Monday, October 10, 2011

Quiz #420 (2011-4-02) Solution

Click on picture(s) for a larger view.

Solution by Tony Leukering

All of this week's respondents arrowed to the correct genus, with the lion's share of those selecting the correct species. The genus Chordeiles is a small one (only three species), all of which occur in the ABA area, but with most of that area being visited by only one. Or none. Identification of nighthawks is quite difficult, particularly for perched birds. In fall, accurate ID often requires first ageing the bird in question, as variation in plumage across the broad range of Common Nighthawk can swamp the differences between species, so eliminating some of that variation by determining the bird's age is most useful. With this week's quiz bird, we are in luck, as the bird is not only readily aged, but sexed, too.

As noted by a number of respondents, our quiz bird is an adult male, determined so by the distinct and fairly wide white subterminal band on the tail. So, we don't have to deal with the multiplicity of juvenal plumages. However, in some instances, it might have been better -- or, at least, easier, had the bird been a female, because that wide and bright white primary patch would have eliminated both Lesser and Antillean from consideration. But, alas, because it's a male, all three species are still in the possible solution set.

Returning our gaze to the primaries, that white patch on the primaries looks to be too proximal to be that of the patch of a Lesser Nighthawk, but the angle at which we gaze might make that assessment a bit problematic. However, looking at the other end of the primaries, we can see that the wingtips extend well beyond the tail tip, confirming our excision of Lesser Nighthawk from the solution set; Lesser's wingtips just barely reach past the tail tip, even in adult males (which have longer, more pointed wingtips than do females; juveniles have even shorter wingtips -- in all species). The bright white underparts provide the third and final nail in the coffin of Lesser Nighthawk as a possibility.

Antillean Nighthawk is even more similar to Common than is Lesser; the two were even considered conspecific for a while. The two species share a wide and more-basal primary patch, but Antillean shares the buffy underparts of Lesser and adult males sport a narrower subterminal tail band than shown by our quiz bird. I took this picture of an adult male Common Nighthawk south of Midway, Baca Co., CO, on 30 May 2011.

One respondent's answer neglected capitalization, so was precluded from being correct for the competition.

Incorrect species provided as answers:
Antillean Nighthawk - 1
Lesser Nighthawk - 1

Congratulations to the 24 of 26 getting the quiz correct:
Tyler Bell
Thomas Hall
Su Snyder
Nick Komar
Kirk Huffstater
Pam Myers
Patty McKelvey
Jennifer Courtemanche
Rudi Nuissl
Josh Parks
Margie Joy
Al Guarente
Liston Rice
Devich Farbotnik
Bruce Cyganowski
Diane Porter
Richard Jeffers
Ted Cooper
Peter Wilkinson
Marcel Such
Margaret Smith
Bryan Guarente
Chishun Kwong
Joel Such

Answer: Common Nighthawk