Earlier this winter, I commented on what I thought was a case of misplace migrants when I saw a juvenile Yellow-bellied Sapsucker in my Minnesota backyard. Similarly, among the bevy of birds that crowded into the feeders in the past couple of days was an unusual one — unusual to see at this time of year at any rate.
It turns out the confusion over which species of sparrow one is seeing in the winter is not uncommon — for two reasons: first, among northern-breeding bird species, some juvenile and even adult birds apparently do not always migrate (which might be a fatal mistake); second, some birds find the opposite sex of a different species more attractive than their own, and produce hybrid offspring that share some of both parents’ characteristics. So what is going on here with this supposed Chipping Sparrow?
Tree Sparrows and Chipping Sparrows are two of the seven species of Spizella in North America. But…The two species are not supposed to be found in the same places in winter. So is this a case of failure to migrate? Has this bird been here all winter, toughing out the frigid conditions when it could be basking in the warmth of Floridian sunshine?
The two species do look similar, except for a definite chestnut streak behind the eye in Tree Sparrows and a black one in Chipping Sparrows. Tree Sparrows are somewhat bigger in body mass, although not necessarily longer in head to tail length and possess a definite central black breast spot.
Tree Sparrows have a bi-colored bill, yellow lower with gray/black upper parts. Breeding adult Chipping Sparrows have a solid black bill. Is my backyard visitor some kind of hybrid, with its bi-colored bill and faint central breast spot?
Well, it turns out that Chipping Sparrows only show the solid black bill during the breeding season, and it is, in fact bi-colored during the non-breeding season. In addition, Chipping Sparrow breast plumage is somewhat variable, and some individuals do show black spotting. So I assume this is not a hybrid product of cross-species interactions, but is in fact, a misplaced migrant (or it failed to migrate).
Which just leads me to wonder why, if migratory species can, in fact, survive harsh winters like this, why do they bother to migrate where they have to crowd in with the already established resident birds? Do all the backyard bird feeders enable seed-feeding birds to remain in their breeding areas all year? Is this an example of the effect of climate change (hard to think of warming in the middle of a Minnesota winter!) on bird distributions?