The Black-capped Chickadee (Poecile atricapillus) is a small, North American songbird, a passerine bird in the tit family Paridae. It is the state bird of both Maine and Massachusetts in the United States, and the provincial bird of New Brunswick in Canada. It is notable for its capacity to lower its body temperature during cold winter nights, its good spatial memory to relocate the caches where it stores food, and its boldness near humans (they can feed from the hand).

Taxonomy

Though often placed in the genus Parus with most other tits, mtDNA cytochrome b sequence data and morphology suggest that separating Poecile more adequately expresses these birds' relationships.^[1] The American Ornithologists' Union has treated Poecile as a distinct genus for some time.

The genus name Poecile has often been treated as feminine (giving the species name ending atricapilla); however, this was not specified by the original genus author Johann Jakob Kaup, and under the ICZN the genus name must therefore be treated by default as masculine, giving the name ending atricapillus.^[2]

Description

The Black-capped Chickadee has a black cap and bib with white sides to the face. Its underparts are white with rusty brown on the flanks. Its back is gray and the tail is normally slate-gray. This bird has a short dark bill (8.0-9.5 mm), short rounded wings (63.5-67.5 mm) and a long tail (58–63 mm). Total body length is 12–15 cm (4.7–5.9 in), wingspan is 16–21 cm (6.3–8.3 in) and body mass is 9–14 g (0.32–0.49 oz).^[3] Sexes look alike, but males are slightly larger and longer than females.

Although range can generally be used to separate them, the Black-capped Chickadee is very similar in appearance to the Carolina Chickadee. The Black-capped is larger on average but this cannot be used reliably for identification. The most obvious difference between the two is in the wing feathers. In the Black-capped Chickadee, the wing feathers have white edges that are larger and more conspicuous than those of the Carolina Chickadee. Overall, the Carolina appears slightly paler colored whereas the flanks of the Black-capped can appear to have a trace of off-yellow or rusty coloration. Also, the Black-capped generally has a more "ragged" looking black bib, whereas the bib of the Carolina has a more smooth-edged look. These subtle features are often even more vague in populations around where the Black-capped and Carolina overlap in range (possibly the result of hybrids) and the two cannot always be distinguished to species. The two species were formerly thought to be easily distinguished by call, but they often learn each other's vocalizations where their ranges overlap (their point of overlap is a narrow band that runs along the east-central United States, with the Black-capped Chickadee to the north). A bird located near the zone of overlap that sings both songs, or sings "odd-sounding" songs, cannot be positively identified solely by voice in the field.^[4]

Distribution and habitat

The black-capped chickadee is found from coast to coast, from the northern half of the United States in the south, to James Bay, the southern edge of the Northwest Territories and the Yukon, and the southern half of Alaska in the north. In winter it may wander outside of this range, both to the north and south.

Its preferred habitat is deciduous woods or mixed (deciduous/coniferous) woods. It is also found in open woods, parks, and suburban areas. Habitat segregation is the principal factor that separates the Black-capped Chickadee from both the Boreal Chickadee in the north and the Chestnut-backed Chickadee in the Pacific northwest (these two species prefer strictly coniferous forests). Altitude also separates the Black-capped Chickadee from the (higher) Mountain Chickadee in the western mountains and the (lower) Carolina Chickadee in the Great Smokey Mountains.

Diet

Chickadees will take food such as seeds from feeders and trays over to a tree branch to hammer them open.

Insects (especially caterpillars) form a large part of their diet in summer. The birds hop along tree branches searching for food, sometimes hanging upside down or hovering; they may make short flights to catch insects in the air. Seeds and berries become more important in winter, though insect eggs and pupae remain on the menu. Black oil sunflower seeds are readily taken from bird feeders. The birds take a seed in their bill and commonly fly from the feeder to a tree, where they proceed to hammer the seed on a branch to open it.

Like many other species in the Paridae family, Black-capped chickadees commonly cache food, mostly seeds but sometimes insects also.^[5] Items are stored singly in various sites such as bark, dead leaves, clusters of conifer needles, or knotholes. Memory for the location of caches can last up to 28 days.^[6] Within the first 24 h the birds can even remember the relative quality of the stored items.^[7]

At bird feeders, Black-capped Chickadees tolerate human approach to a much greater degree than other species. In fact, during the winter many individuals accustomed to human habitation will readily accept seed from a person's hand.

Chickadee at feeder.

Metabolism

On cold winter nights, these birds reduce their body temperature by up to 10–12 °C (from their normal temperature of about 42 °C) to conserve energy.^[8] Such a capacity for torpor is rare in birds (or at least, rarely studied). Other bird species capable of torpor include the Common Swift Apus apus, the Common Poor-will Phalaenoptilus nuttallii, the Lesser Nighthawk Chordeiles acutipennis, and various species of hummingbirds.

Behavior

These birds are permanent residents, but sometimes they move south within their range, and even outside of it, in the fall or winter.

