Winter wrens have a range of approximately 5,430,000 square kilometers with about 36,000,000 individuals. They are found in the temperate northern hemisphere, including Europe, much of Asia, and North America. There are some gaps in this range, including a large part of Turkmenistan. Winter wrens are most common in eastern and western North America and Eurasia.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); mediterranean sea (Native )

Other Geographic Terms: holarctic

Winter wrens are tiny brown birds with dark barring on their wings, tails, and ventral surfaces. They have a light stripe just above their eyes and their throats are lighter than the rest of their bodies. Juveniles are darker than adults and the sexes look the same. They have a narrow bill and a short tail which usually points upward.

Winter wrens have round, short wings with strong distal feathers. These features are adaptations to living in dense vegetation. Round, short wings require less effort and room to suddenly take off or stop and they are easier to maneuver within obstacles. Having heavier, stronger feathers at the ends of their wings protects them from breakage when they inevitably smack something in their crowded environment.

Winter wrens sexes can be distinguished during the breeding season by the presence of either a brood patch (female) or a cloacal protuberance (male). Age can be determined by the number of spots on their fourth primaries.

A species' average basal metabolic rate is influenced by several factors, including size and plumage color. Birds which eat mainly invertebrate prey generally have intermediate basal metabolic rates, compared to similar birds eating different diets. Temperate species average higher BMRs than tropical species and flighted birds are higher than flightless ones. Winter wrens average 0.60 kJ/h basal metabolic rate.

Range mass: 8 to 12 g.

Range length: 8 to 12 cm.

Range wingspan: 12 to 16 cm.

Average basal metabolic rate: 0.60 kJ/h cm^3 oxygen/hour.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

• Terrestrial

Winter wrens are found in a wide range of habitats. They prefer deciduous forests, but they are also common in pastures, farms, scrub forests, coniferous forests, towns, and villages. They also occur on heath, grasslands, marshes, and in croplands. Winter wrens prefer thick vegetation close to the ground.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: forest ; scrub forest ; mountains

Wetlands: marsh

Other Habitat Features: urban ; suburban ; agricultural ; riparian

Winter wrens are insectivores that eat a wide variety of invertebrate prey. They hunt for food on the ground. In addition to insects and their larvae, they also regularly consume millipedes and spiders. If they are in riparian areas they may prey on aquatic invertebrates. Their small size allows them to forage in places where other insectivorous birds cannot successfully forage.

Animal Foods: insects; terrestrial non-insect arthropods; aquatic crustaceans

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)

Winter wrens are important members of the ecosystem because they eat insects and are food for larger predators. In addition to these roles, they are parasitized by both invertebrates and vertebrates. They suffer from feather mites of the family Proctophyllodidae, which includes the genera Proctophyllodes and Monojoubertia. They are subject to nest parasitism by common cuckoos, Cuculus canorus.

Commensal/Parasitic Species:

• feather mites (Proctophyllodes)
• feather mites (Monojoubertia)
• common cuckoos (Cuculus canorus)

Domestic cats, which are ubiquitous anywhere humans exist, are major predators of native animals, including winter wrens. Northern harriers (Circus cyaneus) eat adult wrens. Nests are preyed on by many animals, including crows and jays and weasels. Interestingly, crows and jays destroy empty nests in addition to ones containing eggs or nestlings.

Winter wrens have a few adaptations to counteract possible attacks by predators or nest parasites. Cryptic coloration makes them and their nests hard to find, and their habit of building several nests makes the real nest harder to locate. They also avoid nesting near established nests. Despite these countermeasures, cuckoos in Germany heavily parasitize them.

Known Predators:

• domestic cats (Felis catus)
• Eurasian jays (Garrulus glandarius)
• common magpies (Pica pica)
• least weasels (Mustela nivalis)
• northern harriers (Circus cyaneus)

Anti-predator Adaptations: cryptic

Male winter wrens use song to establish and maintain their territories. Their songs are variable and fast, using between 15 and 40 notes per second, and the entire song lasts 5 to 10 seconds. They are impressively loud. Winter wrens use ten times as much power to deliver their songs as roosters would if they weighed the same amount. They also use other calls, which are only one or two notes.

