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Carolina Chickadee - Poecile carolinensis
Carolina Chickadee - Poecile carolinensis

[Image: 640px-Carolina_Chickadee1_by_Dan_Pancamo.jpg]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Paridae
Genus: Poecile
Species: Poecile carolinensis (Audubon, 1834)

The Carolina chickadee (Poecile carolinensis) is a small passerine bird in the tit family Paridae. It is often placed in the genus Parus with most other tits, but mtDNA cytochrome b sequence data and morphology suggest that separating Poecile more adequately expresses these birds' relationships (Gill et al., 2005). The American Ornithologists' Union has been treating Poecile as distinct genus since 1998.

Adults are 11.5–13 cm (4.5–5.1 in) long with a weight of 9–12 g (0.32–0.42 oz), and have a black cap and bib with white sides to the face. Their underparts are white with rusty brown on the flanks; their back is grey. They have a short dark bill, short wings and a moderately long tail. Very similar to the Black-capped Chickadee, the Carolina chickadee is distinguished by the slightly browner wing with the greater coverts brown (not whitish fringed) and the white fringing on the secondary feathers slightly less conspicuous; the tail is also slightly shorter and more square-ended.

The calls and song also differ subtly to an experienced ear: the Carolina chickadee's chick-a-dee call is faster and higher pitched than that of the Black-capped Chickadee, and the Carolina chickadee has a four note fee-bee-fee-bay song, whereas the Black-capped omits the high notes. Identification is very difficult even with an excellent view.

The most famous call is the familiar chick-a-dee-dee-dee which gave this bird its name and its song is fee-bee-fee-bay.

Carolina chickadees are so similar to Black-capped Chickadees that they themselves have trouble telling their species apart. Because of this they sometimes mate producing hybrids. The most obvious difference between the three chickadees is that the Carolina chickadee sings four-note song, Black-capped sing two-note songs, and the hybrids sing three-note songs.

Distribution and habitat
Their breeding habitat is mixed or deciduous woods in the United States from New Jersey west to southern Kansas and south to Florida and Texas; there is a gap in the range at high altitudes in the Appalachian Mountains where they are replaced by their otherwise more northern relative, the Black-capped Chickadee. They nest in a hole in a tree; the pair excavates the nest, using a natural cavity or sometimes an old woodpecker nest. They may interbreed with Black-capped Chickadees where the ranges overlap, which can make identification difficult.

[Image: Carolina_Chickadee-rangemap.png]

They are permanent residents, not usually moving south even in severe winter weather.

These birds hop along tree branches searching for insects, sometimes hanging upside down or hovering; they may make short flights to catch insects in the air. Insects form a large part of their diet, especially in summer; seeds and berries become important in winter. They sometimes hammer seeds on a tree or shrub to open them; they also will store seeds for later use.

During the fall migration and 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.

[Image: 640px-Carolinachickadeeonbranch.jpg]

Temperature regulation
Carolina chickadees are able to lower their body temperatures to induce an intentional state of hypothermia called torpor. They do this to conserve energy during extremely cold winters. In extremely cold weather conditions they look for cavities where they can hide in and spend up to fifteen hours at a time in torpor; during this time they are awake but unresponsive; they should not be picked up and handled at this time, as the stress of being held may cause their death.

Scent brings all the songbirds to the yard

by Lehigh University

[Image: scentbringsa.jpg]
"The sense of smell has been very understudied in birds, particularly songbirds, because they frequently have such impressive plumage and song variation," says Amber Rice, an evolutionary biologist at Lehigh University. "Some other recent work has documented that species of songbird can smell and prefer their species' odors, but this is the first example in currently hybridizing species that we know of." Credit: Lehigh University

Chickadees can smell! That is the news from a study out of Lehigh University, the first to document naturally hybridizing songbirds' preference for the scent of their own species.

Amber Rice, an evolutionary biologist at Lehigh, studies natural hybridization-when separate species come into contact and mate-to better understand how species originate and how existing species are maintained. The two species that make up the hybridized population she studies are the black-capped chickadee and its relative the Carolina chickadee.

