Widespread in the northern United States and Canada, the Black-capped Chickadee is a familiar backyard bird for millions of people. Over most of its range, it’s among the easiest birds to identify, but in a few areas, it’s among the most challenging.
Most of the seven chickadee species in North America are easy to distinguish. But Carolina Chickadee is extremely similar to Black-capped, and their ranges meet along a boundary that stretches from the Atlantic Coast to the Great Plains.
Carolina Chickadees average smaller than Black-cappeds. However, both species vary regionally and individually in size; the smallest Carolinas occur in the southern part of their range, so size has only limited value for ID where the two species come together. Black-capped also tends to look a little longer-tailed and larger-headed than Carolina.
Their voices differ. Black-capped Chickadee sings two or three syllables: see-beeeor see-bee-ee, with the first note higher. Carolina Chickadee sings four syllables, the first and third very high-pitched: see-bee-see-bay. The callnotes,chick-a-dee-dee-dee, tend to be faster and higher as given by the Carolina, but they’re variable in both species.
When the birds are in fresh plumage (fall and winter), wing pattern is the most visible difference. The greater coverts have distinctly paler broad edges on Black-capped, creating a pale panel on the wing and connecting to the whitish edges of the tertials and secondaries. The effect is of a whitish “hockey stick” on the dark gray wing. On Carolina Chickadee, the greater coverts are essentially the same gray as the back and the tertial edges are not as pale as on the Black-capped. These differences become obscure by late spring, when adults of both species are in worn, drab plumage.
In addition to wing pattern, the Black-capped tends to be a more colorful bird. It shows an olive tinge on the back, where the Carolina is simply gray. The wash of buff on the flanks is usually stronger on the Black-capped. The white cheeks often look brighter white on the Black-capped, and extend farther back, to the edge of the nape. On Carolinas, the white cheeks may fade to pale gray toward the rear. All these differences are subtle, but in combination, they can make a Black-capped seem noticeably brighter when it’s surrounded by Carolina Chickadees.
During some years, big autumn flights of Black-cappeds are noted in eastern Canada and the northern states. These movements don’t extend very far south, but they often result in some individuals showing up a little south of the normal range. Birders near the northern edge of Carolina Chickadee territory should watch for a slightly larger, more colorful outlander to join their local chickadee flock in winter.
The range boundary between Black-capped and Carolina is marked by a zone in which most chickadees are hybrids. If you’re in that zone, you may get to witness remarkable changes over time; see the sidebar below.
What to look for
Size and shape. Slightly larger, bigger-headed, and longer-tailed than Carolina Chickadee.
Overall colors. Mostly gray, black, and white, but with tinges of olive on back and buff on flanks in fresh plumage.
Greater coverts. These wing feathers have broad, pale edges, paler than the back. Obvious in fresh plumage of fall and winter, becoming faded and worn by late spring.
Flight feathers. Dark tertials, secondaries, and tail feathers have noticeable white edges when fresh.
Face pattern. Bright white cheek patch extends back to edge of nape.
This bird’s posture may exaggerate the extent of the white cheek patch, but the brightness of the patch is no illusion. This fresh-plumaged winter bird shows the subtle-but-classic field marks that separate Black-capped Chickadee from its Carolina cousin, including an olive tinge on the gray back and warmer buff on the flanks. In particular, note the wing pattern, with broad pale edges on the greater coverts and white edging on the tertials and other flight feathers. Irruptive flights during some fall seasons bring a few Black-cappeds to areas south of the breeding range in winter. It’s worth watching for such strays among Carolina Chickadees at a bird feeder, where individuals can be studied closely.
Carolina Chickadees molt in summer, so this September bird is in very fresh plumage. Even so, it shows little contrast in the wing pattern. The edges of the tertials and secondaries are only a bit paler than the rest of the feathers, and the greater coverts are simply medium gray. On a Black-capped in fresh plumage, whitish edges to these feathers create a noticeable pattern. This bird is also less colorful overall than the Black-capped, with a plain gray back lacking olive tones, only a slight buff wash on the flanks, and less extensive white on the cheeks. Carolinas also average slightly smaller and shorter-tailed than Black-cappeds. All these differences are subtle and hard to see in the field.
The feathers on this Mountain Chickadee look drab and worn by comparison to the Black-capped and Carolina Chickadees on the previous page. That’s just the result of the season; all adult chickadees start to look ragged by summer, when all their feathers are many months old. When a Mountain Chickadee has molted and is in fresh plumage (fall and winter), the white eyebrow stripe is strikingly obvious, making the bird easy to identify. On a bird with worn plumage, this stripe (made up of white feather tips) can be almost completely worn away. Black-capped and Mountain Chickadees overlap in some parts of the West and have even been known to interbreed, so their ID can be tricky at times.
Widespread in the mountains of Mexico, this chickadee enters the United States only in the Chiricahua Mountains of southeastern Arizona and the Animas Mountains of southwestern New Mexico. It’s easily recognized by range, as no other chickadees occur in those mountains. Superficially it looks like the Black-capped, but a closer look shows that the Mexican Chickadee has a much more extensive black bib, extending down onto the chest, and a dark gray wash along the sides and flanks. This was among the last bird species in the lower 48 states to reveal its nesting secrets; no ornithologist saw the nest and eggs of the Mexican Chickadee until Herbert Brandt looked into a nest in 1948.
A shifting frontier
Two chickadee species meet along a line stretching from New Jersey west to Kansas: Black-cappeds north of the line and Carolinas south of it. Where they meet, they interbreed, so the “pure” forms of the species are separated by a hybrid zone about 20 miles across.
The fact that they interbreed doesn’t mean they’re the same species. The hybrids have lower breeding success and lower chances of survival than either of the parent species. So the hybrid zone stays narrow and acts as a kind of isolating mechanism.
This hybrid zone has been gradually moving north. Historical information is sketchy and mostly unreliable, but we know that in Ohio, for example, a northward spread of Carolina Chickadee was apparent as long ago as the 1930s. More recently, very careful studies in eastern Pennsylvania have found that the hybrid zone is moving north at a rate of about 7 miles every 10 years. At its northern edge, the chickadee population may shift from Black-cappeds to hybrids to Carolinas in the span of about three decades.
The shift is tied to a changing climate. Black-capped Chickadees are more cold-hardy than Carolinas. As average winter temperatures gradually rise, Carolina Chickadees are able to survive the winters farther north. Researchers in the Pennsylvania study found that changes in temperature tracked closely with the northward movement of the chickadee hybrid zone.