The black-capped chickadee (Poecile atricapillus) is a small, nonmigratory, North American passerine bird that lives in deciduous and mixed forests. It is a member of the Paridae family, also known as tits. It has a distinct black cap on its head, a black bib underneath, and white cheeks. It has a white belly, buff sides, and grey wings, back, and tail. The bird is well known for its vocalizations, including its fee-bee song and its chick-a-dee-dee-dee call, from which it derives its name.
The black-capped chickadee is widely distributed throughout North America, ranging from the northern United States to southern Canada and all the way up to Alaska and Yukon. It feeds primarily on insects and seeds, and is known for its ability to cache food for use during the winter. The hippocampus of the black-capped chickadee grows during the caching season, which is believed to help it better remember its cache locations. The black-capped chickadee is a social bird and forms strict dominance hierarchies within its flock. During the winter, these flocks include other bird species. It has the ability to lower its body temperature during cold winter nights, allowing it to conserve energy.
Black-capped chickadees build nests in tree cavities, with the nesting season starting in late April and lasting until late June. They lay on average 6–8 eggs, which hatch after 11–14 days. Juveniles fledge 12–16 days after hatching.
The population of black-capped chickadees is thought to be increasing, and they are considered a species of least concern by the International Union for Conservation of Nature (IUCN). It is the state bird of both Massachusetts and Maine in the United States, and the provincial bird of New Brunswick in Canada.
Taxonomy In 1760, French zoologist Mathurin Jacques Brisson included a description of the black-capped chickadee in his book based on a specimen collected in Canada. He used the French name and the Latin Parus Canadensis Atricapillus. The two stars (**) at the start of the section indicates that Brisson based his description on the examination of a specimen. Although Brisson gave it Latin names, these do not conform to the binomial system and are not recognized by the International Commission on Zoological Nomenclature. In 1766, Swedish naturalist Carl Linnaeus published the 12th edition of his Systema Naturae, which included 240 species that had been previously described by Brisson. One of these was the black-capped chickadee. Linnaeus included a brief description, coined the binomial name Parus atricapillus and cited Brisson's work. The specific epithet atricapillus is Latin for "black-haired" from (black) and (hair of the head).
Though originally placed in the genus Parus with most other tits, mtDNA cytochrome b sequence data and morphology suggested that separating Poecile more adequately expressed these birds' relationships. The genus Poecile had been introduced by German naturalist Johann Jakob Kaup in 1829, and the American Ornithologists' Union moved the black-capped chickadee into this genus in 1998. Molecular phylogenetic studies have shown that the black-capped chickadee is sister to the mountain chickadee (Poecile gambeli).
The following cladogram shows the relationships between the various chickadee species, a subset of genus Poecile:
Until the late 1900s, the black-capped chickadee was considered by some to be conspecific with the willow tit of Eurasia and the Carolina chickadee, due to their very similar appearance. A 1989 study demonstrated that the Willow tit and black-capped chickadee were different species; however, the distinction of the Carolina chickadee remained in question until 2005.
Subspecies Nine subspecies are currently recognized. They are presented below in the taxonomic order set by the International Ornithologists' Union (IOC) Poecile atricapillus turneri (Ridgway, 1884): Found in southern Alaska and northwest Canada and has the palest colouring of all subspecies. Poecile atricapillus occidentalis (Baird, 1858): Ranges from southwest British Columbia to northwest California, and is the smallest in size and darkest in colouring of all subspecies. Poecile atricapillus fortuitus (Dawson, 1909): Ranges from inland southwest Canada to northwest U.S., and is notably buffier than other subspecies. Poecile atricapillus septentrionalis (Harris, 1846): Ranges from western and central Canada to southern U.S. It is visually similar to P. a. atricapillus but has slightly longer wings and tail. Poecile atricapillus bartletti (Alrich & Nutt, 1939): Lives only in Newfoundland, Canada, and is the only species with different mtDNA, likely due to geographic isolation. It is larger and darker than P. a. atricapillus. Poecile atricapillus atricapillus (Linnaeus, 1766): Nominate subspecies, which ranges from eastern and central Canada to northeastern U.S. Poecile atricapillus garrinus (Behle, 1951): Lives in western central U.S. It has a brown back and buff rump. Poecile atricapillus nevadensis (Linsdale, 1938): Lives in western U.S., and is visually similar to P. a. septentrionalis but with paler edges to the wings and tail. Poecile atricapillus practicus (Oberholser, 1937): Lives in the Appalachian Mountains in the eastern U.S. Similar to P. a. atricapillus, although slightly smaller, less dark on the back, and less prominent white edge to the wings and tail.
