Alterus race Nelson’s Sparrow in CT

Nelson’s Sparrow (alterus), Hammonassett, CT, Nov 2011. Very bright and contrasting bird, note strength and color of facial triangle and contrasting back pattern. Flanks show well-defined streaking.

Nick Bonomo and I came across two Nelson’s-type sparrows at the west end of Hammonassett. One of the two gave nice looks and showed itself to be a quite bright and striking individual.

Subvirgatus, the Atlantic coast race, breeding in Maine and occurring here during fall and winter is the expected species, generally separated from the interior races, nelsoni and alterus by virtue of its rather drabber plumage and blurry-streaked flanks.

Nelson's Sparrow (subvirgatus), Milford Point, CT, winter 09. Note blurry flank streaking, lack of clear buff breast band and subdued facial 'triangle'.

Individual variation across the races, combined with a lack of knowledge of the status of the interior races compounds the identification issues of non-subvirgatus Nelson’s in CT.  Clearly this bird appears to be alterus/nelsoni rather than subvirgatus due to:

– clean, unmarked crown pattern

– intensity of the back pattern

– quite well-defined flank streaking

– brightness and clarity of the supercilium (with muted grey auriculars)

– underpart patterm showing a well-defined whitish belly and buffy breast band

Nelson's Sparrow (alterus), Hammonassett, CT, Nov. Same bird as above. Note underpart pattern consisting of a nice buff breast demarcated from white belly

Separating these two races can be tough, and being wary of trying to shoehorn each Nelson’s Sparrow into neat little boxes, the following features do seem to be good for alterus:

– broad gray crown stripe

– quite well-defined flank streaking

– very bright, clean orange facial triangle with ill-defined gray center

– white belly contrasting with streaked, buff breastband.

– upperparts quite contrasting with well-defined white “tramlines” (though lacking any blackish in the scaps shown by nelsoni)

 

Nelson's Sparrow (alterus), Hammonassett, CT, Nov. Note back pattern and broad, clean gray median stripe.

Nelson's Sparrow (subvirgatus), Milford Point, winter 09.

This synthesis was aided by a topical and educational article by Fletcher Smith, published in North American Birds, whose photo-essay showed an educational array of photos of the various races. See here: http://www.aba.org/nab/v65n2sparrows.pdf

Fletcher was kind enough to offer the following comments on this individual.

“Julian,
I agree that this bird is likely a nelsoni/alterus type bird rather than a subvirgatus for all the reasons you mention.  Subvirgatus (as you know) is a really dull looking bird, and this bird has a good bit of color to the face and pattern in the dorsum, along with black streaking in the cap. 

I think that nelsoni would have more black mottling in the cap, but the view here is not complete.  Alterus tends to have distinct streaking in cap, not mottling like nelsoni, and this bird looks like it has streaking not indistinct mottling.  The dorsum is also not strongly patterned and has no dark centers suggesting alterus not nelsoni.  The cheek patch looks like it is mostly gray, not infused with ochre color.  This is typical of alterus.  I tend to lean alterus on this bird, I see no characters that suggest nelsoni at all. 

Very little is known of the migratory routes of these birds, and my hope is that the article I wrote will push subspecies ID to the forefront on these birds and allow for a more complete knowledge of the migration routes. “

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