When I first began birding many years ago, birds that didn't look exactly as they were portrayed in field guides where dismissed by me as being an expected species in an unusual plumage. It wasn't until digital photography became a popular tool for documenting that I really started to look at birds with care and then realized not all my sightings were of expected species.
Take the case of this unusual bird spotted in Concord, NH, on 21 December 2008. It was discovered and thoroughly photographed by Jason Pietrzak in a park near an open river in a mixed-species flock including Black-capped Chickadees, Tufted Titmouse, and nuthatches. Jason first thought this bird appeared to be an Eurasian Blue Tit x Tufted Titmouse. Based on banding data, Eurasian Blue Tit Cyanistes (Parus) caeruleus has been shown to normally migrate only a few miles from their breeding territories, although northern subspecies can be irruptive in some years (HBW, Vol.12). During irruptive years, Eurasian Blue Tits are said to be mostly first-year birds (HBW Vol. 12). What makes this so interesting (see photos) is Jason's bird is thought by some to by a hybrid Black-capped Chickadee x Tufted Titmouse, others think it is most likely an escaped captive Blue Tit mated with a local Tufted Titmouse, or more likely, a Blue Tit x Black-capped Chickadee producing this plumage (www.birdingonthe.net/mailinglists/FRID.html#1238140017).
Photos are courtesy of Jason Pietrzak.
Jason summarizes his observations: "I no longer believe the bird has any Tufted Titmouse in it. When I first saw the bird, it was in a mixed flock with titmice and chickadees, so, based on a quick glance, I assumed it was a juvenile titmouse. On second view, I though it could be explained as a cross between Tufted Titmouse and Blue Tit (BLTI), but now after more thought, I'm convinced the bird is a cross between BLTI and Black-capped Chickadee (BCCH). A simple explanation is: imagine the head of a BLTI mounted on the body of a BCCH. The shapes and sizes of both birds are similar. The blue crown and eyestripe are strongly reminiscent of BLTI and the faded nature of those features can be expected in a hybrid. You can also see a trace of a collar, a feature in BLTI. The nape color is greenish-gray shared by both spcies, but the wings and tail, particularly the white edges, are clearly suggestive of Black-capped Chickadee."
As a conclusion, study all plumage details in your field guides. In the field, evaluate all characters of every unusual-looking bird you see.
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