Tuesday, November 1, 2011

"Interior" Nelson's Sparrow - alterus or nelsoni?

UPDATE 11/3 - Julian has made a blog posting with his photos and thoughts on this bird, so check it out. Included are thoughts from Fletcher Smith, author of the recent NAB article on the sharp-tailed sparrows, who agrees this bird fits alterus best.

ORIGINAL POST: Yesterday at Hammonasset Beach State Park in Madison, CT Julian Hough and I observed this bright Nelson's Sparrow, clearly representing one of the interior races. It is quite unlike the drab, gray-toned Acadian subvirgatus subspecies that breeds not far up the Atlantic coast to our north. All photos are untouched - only cropped.




















Nelson's Sparrow, likely alterus

Separating alterus from nelsoni during migration is a difficult task. A recent article in North American Birds states that approximately 30% of interior birds banded in Virginia during the nonbreeding season could not be assigned to subspecies given current knowledge. If they're tough in the hand, they're tougher in the field.

Here are some notes:
- high-contrast facial pattern with bright orange triangle and gray auricular
- clean orange supercilium without internal markings
- broad, clean gray central crown stripe, generally lacking internal markings
- white braces down the back bordered by brown (not black)
- wing coverts edged with warm brown that look rufous-toned in some shots
- yellow-ochre flanks and breast band filled with bold brown streaking...weakest at the central breast, boldest and brownest down the flanks
- contrasting white belly
- whitish throat that has a hint of pale yellow-ochre color to it

I am not sure that this bird, from these photographs, can be certainly assigned to either interior subspecies. But, some plumage features seem to indicate alterus over nelsoni (namely the back pattern and broad, unmarked central crown stripe). Based on geography, alterus is more likely to occur here than nelsoni. The bird's plumage seems to fall within the range of what alterus is capable of, perhaps even flank streaking so bold. The latest photo spread in NAB illustrates a few alterus every bit as bright as this one. If anyone has differing thoughts, please let me know!

- Nick

1 comment:

  1. A beautiful sparrow for sure! I've yet to see one of those.

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