Male winter wrens listen to the songs of other wrens in order to know who and where they are. Their songs are high-pitched, averaging around 5500 hertz, so they are subject to a lot of deterioration as they travel farther from the singing wren. To avoid some of this degradation, wrens choose high places from which to sing so their messages will travel farther with less degradation of the signal. These perches are generally 1 to 4 meters high. Winter wrens also use singing perches to listen for the songs of other males. Winter wrens seem to be able to understand and respond to even highly degraded signals from other male winter wrens. They can determine how degraded the song is, indicating to the listener how far away the singer is. Winter wrens react more aggressively when they know the singer is close rather than if they know he is far away.

Singing is most important just before and after dawn. This is the time when intruding males will attempt to steal territory so a defending male must be ready to meet his challenger with a song. Dominance is determined by who sings the best songs. Females listen to these contests and, if they like the intruder’s song, they may sneak off afterward and seek extra-pair copulations. Males who have defended their territory recently sing more than males who have not. However, they sing less in cold weather, especially after cold nights.

Communication Channels: visual ; acoustic

Winter wrens typically live only two years, but birds which survive longer than two years can still be reproductively active. Breeding males have been found up to 4 years old. The longest recorded lifespan in the wild was 6 years and 8 months.

Average lifespan

Status: wild: 6.75 years.

Average lifespan

Status: wild: 2 years.

Breeding season is mid-March to mid-August. Males either return each year to their previous breeding territory or remain on site year-round. Males in poor territories generally only keep one mate, but males in better areas can be polygamous. Males establish territories by singing and displaying and they defend these territories very aggressively against intruding males. Familiarity with their sites allows them to know the best places for resources and food. They build several nests on their territories, which can be used for shelter or by a mate forming a nest. Males build up to twelve nests, but average six.

Females are as not faithful to the same locations year after year. Unlike males, which defend territories, females rely on broader home ranges which they do not defend. They search in their range for a suitable male. Even when a female joins a male, only the male will defend the territory.

Males initially attract females with songs. When a female arrives, the male will give her a tour of all the cock nests in his territory. While giving her the tour, he displays in and around his nests. Females typically examine several nests before choosing and prefer males whose territories contain more nests. When a female chooses one, she will settle in and provide the nest with feathers and hair to make it suitable for brooding. If her nest is destroyed by a predator, she will usually abandon her mate and his territory and find a new mate. Polygamous males continue to try to attract females while his established mate or mates try to raise their broods. Males can have up to 9 mates.

Older males often begin building nests earlier than younger ones, allowing them to build more nests. Females do not seem to mate selectively with older males, however, because too many factors determine how many nests a male has on his territory. Some males have more nest building ability than others and this ability can outweigh age benefits when it comes to accruing nests.

Mating System: monogamous ; polygynous

Males build nests (called cock nests) of anything they find, including moss, feathers, twigs and grass. They often build it in a hole which may have been dug by the wren or found. They may also build on branches. Nests are domed and have an entrance hole. Males begin building cock nests up to a month before females begin laying eggs. Individual males vary widely in when they begin building, with the earliest building two months before the latest. After settling in to a nest site, females produce about 5 to 7 eggs, which are white with reddish brown spots. Eggs are 1.3 grams in weight of which 6% is shell.

Breeding interval: Winter wrens breed once yearly.

Breeding season: Breeding season is from mid-March to mid-August.

Range eggs per season: 1 to 9.

Average eggs per season: 5-7.

Range time to hatching: 16 to 18 days.

Average birth mass: 1.3 (6% is shell) g.

Range fledging age: 15 to 18 days.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): 1 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Females incubate the eggs and the young hatch at an altricial stage with some downy feathers. Raising the brood is generally the female’s responsibility, but some males help. Monogamous males spend more time on domestic activities, while polygamous males continue to spend time on singing and courting females. Some males don't care the their young at all, some males provide an equal amount of care as females. Males are capable of raising broods on their own.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)

Accidental visitor.

Least Concern.

With 36,000,000 individuals and no serious trends of declining populations, winter wrens are not considered a species of concern. Populations of winter wrens in Britain are increasing.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

There are no known adverse effects of winter wrens on humans.

Because winter wrens are small, insectivorous birds, they are affected by cold weather more than many other bird species. Their population levels drop when temperatures are consistently too low. As a result they are used as indicators of changing climate. They may help to control pest populations in areas of human habitation.

Positive Impacts: research and education; controls pest population