Posted by Dennis Paulson (220.127.116.11) on September 03, 2002 at 14:07:28:
In Reply to: Never enough dowitchers posted by Matthew Kenne on August 11, 2002 at 15:52:37:
Matthew Kenne wrote:
The molt schedule is another clue that is garbled to me. I'm assuming San Diego is a normal wintering area for both dowitchers, so Short-billed could/should be in the middle of molting to basic plumage (according to Dunn's statements), and Long-billed could/should have completed its molt before arrival. Point for Short-billed. I turned to Shorebirds of the Pacific Northwest, by Dennis Paulson, for fall molt help and found these conflicting statements: under Short-billed- "Adults begin body molt soon after arrival, underparts showing more and more white and then upperparts more and more gray. In northern part of region body molt essentially complete in some individulas by mid August." But under Long-billed: "Adult Long-billed may molt more rapidly than Short-billed in fall and typically look gray-headed (more so than Short-billed) while passing through the Northwest. Molt into non-breeding plumage begins in late August, and by late September many adult Long-billed in virtually complete nonbreeding plumage." How can Paulson's description of body molt in non-wintering areas be so opposed to Dunn's? If this molt-timing argument is limited to primary flight feathers, with LB in active molt on migration while SB isn't, we're up the creek with this photo.
Joe Morlan asked me to look at some dowitcher photos, and while doing so, I read comments by others about them. I wanted to try to clarify the stuff I wrote in my shorebird book that you found confusing.
I wrote that LBDO molted more rapidly than SBDO, which might be confusing if one looks at it from the San Diego perspective. From my research, LBDO body molt took about a month (late Aug to late Sep), while SBDO body molt took about a month and a half (early Jul to mid Aug). This was based on examination of specimens, supplemented by looking at them in the field. I'll stand behind my statement that SBDOs molt their body feathers while in migration through the Northwest, as they are already flecked with gray above and white below when they arrive here in July. I don't have Jon Dunn's statements about their molt here to contrast with mine (you said my statements were "so opposed to Dunn's"), but I think my statements are at least internally consistent. The reason LBDO might arrive in San Diego in full basic plumage is that they take a lot longer to proceed south through the continent, as they also molt their wings (and tail?) on the way. Thus SBDO would arrive in San Diego in molt, LBDO after molt. I don't think there's anything in my book that would contradict that.
I do agree that I could have been clearer in distinguishing the molting patterns of the two species! Especially the part about LBDO looking more gray-headed, even though I had already said that molt can be essentially complete in some SBDO. I think that statement came from the fact that *most* SBDO move quickly through the Northwest while still largely in alternate plumage, even though we do see some later on that have almost completed this molt; but we actually see very few of them in advanced stages of molt. On the other hand, we see lots of LBDO in all stages of body molt, because they're with us for a considerably longer period than the adult SBDO are (presumably because they are also molting their wings in this region).
I hope that's of some help. I'm still as puzzled as the rest of you about the identity of that July dowitcher, but I'd like to make one further comment about field marks.
I decided to look at the assertion that SBDO has a longer wing projection than LBDO, so I looked at some dowitcher photos easily available to me, in my 1993 shorebird book. Of the 5 photos on pp. 336-337, an SBDO is shown with wingtip not exceeding tail tip (top of p. 336), and an LBDO is shown with wing tip exceeding tail tip (bottom of p. 337), so I don't put much value on this as a field mark.
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