasitized by Brown-headed Cowbirds.
Incubation: Only the female incubates; she begins the day the last egg is laid. Females are tight sitters, not readily flushing from the nest. The incubation period lasts 12 to 14 days. During this time, the male often brings food to the nest for the female. Compared to other passerines, Carolina Wrens spend unusually long periods on the nest, taking few breaks. For example, during incubation House Wrens leave the nest 27 to 43 times a day, whereas Carolina Wrens leave only six to seven times a day.
Nestling Care: The eggs hatch synchronously, within 24 hours of each other. For the first four days after hatching, the female broods the young. Nestlings are fed immediately after hatching, and the male brings food to feed the family. As the young grow, the female broods only at night and helps the male collect food and feed the young during the day.
After 12 to 14 days, the parents coax the young out of the nest. The nestlings usually leave the nest in the morning, hopping and flying short distances. The fledglings stay together and are fed by both parents. If the female begins another nesting attempt, however, the male alone cares for the fledglings. Four weeks after fledging, the young are independent.
Carolina Wrens in northern regions usually raise two broods, whereas birds living in southern areas can raise three.
More About Wrens
The size of a small sparrow, the Carolina Wren is a relatively large member of the wren family. Male and females look alike, but males are slightly heavier and have longer bills, wings, and tails. The back is dark rusty brown, but the rump is bright rust. The breast and belly are buffy and unmarked; the flanks are cinnamon. The throat and chin are white, and the prominent eye stripe is white to buffy white. The bill is dark above and yellowish below. Juvenile plumage resembles adult plumage but is paler.
Distribution and Breeding Habitat
Carolina Wrens are commonly found in the southeastern United States. They range as far north as southeastern Ontario, Canada, and as far west as eastern Oklahoma, Nebraska, and Texas, USA. Their southern range extends to the northeastern corner of Mexico and parts of Central America. Isolated populations exist outside of the range boundaries, as the species is slowly expanding its range north and westward.
These shy wrens require dense shrub and brushy habitats for concealment. As a result, they are more often heard than seen. They are common in forests, clear cuts, and wooded suburban areas with thick underbrush. They prefer moist bottomland forests and swamps over dry upland woods.
Carolina Wrens are ground foragers, hopping and flitting on the ground turning over leaf litter and investigating upturned tree roots to find a variety of food items. The diet mainly consists of insects, including beetles, caterpillars, moths, crickets, bees, and ants. These birds are also seen hitching up tree trunks in the manner of creepers and nuthatches, probing the bark for prey items such as snails and spiders. The diet rarely includes seeds, acorns, or other vegetable matter.
Pair Formation and Territoriality
Carolina Wrens are monogamous and maintain pair bonds and territories year-round. Both sexes use songs and calls to defend territory boundaries. All nesting, foraging, and feeding of nestlings occurs within the territory. Pairs may bond any time of the year, sometimes as early as the fall of a bird’s hatch year. Males court females intensively, hopping stiffly around them, puffing their feathers, and erecting their tails like a turkey. Males may offer food to the female during courtship and the early stages of nest building. Once formed, pair bonds are lifelong, but a bird may find a new mate to replace one that has died.
Winter Movement and Dispersal
Carolina Wrens are non-migratory. Pairs remain together on territories year round, but in periods of harsh weather birds move off territories in search of food. Nest boxes containing straw can provide roosting sites for individuals during harsh winters.
After reaching independence, young Carolina Wrens move off the natal territory. They stay nearby, setting up territories near their natal area.
Source: Cornell Lab of Ornithology