During the fall migration and in winter, chickadees often flock together. Many other species of birds – including titmice, nuthatches, and warblers – can often be found foraging in these flocks. Mixed flocks stay together because the chickadees call out whenever they find a good source of food. This calling-out forms cohesion for the group, allowing the other birds to find food more efficiently. When flocking, Black-capped Chickadees soon establish a rigid social hierarchy. In such hierarchies, males usually rank over females, and old birds over juveniles.

Black-capped Chickadee sleep in thick vegetation or in cavities, usually singly, though there have been suggestions that they may occasionally roost clumped together.^[9] The sleeping posture is with the bill tucked under the scapular (shoulder) feathers.

This bird scratches its head with its foot over the wing. It can bathe in water, dew, or snow; Young chickadees have been observed dust-bathing.

Flight is slightly undulating with rapid wing beats. Flight speed is about 20 km/h (12.5 mph).^[10]

Vocalization

The vocalizations of the Black-capped Chickadee are highly complex.^[11] Thirteen distinct types of vocalizations have been classified, many of which are complex and can communicate different types of information. Chickadees' complex vocalizations are likely an evolutionary adaptation to their habitat: they live and feed in dense vegetation, and even when the flock is close together, individual birds tend to be out of each others' visual range.

Black-capped Chickadee, Iona Beach Regional Park

The song of the Black-capped is a simple, clear whistle of two notes, identical in rhythm, the first roughly a whole-step above the second^[12]. This is distinguished from the Carolina chickadee's four-note call fee-bee fee-bay; the lower notes are nearly identical but the higher fee notes are omitted, making the Black-capped song like bee bay.

	Black-capped Chickadee Some 'gargles', then a minute of singing.
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The males sing the song only in relative isolation from other chickadees (including their mates). In late summer, some young birds will sing only a single note. Both sexes sometimes make a faint version of the song, and this appears to be used when feeding young.

The most familiar call is the familiar chick-a-dee-dee-dee which gave this bird its name. This simple-sounding call is astonishingly complex. It has been observed to consist of up to four distinct units which can be arranged in different patterns to communicate information about threats from predators and coordination of group movement. Recent study of the call shows that the number of dees indicates the level of threat from nearby predators. In an analysis of over 5,000 alarm calls from chickadees, it was found that alarm calls triggered by small, dangerous raptors had a shorter interval between chick and dee and tended to have extra dees, usually averaging four instead of two. In one case, a warning call about a pygmy owl – a prime threat to chickadees – contained 23 dees.^[13] The Carolina Chickadee makes a similar call which is faster and higher-pitched.

There are a number of other calls and sounds that these Chickadees make, such as a gargle noise usually used by males to indicate a threat of attacking another male, often when feeding. This call is also used in sexual contexts. This noise is among the most complex of the calls, containing 2 to 9 of 14 distinct notes in one population that was studied.

Reproduction

The Black-capped Chickadee nests in a hole in a tree, 1–7 m above ground. The pair either excavate the hole together, or use a natural cavity, or sometimes an old woodpecker nest. This species will also nest in a nesting box. The nesting season is from late April through June. The nest is built by the female only. It consists of a base of coarse material such as moss or bark strips, and lining of finer material such as mammal hair. Eggs are white with fine dots of reddish brown concentrated at the larger end. On average, eggs are 1.52 cm x 1.22 cm. Clutch size is 6-8 eggs. Incubation lasts 11–14 days and is by the female only, who is fed by the male. Hatchlings are altricial, naked with their eyes closed. Nestlings are fed by both sexes but are brooded by the female only (at which time the male brings food to her, which she passes on to the young). Young leave the nest 12–16 days post-hatching. They will still be fed by the parents for several weeks but are capable of catching food on their own within a week after leaving the nest.

Black-capped Chickadees usually breed only once a year, but second broods are possible if the first one is lost. First breeding is at one year of age. Maximum recorded lifespan is twelve years.

Black-capped Chickadees may interbreed with Carolina Chickadees or Mountain Chickadees where their ranges overlap.

Concerns

In the states of Alaska and Washington, and in parts of western Canada, Black-capped Chickadees are among a number of bird species affected by an unknown agent that is causing beak deformities, which may cause stress for affected species by inhibiting feeding ability, mating, and grooming. Black-capped Chickadees were the first affected bird species, with reports of the deformity beginning in Alaska in the late 1990s, but more recently the deformity has been observed in close to 30 bird species in the affected areas.^[14]

References

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• BirdLife International (2004). Poecile atricapilla. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
• Del Hoyo, J., Elliot, A., & Christie D. (eds). (2007). Handbook of the Birds of the World. Volume 12: Picathartes to Tits and Chickadees. Lynx Edicions. ISBN 978-84-96553-42-2
• Smith, S. M. (1991): The black-capped Chickadee: Behavioural Ecology and Natural History. Cornell University Press. ISBN 0-8014-2382-1 (1991 reprint).
• Smith, S.M., 1993, Black-capped Chickadee. In The Birds of North America, no. 39 (A. Poole, P. Stettenheim and F. Gill, eds.) Philadelphia: The Academy of Natural Sciences.