Song sparrows - a new view


My last blog on song sparrows was almost 4 years ago (variations in song sparrows).  I wrote it about variations in song sparrows over a large area.  I am redoing the blog because I have more additions to the photos - from four different locations in the northwestern quadrant of North America.  

Apparently, there are some 24 subspecies of song sparrow in North America.  Continental variants tend to be more lightly coloured, as you can see from the Kelowna and Lloydminster birds I photographed above.  Coastal variants tend to be more darkly shaded, as you can see by the Nanaimo and Alaska subspecies.  

Not only does the feathering differ in the subspecies, the songs vary regionally as well.  They seem to have commonalities in that their songs are divided into 3 or 4 parts, often starting out with a pair of chirps followed by a series of notes, a warbling rattle, and possibly a soft finish.  You can listen to four different songs by clicking here.

This begs the question, "Why are there so many subspecies?"

There are several factors.  First of all, the species inhabits almost all of North America, with the exception of the extreme north in Canada and eastern Alaska.  The species has acclimated to local conditions and the combination of radiation and selection has caused shifts in the local gene pools.  Northern species do migrate south; those in Alaska may travel as far south as Mexico.  However, they don't breed there as a rule and travel north again to their familiar ranges in spring.  This tends to keep local populations isolated from those far afield.

There is some mixed breeding between subspecies that occurs due to range overlap or because migrating birds stay for the breeding season instead of travelling back to their home region.  This interplay of subspecies helps to maintain species-specific characteristics, and I don't expect any one subspecies to become a different species anytime soon.

Another interesting difference is size; Aleutian songsparrow subspecies may be three times larger than their California counterparts.  I expect that the larger birds are better adapted for colder climates; larger individuals have a better chance of surviving than smaller ones.

Thanks for reading.

Eric Svendsen     www.ericspix.com

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