Carolina Wren: Nest and Eggs

Adult Carolina wren. Photo: Dennis Church.

Carolina wrens (Thryothorus ludovicianus) are familiar birds not because they are abundant but because they are vocal and have a loud, melodious song. They can be found anywhere there is a patch of vegetation and forage for food in people’s yards, patios, and inside sheds and garages. Coraline wrens usually nest in hanging boots, open boxes, pockets of hanging coats, and enclosures. This article is intended to aid in identifying Carolina wren nests and eggs.

Carolina wren breeding facts

Breeding PeriodMid-March through late September.
Nest typeNests built outside cavities have a dome shape and have a side entrance. Nests built inside a cavity consist of a cup of 2.3 to 2.7 inches across.
Substrate & LocationInside or outside a cavity or enclosure. Typically within 4 to 8 feet from the ground. 
Nesting ActivitiesMale may build multiple pilot nests. The female chooses the nest. Both sexes build the nest and rear the young. The female alone incubates the eggs.
Egg DescriptionWhite to creamy-white with reddish-brown dots more concentrated toward the wide side of the egg.
Egg Length and widthApproximate length 0.74 inches, width 0.58 inches..
Egg-layingIt begins when the female lays the penultimate egg. During the egg-laying period, the female lays one egg every day.
Clutch sizeTypically 4-5 eggs, rarely up to 8 eggs.
Number of broodsDouble brood. Three broods are likely in the southern part of its range.
Incubation PeriodTypically 14 days ranging between 13 to 18 days across the species range.

 

Breeding range and habitat

The Carolina wren is a year-round resident in eastern North America. It is also found in the northeastern portion of northern Mexico and the Yucatan Peninsula.

Carolina wrens prefer lightly wooded areas with dense undergrowth. In residential areas, trees with shrubs, undergrowth, and ornamental plants are habitats for the Carolina wren.

Breeding range of the Carolina Wren. Source: BirdsoftheWorld.org.

Migration and social behavior

Where they occur, Carolina wrens are year-round residents. 

They become less vocal during the colder months of the northern states, but they remain in the area and are not known to undergo annual movements in response to cold weather.

Wrens form long-term pair bonds and often forage within a short distance of each other during the breeding and nonbreeding seasons. While foraging for insects, wrens move about restlessly, usually within 0 to 16 feet from the ground.

Breeding Period

Carolina wrens breed within a relatively long period that encompasses mid-March through late September. During this period, wrens generally attempt two broods per breeding season. Birds in the southern part of its range may attempt three broods.

A breeding attempt lasts approximately 57 days, counting from the day the female lays the first egg until the fledglings become independent from the parents.

The appearance of a Carolina Wren’s nest

The nest appearance depends on where birds decide to nest. Nests outside of a cavity or an enclosure have a dome shape with a side entrance. The nest’s roof, sides, and entrance hole have a messy appearance. 

Carolina wren nest, built in an empty bucket. Photo: Denise Rouse.

In nests placed inside an enclosure or cavity, the roof is usually not present, and the entrance hole becomes the nest’s entrance.

The materials used to build the nest include dry grasses, dead leaves, twigs, pieces of plastic, and strings. The cup is lined with hair, mammal fur, and even bits of plastic.

Nesting habits

Fledglings leave the natal territory after becoming independent from their parents. It is unknown how far they travel from their natal territory and when they form a pair to breed during the next breeding season.

In terms of nest-site selection, Carolina wrens are pretty flexible. Their nest does not require a cavity or enclosure, unlike other cavity-nesting birds. 

If there is a suitable cavity, they use it; if there isn’t one, they use anything that looks like one. If not, birds can nest outside of a cavity or enclosure.

Nest site selection

Carolina wren nest built in a hanging hiking boot. Photo: Nagasaki Osada.

Carolina wrens can build a nest in almost anything that resembles an enclosure or semi-enclosure. Nests are typically built in natural cavities, tree forks, broken trunks, inside vines and tangled branches, and abandoned woodpecker cavities.

Wrens do not shy away from artificial structures and have nested in hanging boots, shoe boxes, flower pots, hammocks, and even in the motor of parked vehicles.

Bird nests found in backyards, tool rooms, and sheds are likely Carolina wren nests. 

Nest building

Male wrens may build multiple nests without completing them. A breeding attempt begins when the female selects one of the nests. 

Both the male and female contribute to building the nest after it has been selected. Often, the female stays in the nest to arrange the material that the male brings. It can take a pair of birds four days to build a nest.

Females build a cup that measures 2.3 to 2.7 inches across, lined with fine fibers and mammal fur if available. Snakeskin may be used in a nest as a nesting material.

 Egg appearance

The eggs are white to creamy white with reddish-brown spots on the wide side. The eggs in some clutches may have fewer reddish-brown spots and appear paler.

Close-up view of Carolina wren eggs and size compared to a Nickel.

Except for differences in pigmentation in some eggs, the pattern is similar across nests.

An egg of a Carolina wren has a length of 0.74 inches and a width of 0.58 inches.

Egg Laying

The female Carolina wren lays eggs as early as the last week of March. After the nest is complete, the egg-laying period begins. 

Every morning, the female lays one egg. 

Every nesting season, Caroline wrens have two broods. Birds in the south may have three broods.

Clutch size

Carolina wren incubating eggs. The long pale eyebrows are a good identification field mark. Photo: Downs Family Farm.

Carolina wren females typically lay clutches of 4 to 5 eggs, but nests may contain up to 8 eggs. 

Incubation of the eggs

Incubation is not initiated until the female lays the next-to-last egg. Incubation is done by the female day and night, and she only takes a break during the day for basic needs. 

The male brings food to feed the female while she sits on the eggs. Nevertheless, the female forages for food on her own when she takes a break.

Incubation period

Carolina Wren females incubate their eggs for an average of 14 days, ranging from 13 to 18 days. Incubation periods in the south are shorter than in the north.

References:

  • D’Orazio, K. A. and D. L. H. Neudorf. (2008). Nest defense by Carolina Wrens. Wilson Journal of Ornithology 120 (3):467-472.
  • Horn, J. C. (1984). Short-term changes in bird communities after clearcutting in western North Carolina. Wilson Bulletin 96:684-689.
  • Wood, D. R. and W. A. Carter. (2006). Carolina Wren nest successfully parasitized by House Finch. Wilson Journal of Ornithology 118 (3):413-415.

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