08 March 2011

Possible Dark-eyed Junco x Song Sparrow Hybrid

This afternoon I photographed an interesting DARK-EYED JUNCO in my yard in Logan, Cache County, Utah. The bird had most of the basic traits of a female Oregon subspecies Dark-eyed Junco, except for a few anomalies. Most obvious was a soft-edged buffy malar ("mustache") stripe that matched the flanks in color. I grabbed a few quick photographs through the window, but could not relocate the bird when I went outside to try for better photos. In the photographs, I noticed that the bird also has a hint of a pale supercilium ("eyebrow"), a slightly more striped back than expected (although perhaps not entirely outside the range of variation for a pure DEJU), and the white in the outer tail feathers appears to not reach the tip of the tail, instead fading to black.

The combination of anomalous traits make me think this is not just an aberration, but more likely a hybrid of some kind. Hybrids between DEJU and sparrows of the Zonotrichia and Melospiza genera have been previously reported. It seems to me like the best match for this bird would be a Dark-eyed Junco x Song Sparrow hybrid, a combination which has been reported before. (For example, here is a link to a possible photo of another DEJU x SOSP hybrid, and here is a link to an article describing another.) It is my opinion that the only way to be 100% certain of any hybrid parentage is with genetics, but I think this is the most likely explanation for this bird based on the traits observed, the frequency and range overlap between the species in question, and the fact that hybridization between these two has been documented previously. The Song Sparrow-like traits are pretty weak on this bird, so a backcross (the offspring of a mating between a pure DEJU and a DEJU x SOSP hybrid) also may be likely. Any thoughts or comments on this bird are welcome.

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