From south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Tue Sep 23 00:07:39 2003 Received: from www.plaidworks.com (localhost [127.0.0.1]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h8N75LIB012243 for <[[email protected]]>; Tue, 23 Sep 2003 00:05:22 -0700 (PDT) Received: from sccrmhc11.comcast.net (sccrmhc11.comcast.net [204.127.202.55]) by plaidworks.com (8.12.9/8.12.9) with ESMTP id h8N72EZP012149 for <[[email protected]]>; Tue, 23 Sep 2003 00:02:16 -0700 (PDT) Received: from computer.comcast.net (12-234-255-153.client.attbi.com[12.234.255.153]) by comcast.net (sccrmhc11) with SMTP id <2003092307020901100mjg7fe>; Tue, 23 Sep 2003 07:02:10 +0000 Message-Id: <[[email protected]]> X-Sender: [[email protected]] (Unverified) X-Mailer: QUALCOMM Windows Eudora Version 5.2.1 Date: Mon, 22 Sep 2003 23:59:23 -0700 To: [[email protected]], [[email protected]], [[email protected]] From: Alvaro Jaramillo <[[email protected]]> Subject: Re: [SBB] Golden Plover In-Reply-To: <[[email protected]]> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Cc: X-BeenThere: [[email protected]] X-Mailman-Version: 2.1.2+ Precedence: list List-Id: South Bay Birding List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Errors-To: south-bay-birds-bounces+south-bay-birds-archive=[[email protected]] Birders I am trying to keep an open mind on the problem of this Alviso plover. I have looked at some of my photos and tried to work through my logic and I must admit that I still think it is a Pacific Golden Plover. The general question of identifying American and Pacific golden-plovers is one that I got into quite a bit during the preparation of the field guide to the birds of Chile as Chile is a place where Pacific has been reported from but with little evidence. Thus I went through a lot of specimens, measuring wings, and looking at plumage to try and figure if any specimens from Chile were Pacifics - they were not, all were Americans. In any case, it gave me a good appreciation of how variable those wing lengths are and what the general plumage differences look like. I also get a good number of both species each year either in Chile, Alaska, Argentina, and Hawaii. I don't think that identifying these two species is trivial, but I do think that you can parse out some of the variability when you know the age of the bird, state of moult and so forth and you can almost always arrive at a satisfactory identification. I do appreciate that I have not seen the Alviso plover in life, but at the same time an objective study of the photos provided by Tom Grey is a unique and different perspective on it. Also I should note that I am truly interested in figuring out what the identification of this bird is, so that it goes down in the proper 'box' in our understanding of plover migration in the county. Thanks to Bob Reiling and Mike Rogers for bringing up some good points on this bird, and let me try and address these in one way or another. At 01:07 PM 9/22/2003 -0400, [[email protected]] wrote: >All, > >Having the opportunity to look at photographs of the American Golden-Plover >is an interesting exercise but one should use extreme care in determining >things such as color, especially when those photographs were taken under poor >lighting conditions [early morning]. I can't testify for sure as to >digital images >but in the past different types of film yielded fairly different colors [fast >films being too blue and slower films being too red]. In any case no one has >attested to the accuracy of the color seen on the bird in question [I don't >think that we can assume that the color seen in the photos is in fact the >actual color of the bird]. Let's face it, the American Golden-Plover and the >Pacific Golden-Plover are both Golden-Plovers. The Golden-Plover seen >Saturday had >a fairly golden and striped crown and a fairly golden lower back, upper tail >coverts and tertials, the remaining wings were much less golden and therefore >tended to favor the American Golden-Plover identification. Agree, photos can be misleading in terms of colour. Digital images are worst with anything close to white, and often 'bleach' out any pale colours in sun. Warm morning light will make a bird look more golden, but then in the last sentence Bob mentions that the American Golden Plover is fairly golden on the upperparts. Not sure what "the remaining wings" means though. So the bird is golden above, it is not a situation where in life the upperpart pale markings are buff or greyish and the photo makes them look golden. It is golden in life, and perhaps the photo makes them look more golden than they really are. This would be my interpretation of this point. The relevance of how golden this bird is depends on age (we now have it confirmed as an adult) and if those golden feathers are basic (non-breeding) or alternate (breeding) feathers - See Mike's point below. >My feeling is that photographs are useful in backing up visual >identifications when taken during the visual examination and may make for >an interesting >identification exercise but that they have limitations that are not always >obvious. In any case apparent coloring of the bird in question [a highly >subjective >feature] would not take precedence over the long primary extension [fairly >obvious to me in Tom's photos] and the even spacing of the primaries [both >highly objective features]. The bird in question is surely a post >breeding [not >non-breeding] adult American Golden-Plover. Bird identification is a mix of objective and subjective, and this is what makes it one of the most fun bits in birding for me. Trying to bring the subjective into the objective side of the equation is the challenge. Part of this has to do with understanding variation and