Many thanks to all who participated in this difficult, yet instructive exercise. I found these three plovers to be particularly vexing. Identification of molting adult golden-plovers must rank near the top of the spectrum of difficult identification problems in North America. My original reaction was that bird #3 was an American Golden-Plover because of the extremely long primary projection. The difference in primary projection in these birds is caused not so much by a difference in primary length, but more by a difference in tertial length. Americans have much shorter tertials than Pacifics. There is a difference in the position of the tertials with respect to the tail, but I do not think there is a useful difference in the position of the primaries with respect to the tail.
I agree bird #3 is molting tertials, but I could not quite imagine full grown tertials concealing all those primaries. In fact I feel that only the inner tertials have been molted and the remaining feather is the longest (outermost) tertial. Thus I am not convinced that molt is affecting primary projection at all. Colin Bradshaw (pers. comm.) concluded the same. When public comments began coming in, I was swayed by several experienced birders suggesting that these birds were all Pacific Golden-Plovers although I was still distressed about bird #3 and was not happy that all three were necessarily the same species.
Al Jaramillo correctly pointed out that American Golden-Plovers molt later in the season than Pacific Golden-Plovers. "The Macmillan Field Guide to Bird Identification" by Harris et al. stresses "American Golden usually retains much of its summer plumage until it reaches winter quarters." However, recently published photographs of putative American Golden-Plovers in Birding World (12:362 & 12:388, 1999) taken in September and October of this year show birds which have undergone considerable body molt. I contacted several birders with experience in the East and they indicated that adult American Golden-Plovers usually show extensive body molt by late August. There is a significant difference in the timing of primary molt, but I cannot find any published research which deals with the timing of body molt in these two species.
Dennis Paulson (in lit. to Don DesJardin) said:
I looked at all three jpegs, and my immediate response is that plovers 1 and 2 are Pacific, plover 3 American. This is based entirely on shape. I really think 1 and 2 look short-winged and long-legged, while 3 looks long-winged and short-legged (although not as much of its legs can be seen, I concede). There's nothing about the plumages that will tell us anything, I don't think, but to my eyes they really do fall into two classes with regard to shape. In previous years, when shorebirds were more common here and I watched them more, I often saw mixed flocks of the two species, and I felt they could be distinguished especially when you could compare them. But I still think that some individual birds may prove difficult.....
Alf Tore Mjös wrote:
At first glance, my impression was that the two birds on the left were Pacifics, and the bird on the right an American. I forwarded the link to Ingvar Byrkjedal, author of "Tundra Plovers". He agrees, and say:
- left: Pacific, female
- middle: Pacific, male
- right: American.
I see from the discussion that several others have reached a similar conclusion. I can confirm that Ingvar really knows these birds - he has studied them intensively both in North America and in Siberia.
Matt Heindel wrote:
....My view has not changed much. The first two look like Pacifics to me, the third is more like an American. But, and here is my caveat for the day, since I believe adult Americans to be scarce in CA, I would not identify it as such based on that photo.....
Several other experienced observers wrote similar comments. I found this entire experience to be instructive and humbling. I still think the third bird is probably an American, but I agree with Matt and others, that it may not be enough to establish a firm record.
Thanks again to all who participated. I am in your debt.
The original images are below:
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