Description
The black-capped chickadee has a black cap and "bib" with white cheeks. Its underparts are white with buff-coloured flanks. Its back is unstreaked and greenish grey, and the tail and wings are slate grey. It has a black beak and legs, and dark brown irises. Males and females are generally similar, although males have a larger bib. They can also be distinguished based on a combination of weight and tail length. Tarsus length does not significantly differentiate sexes. Males have a wing length of , a tail length of , a bill length of , and a tarsus length of . Females are on average slightly smaller, with a wing length of , a tail length of , a bill length of , and a tarsus length of . Both sexes weigh . Juveniles are visually similar to adults but with fluffier plumage.
Although range can generally be used to separate them, the black-capped chickadee is very similar in appearance to the Carolina chickadee. The edges of the wings are somewhat paler than the Carolina chickadee, and the bib of the black-capped chickadee has a "messier" border than the Carolina chickadee. The most reliable way to distinguish the two species is by vocalizations. Black-capped chickadees have a slower, hoarser, two-part song, whereas Carolina chickadees have a three-part song.
Black-capped chickadees are also somewhat similar to mountain chickadees and boreal chickadees. Mountain chickadees can be distinguished by a distinct white stripe above their eyes, and boreal chickadees have a brown cap as opposed to the black cap of the black-capped chickadee.
Vocalization
The vocalizations of the black-capped chickadee are highly complex, with 16 distinct types of vocalizations being used to convey an array of information. These 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 other's visual range.
One of the most recognizable sounds produced, particularly by the males, is the two-note fee-bee song. It is a simple, clear whistle of two notes, identical in rhythm, the first roughly a whole-step above the second. The frequency of their songs typically starts around 400 Hz, and various tones spanning roughly 1 kHz are sung within the song. A decrease of roughly 200 Hz occurs when the first note (fee) is sung, and then another decrease around 400 Hz takes place between the end of fee and the beginning of bee. In spite of these multiple changes in frequency, though, anybody listening to the song only hears a pure, high-frequency tone. 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. The males sing the song only in relative isolation from other chickadees (including their mates). In late summer, some young birds sing only a single note.
Both sexes sometimes make a faint version of the fee-bee song, and this appears to be used when feeding young. During breeding, the male may make this call to attempt to attract a female. During nesting, this call is used by both sexes to call to their partner when not in sight. Distinguishing males and females based solely on their singing is difficult. A bioacoustic analysis performed on both male and female songs revealed that male fee-bee singing fluctuates more, and the absolute amplitude of both sexes is the same.
The most familiar call is the chick-a-dee-dee-dee, which gave this bird its name. This simple-sounding call is astonishingly complex. Scientists have been studying it since the mid-1970s. It is produced by both males and females year-round. It has been observed to consist of up to four distinct units—referred to as A, B, C, and D. A, B, and C are variations of the "chick-a" part of the call, and D is the repeated "dee". These can be arranged in different patterns to communicate information about threats from predators and coordination of group movement. These four notes only ever appear in this consecutive order with each preceding note blending into the next; however, not all four notes always appear in the call. Like other sounds the chickadee produces, it may be heard in multiple variations. The A and B notes are almost identical to one another in both frequency and duration, though black-capped chickadees possess the ability to quickly notice the difference between these two notes. No such similarity is seen between the C and D notes. The C note fluctuates from low to high then back to low, whereas the D note has a constant frequency. While not confirmed, one study found evidence of a function behind the C and D notes: the C note is used indicate the location of food, and the D note is used to distinguish between a member of the same species and a potential predator.
Neither individual notes nor groups of notes have an equal probability of appearing in the chick-a-dee-dee-dee song. Its syntax form may take on several different structures, but the two most commonly heard are [A][D] and [B][C][D]. Calls containing the D note are most frequently heard. A study of the call showed that the number of dees indicates the level of threat from nearby predators. In an analysis of over 5,000 alarm calls from chickadees, alarm calls triggered by small, dangerous raptors had a shorter interval between chick and dee and tended to have extra dees, typically four instead of two. In one case, a warning call about a pygmy owl—a prime threat to chickadees—contained 23 dees. The Carolina chickadee makes a similar call, which is faster and higher-pitched.
Other species have also been observed making use of these chick-a-dee-dee-dee alarm calls. During the non-breeding season, mixed species flocks may form to help with foraging and predator avoidance, and may include nuthatches, woodpeckers, kinglets, and vireos among others. These species will react when a chickadee makes the alarm call. Red-breasted nuthatch have even been observed reacting more strongly to higher-threat alarm calls, indicating some understanding of their syntax.