the statistical distribution of variation, which bits vary a lot and which vary little. Bob is saying that the structural features vary less than the plumage features on these plovers. I don't tend to agree. To make sense of the variation you need to look at each plumage type independently. Golden speckling on the backs of breeding adults of both species is the norm, juvenile American vary quite a bit in how golden they are, and winter Americans show very little golden colour on the upperparts. The wing lengths vary more than you would think, based on my experiences measuring birds in the museum, and there is a region that in the field can look intermediate between the two species. Also most birders that have learnt this feature base probably base it largely on juvenile birds they see in the field, and many photos available of juveniles (easy to approach and more easily findable than adults during migration). Adult and juvenile Pluvialis plovers have different wing structures, juveniles actually have shorter wings than adults, but more importantly their tertials are quite a bit shorter. This gives the average juvenile a moderately different primary and wing projection in the field as compared to an adult. Primary Projection = the projection of the primary feathers past the longest tertial. Wing projection = the projection of the primaries past the tail tip. The other very important aspect to consider is the tertials, if one of the long tertials is missing the primaries will look to be very long - even on a bird that does not have long primaries! The Alviso bird is missing the long tertials at least on one side, and this creates an illusion of a longer wing than what is really there. Mike's message, chopped here and there. >Having read Al Jaramillo's post, the identification of this bird >should be discussed further. Al thought that perhaps the long-winged >appearance of this bird might be "partially an illusion". It is not. >The bird is long-winged, with the wing tip extending well past the >tail tip by a distance that is fairly typical for AMERICAN >GOLDEN-PLOVER in my experience. Mike mentioned this, but I will mention it again. The left side of this bird is missing its longest tertials, making the primaries appear longer than they are (primary extension). The tertials show up on a sitting bird as the group of feathers immediately behind the back scapulars which rest on the folded primaries. On adult Pacific Goldens the tertials reach almost to the level of the tail. I have put two pictures up that show this, both of Pacifics that I took in Hawaii. http://chucao.home.comcast.net/pgpl1.jpg http://chucao.home.comcast.net/pgpl2.jpg The right side of the Alviso bird appears to have the longer tertials not missing, and the primary extension there does not look ridiculously long. I have uploaded one of Tom's photos (thanks Tom) showing this side, with the primary extension (primaries past tertials) highlighted. http://chucao.home.comcast.net/pgpltom1.jpg I realize that the photo is foreshortened due to the angle of the bird, but still this is not such a huge primary extension. Do check out that the left side of the bird has way more primaries showing due to the missing tertial, this is visible on this shot. So if you look at the left side of this bird, the apparent length of the primaries could fool you. Now the wing extension (primaries past tail) are as long as they look, there is no illusion here. Les Chibana made some comparisons which Tom posted: http://www.geocities.com/tgrey41/GoldenPlover2mod.jpg I agree that the wing extension is long for a Pacific Golden Plover, look at my first photo http://chucao.home.comcast.net/pgpl1.jpg for what an average Pacific looks like. But then look at my second photo to see a Pacific that shows a wing extension that is pretty much like the Alviso bird http://chucao.home.comcast.net/pgpl2.jpg I do think that the Alviso bird shows a wing extension on the long end for Pacific but still within what is reasonable. The primary spacing would be interesting to get into in more detail, but I must admit that I would need more reference material to assess how much primary spacing varies on these birds. Most of the primary spacing information I have seen has been based on juveniles, and it is likely that they have a slightly different wing shape than adults, as is so common in non-passerines. The fact that Bill Bousman mentions that the longest and second longest primaries were the same length suggests a slightly more rounded wing, rather than a real pointed wing - I associate this more with Pacific than American, but take that with a grain of salt. The primaries of the Alviso bird look too brownish to be new primaries so I don't think the outer one is growing in. However, this brownish appearance may be an artifact of the photo and the primaries are blackish, new and fresh. If they are, then this bird is definitely a Pacific Golden Plover, as they moult their wings at this latitude and moult earlier. American Golden Plovers wait until they are in southern South America to moult, and they do this much later on in the winter, finishing up in January or February based on what I recall from two southern summers on the coast of Argentina. Another thing to think about is that the fact that this bird is hanging around this long is a bit suspicious, although anything is possible in the bird world. If it keeps on lingering the behaviour points more and more to Pacific which can winter at this latitude. American Golden Plover adults don't fiddle around too much, once they have fattened up nicely in the far north they just haul butt to the southern hemisphere. > The bird is definitely not in its >first fall, as evidenced by the presence of several black