Rice and Ph.D. student, Alex Van Huynh, set out to test the potential for scent to act as a mate choice cue, contributing to reproductive isolation between the black-capped and Carolina chickadees who live in the "hybrid zone" in the eastern Pennsylvania region where Lehigh is located.

Huynh and Rice found that both black-capped and Carolina chickadees produce chemically distinct natural oils. Testing both males and females of both chickadee species, they found that males and females prefer the smell of their own species over the smell of the opposite species. These preferences could be impacting hybridization. Their results have been published in an article entitled: "Conspecific olfactory preferences and interspecific divergence in odor cues in a chickadee hybrid zone" in Ecology and Evolution.

"The sense of smell has been very understudied in birds, particularly songbirds, because they frequently have such impressive plumage and song variation," says Rice. "Some other recent work has documented that species of songbird can smell and prefer their species' odors, but this is the first example in currently hybridizing species that we know of."

[Image: 1-scentbringsa.jpg]
Range map of the black-capped chickadee, Carolina chickadee, and approximate location of their hybridzone. Credit: Alex Van Huynh and Amber M. Rice

"Our results show that not only can odor cues be used by songbirds, potentially as a mate choice cue, but that they can have ecological and evolutionary consequences for songbird species," adds Huynh.

The black-capped and Carolina chickadees interbreed with one another, but their hybrid offspring suffer fitness costs. For example, the interbred chickadees are less likely to hatch from their eggs, and they have lower cognitive abilities than pure-species birds.

Interestingly, the researchers found that the chickadees they studied do not actively avoid the smell of the other species.

"This fact may be coincident with the observation that hybridization still does indeed take place," says Huynh. "We know the hybrid zone is very small and its width is stable over time. In other words, the geographic area of hybridization is not growing or shrinking."

[Image: 2-scentbringsa.jpg]
Y-maze odor preference chamber (left) and odor donor chambers (right). During preference tests, an opaque screen prevents birds in the Y?maze from seeing birds in the odor donor chambers. The odor donor chambers are kept in darkness during the preference trials to keep the odor donor birds still and silent. Perches are not shown in photo. Credit: Alex Van Huynh and Amber M. Rice

Birds of the same smell, tend to gel

Huynh and Rice caught wild birds from hybrid zone populations in Pennsylvania. They used gas-chromatography mass-spectrometry to analyze differences between the species in the natural oils the birds produce from their uropygial glands (also known as the preen glands). They tested for the species' odor preference using a Y-maze, measuring the amount of time a bird spends with a particular smell.

The experiments indicated a clear preference for same-species whole-body odors in both species of chickadees. These preferences were present in both male and female birds. The results, the team says, are consistent with a possible role for olfactory signaling in premating reproductive isolation in chickadees.

"Within the hybrid zone, the two species show differences in their uropygial oil chemistry as well as significant preferences for their own species over those of the other species," says Rice.

The team believes that researchers in the fields of animal behavior and chemical ecology will find their study particularly interesting. Investigating odor in future studies of songbird behavior such as mate choice, predation risk assessment, or competitive interactions, are some promising avenues for future inquiry.

Journal Reference:
Alex Van Huynh et al, Conspecific olfactory preferences and interspecific divergence in odor cues in a chickadee hybrid zone, Ecology and Evolution (2019). DOI: 10.1002/ece3.5497

Understanding how mating cues promote reproductive isolation upon secondary contact is important in describing the speciation process in animals. Divergent chemical cues have been shown to act in reproductive isolation across many animal taxa. However, such cues have been overlooked in avian speciation, particularly in passerines, in favor of more traditional signals such as song and plumage. Here, we aim to test the potential for odor to act as a mate choice cue, and therefore contribute to premating reproductive isolation between the black‐capped (Poecile atricapillus) and Carolina chickadee (P. carolinensis) in eastern Pennsylvania hybrid zone populations. Using gas chromatography–mass spectrometry, we document significant species differences in uropygial gland oil chemistry, especially in the ratio of ester to nonester compounds. We also show significant preferences for conspecific over heterospecific odor cues in wild chickadees using a Y‐maze design. Our results suggest that odor may be an overlooked but important mating cue in these chickadees, potentially promoting premating reproductive isolation. We further discuss several promising avenues for future research in songbird olfactory communication and speciation.
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