David Sibley is at it again, helping birders understand and identify subspecies of North American birds. http://www.sibleyguides.com/2011/03/about-the-list-of-field-identifiable-subspecies/
After using eBird for a while, and dicovering that you can submit sightings of birds below the species, level, I’ve been fascinated by looking closer at birds and variations in plumage. Here in Albuquerque we have Interior Bushtits, Eastern Curve-billed Thrashers, and Woodhouse’s Western Scrub-Jays, not to mention the various wintering forms of Dark-eyed Juncos: Oregon, Pink-sided, Gray-headed, and Cassiar Slate-colored. We probably have three populations of Hermit Thrushes wintering here but these are hard to distinguish (although Sibley states that “most individuals should be relatively easy to classify”–just means I need to look closer and get a decent camera to record birds!).
I’ve been meaning to make a list like this including the relevant science and range maps behind it all. Based on Sibley’s posts on Mountain Chickadees and White-throated Sparrows, I’d say he’s well on his way to doing just this. I’d better get cracking.