Monday, November 14, 2011
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Solution by Tony Leukering
This week's quiz bird resulted in answers citing six species of blackbird. In blackbirds, eye color is useful, so we'll start there. Our bird's dark eye should rule out most Boat-tailed and Great-tailed grackles (except for females of some Gulf of Mexico populations of the former) and adult Common Grackles and Bronzed Cowbirds. Granted, that leaves a lot still in the possible solution set, but we can narrow things down from here. Knowing our bird's age would help tremendously, but ageing many blackbird species in the field is quite difficult, if not impossible, as they generally conduct extensive preformative molts, thus immatures are very similar in most respects to adults.
The streaky blackbirds (Red-winged, Tawny-shouldered, and Tricolored) are eliminated by the lack of streaks; any individual of the two species that isn't obviously blackish would have streaks. Common Grackle never shows such pale head and underparts, particularly the former, and because of the latter, it does not show the contrasting dark feather centers of the underparts of our quiz bird. Brown-headed Cowbird can be ruled out by our bird's lack of contrastingly pale throat bordered by dark lateral throat stripes. Female Shiny Cowbird is never this cold-colored gray-brown and the bird is not a juvenile Shiny because it lacks streaks and wingbars. Our quiz bird is not a Bronzed Cowbird, as that species never shows even this prominent of a pale superciliary, particularly in front of the eye. Additionally, that species has a deeper and shorter bill than sported by the quiz bird. The large-tailed grackle species are just that, large-tailed, which our quiz bird is not.
That leaves us with the Euphagus problem. Though field guides may make Rusty and Brewer's blackbirds seem relatively simple to separate, the two are often quite similar, with some individuals probably best left unidentified. However, this bird is not one of those. Even the dullest and youngest of Rusty Blackbirds would show a much more obvious superciliary, while only the very youngest would still show a dark eye, but should not upon completion of its preformative molt (which is true of this bird). Additionally, female Rusty Blackbirds show auriculars more sharply-defined as a patch by rear and lower borders that our bird lacks. Finally, the bill's depth is a good indicator of Brewer's Blackbird, but, perhaps, not definitive. However, something not shown in field guides is the distinctive upright-and-head back strutting of Brewer's Blackbird that I find very useful in identifying the species, even separating it from Rusty Blackbird. Our quiz bird illustrates that behavior as well as any static picture can.
Peter Wilkinson tops the leader board with a perfect 7-for-7 score in this quarter's competition, with Al Guarente and Thomas Hall being one correct answer behind. As for the yearly competition, two Californians -- Robert McNab and Pam Myers -- lead with 35 correct responses, with Marcel Such and Peter Wilkinson right on their heels with 34 correct, and Bryan Guarente two back at 33.
Incorrect species provided as answers:
Bronzed Cowbird - 1
Shiny Cowbird - 2
Common Grackle - 1
Brown-headed Cowbird - 1
Rusty Blackbird - 2
Congratulations to the 14 of 21 getting the quiz correct:
Answer: Brewer's Blackbird