Most bird species are raised by adult birds of the same species and learn to identify with their own species from an early age. Occasionally, though, a bird of one species chooses a bird of another species for a mate. What causes such an identity crisis? Perhaps the bird imprinted on the wrong species at an early age because it heard the songs of another species at a nearby nest. Or perhaps two birds were unable to find suitable mates of their own species. With hundreds of species of birds nesting in most regions of North America, it is not surprising that some individuals may occasionally have identity crises.

Hybridization, the mating of individuals of two different species, is rarely a smart strategy, however. If hybrid pairs produce offspring at all, those young birds may be sterile and often are less likely to survive and successfully find mates of their own. Nevertheless, hybridization is relatively common in some species groups (among Golden-winged and Blue-winged warblers, for example), and large hybrid zones may exist where the ranges of two species come together. For instance, Carolina and Black-capped chickadees hybridize where their ranges overlap in the parts of the east-central United States.

FeederWatcher Michele Musil of Sparwood, British Columbia, found a likely chickadee hybrid of another sort while photographing birds in her yard in November 2005.

Michele routinely has both Black-capped and Mountain chickadees at her feeders. Could the strange looking chickadee be a hybrid of the two? Michele wrote, “I have watched Black-capped and Mountain chickadees for years, and this is the first time that I have seen a chickadee that looks like this.” Michele took photos and reported her sighting to the Project FeederWatch staff at Bird Studies Canada. They consulted with Dick Cannings, the Christmas Bird Count coordinator for British Columbia, who said that such a hybrid would be rare—something he has never seen.

The researchers were able to observe the six resulting nestlings. At 18 days of age, the nestlings were almost identical to Black-capped Chickadees, but close examination revealed a very thin white eyebrow in three of the birds and white crescents above the ears of another two. Additionally, a few birds have been observed with thin white eyebrows or with crescents above or behind the eyes in the Rio Grande Valley of central New Mexico where Black-capped Chickadees, at the southwest edge of their range, are uncommon and Mountain Chickadees occasionally move down from nearby mountains.

Mountain and Black-capped chickadee ranges overlap broadly, but the birds typically occupy different habitats and different elevations during the breeding season. Researchers have found that although the two species have distinct vocalizations, individuals of one species occasionally respond to songs of the other species. According to the Mountain Chickadee profile in the Birds of North America series, DNA evidence indicates that Black-capped and Mountain chickadees are sister species. The close relationship is also indicated by their similarly complex social organization.**

The chickadees in Michele’s area migrate up and down in elevation. In the summer she rarely sees a chickadee of either species. The Mountain Chickadees are probably migrating further up in elevation than the Black-capped Chickadees during the breeding season. Perhaps a mixed pairing occurred at the edge of the two ranges.

Since Michele’s first report, she has seen a second possible hybrid. She suspected she had two for a while because one had a thin eyebrow while the other had a broader but fainter eyebrow. Then finally, on March 5, she saw both of the unusual-looking chickadees at once, confirming her suspicions. Michele wrote of the experience, “I am thrilled to have made such an exciting little discovery. I read exciting things about birds everywhere else not ever thinking that things would get exciting in my own backyard!” Without genetic analyses of the birds in Michele’s yard we will probably never know the true history of these unusual birds. However, Michele’s report highlights how interesting information can result from close examination of our common birds.

*Martin, Stephen G. and Kathy Anne Martin. 1996. Hybridization between a Mountain Chickadee and Black-capped Chickadee in Colorado. Colorado Field Journal, Vol. 30, No. 2, pp. 60-65.

**McCallum, D. A., R. Grundel, and D. L. Dahlsten. 1999. Mountain Chickadee (Poecile gambeli). In The Birds of North America, No. 453 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.