La Jolla oystercatcher "scoring": American or hybrid??


lehman.paul@verizon.net
 

Based on the fine extensive series of photos taken of today's (9 July) oystercatcher at La Jolla by Dean Budd, Jonathan Casanova, John Dumlao, Mandy Etpison, and Barbara Wise, among others, it is possible to apply the "Jehl scale" with some reasonable degree of accuracy. Curtis Marantz is the first person to take the bait, and his comment are below. If a few other folks would like to do the same, please do! And if you don't have access to any of these sets of photos (see eBird), let me know, offline. FWIW, I think the uppertail coverts are clearly MOSTLY dark.

--Paul Lehman, San Diego

Curtis writes:

It is right on the edge of "good enough," given that I reach 29-30 when I score it with the details below.

It really comes down to whether you think the uppertail coverts are closer to "nearly equally black and white," or instead, mostly black with some white.  If you think there is less than 50% white there, it won't reach the magical number of 30, and I do not see it as being 50% white.  In my experience, a quick rule of thumb is that unless the uppertail coverts are at least 50% white and the undertail coverts are almost entirely white, it won't reach the score you need.  These characters are correlated, so birds that have problems with one or two tend to have problems with the rest.  This said, the vast majority have white bellies, white thighs, and pretty good wing-stripes, so the intermediate birds tend to look far more like American Oystercatchers than Black Oystercatchers, and I see very few that have mostly black underparts with only limited white.

uppertail coverts - 1-2 (to me it is between "black with a few white mottlings" and "nearly equally black and white"; I would have said ¾ black and ¼ white, so maybe best rated at 1½?)
tail - 1 (mainly black, trace of white at base of vanes)
chest - 3 (black chest band bordered by ragged edge on upper breast)
belly - 6 (entirely white, as in palliatus)
undertail - 3 (mainly white)
thighs - 4 (entirely white, as in palliatus)
greater coverts - 3 (6-15 mm, but hard to know for sure unless you can measure it in-hand!)
extent of wing stripe - 1 (white markings confined to inner half of secondaries - actually I have a hard time seeing any white in the secondaries, so maybe more like ½?)
underwing coverts - 3 (mainly white)
axillars - 4 (white, as in palliatus)