spots on the >underparts that do not show well in Tom's photos. Al noted that "the >extensive amount of golden on the upperparts pretty well eliminates >American Golden Plover which is much more grey-brown above as a >non-breeding (basic plumage) adult". This may be true for a basic >individual, but this species molts late (as Al also noted) and >typically retains much alternate plumage during migration. In fact it >seems to me that the bird is still mostly in alternate plumage. Many >adult females (especially one-year old birds) may not acquire much >more black than this individual, suggesting that the underparts may >not have changed all that much as a result of molt. I checked and re-checked the upperparts of the Alviso bird. Tom also sent me the originals so that I could check them out in even closer scrutiny (I need to get a life!). I don't think that most of these feathers are retained breeding feathers, they look like non-breeding (basic) feathers to me. A shorebird, particularly one that breeds in the high Arctic where there is 24 hour daylight or nearly so bleaches, fades and wears in no time. The key features to look at are the pale markings on the upperpart feathers, if these were retained breeding feathers almost all of the pale notches would be gone by now. They would really look bad. This bird has most of the upperparts looking pretty fresh and crisp, some of the lower scapulars and tertials are downright shiny and new. I would argue that these cannot be retained alternate feathers, but new basic feathers. This extends to most of the mantle and the scapulars. Rather than a bird that is moulting late, I think that this is a bird that has moulted in most of the body feathering and is moulting relatively early. The other bit to look at is the actual pattern of the scapulars and upperpart feathers. I have posted a photo of a breeding male American Golden Plover I took in Nome, Alaska. http://chucao.home.comcast.net/agpl1.jpg which shows the general upperpart pattern pretty well. Now females are duller, they retain more basic (winter) feathers in the upperparts, and the breeding feathers they get are a bit less well marked, but the general pattern is the same. Breeding feathers on these plovers show a pale tip (white or golden - more likely white on American, and golden on Pacific) which is split by a black stripe along the vane (midline). At their base there is one set of big pale notches along the edge of the feather; these are not easily seen on most feathers as they are high up and covered by the next row of scapulars. The basic (winter) feather pattern of a Pacific Golden is to show more of a buff or golden edge on the tip, and smaller notching farther up on the feather. Sometimes the edging is really prominent and the notching less so. Overall breeding upperparts look spotted, and winter upperparts look more striped. The Alviso shows a pretty typical pattern for an adult winter Pacific Golden Plover (see the links noted above). Winter American Golden Plovers are a lot duller than this, with pale edging and notching looking more whitish, grey, or buffy-grey than anything. I have yet to see a winter American Golden Plover a lot of golden on the upperparts, certainly never as much as the Alviso bird. A couple of other perhaps more subjective marks have to be added. Adult American Golden Plover appear to have gleaming white or whitish supercilia at all times. The supercilia are the brightest and whitest part of any adult winter American Golden Plover, contrasting with the rest of the face. The whitish supercilia create a diademed look that is quite unlike that of Pacific. Pacific Golden Plovers have whitish to buff to pale golden supercilia which do not contrast much with the rest of the face. This feature also fits Pacific for the Alviso bird. The dark spot on the auriculars is larger and more contrasting on Pacific Golden Plover, as compared to American. Again this feature lines up the Alviso bird with Pacific in my opinion. I apologize that I have no good photos of winter American Golden Plovers to show, next time I am down there I will have my digital camera and I can digiscope a bunch. I do have some poor slides but I don't know if it is worth scanning them. I apologize that my viewpoints may not be what people want to hear. Hey no one hates being the bad guy more than I do, let me tell you. But golden plovers have been a recent interest of mine and I find the subject fun (It is times like this that I realize that I am a bit eccentric). At least I hope that my thoughts are valuable to those that go out there and see this bird and want to come to their own conclusions. Have an open mind! I am often wrong (just ask my parents and my wife, good friends, teachers etc.), yet I still feel that there are enough things that point against American Golden Plover on this bird to make me think it is not one. I apologize if my comment "is this the bird being called an American Golden Plover?" in my initial posting sounded harsh and critical. I have not followed all of this all that closely, and I knew that there was a bird being reported as an American and another as a Pacific so I was confused as to which one of the birds this one was. All for now, Al Alvaro Jaramillo Biologist San Francisco Bay Bird Observatory P.O. Box 247 Alviso, CA 95002 (408)-946-6548 http://www.sfbbo.org/ [[email protected]] ***** NOTE NEW E-MAIL ADDRESS**** _______________________________________________ Do not post admin requests to the list. They will be ignored. south-bay-birds mailing list ([[email protected]]) Help/Unsubscribe/Update your Subscription: http://www.plaidworks.com/mailman/options/south-bay-birds/south-bay-birds-archive%40plaidworks.com This email sent to [[email protected]]