Date: Mon, 3 Jun 2002 10:11:16 -0400 Reply-To: Maryland Birds & Birding Sender: Maryland Birds & Birding Comments: RFC822 error: MESSAGE-ID field duplicated. Last occurrence was retained. From: Harvey Mudd Subject: Re: Pacific Loon In-Reply-To: <3CF96C05.B449205A@comcast.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Bob, While Jim Stasz, Marion and I were admiring the Clopper Lake Pacific Loon last week we carefully noted the width, length and shape of the white flank patches. I have to admit that my mind was fantasizing about the possibility of seeing Maryland's first Arctic Loon. However, upon returning to the car a few minutes later, a recheck of the articles by Andrew Birch and Cin-Ty Lee in Birding 29, 106-115, 1997 and Birding World 8, 458-466, 1995 - both devoted to field identification of Arctic and Pacific Loons, and how to distinguish them, and each with many photos - confirmed that the flank patches we had just seen on the loon in question were entirely compatible with Pacific, and not with Arctic. As summarized (p.111) in the Birding article, "Pacific Loons can show obvious white above the waterline if they are swimming "high" or partly rolling over as if to preen, but they never show the shape and extent of white that Arctics display (Dunn and Rose: Birding 24, 106-107, 1992). The key is to note whether the white on the flanks extends up to the sides of the rump, indicatiing an Arctic Loon". That is, on the Arctic the posterior white patches "flare" to a greater extent above the waterline, rather than forming a straight boundary between the dark sides and the undersides. These features are seen in many of the photos in these articles. Plate 3 in the Birding World article shows an adult summer Pacific Loon with rather broad white flank patches, but they extend only about 60% of the distance from the mid-base of the neck towards the rear, and do not "flare" at the back. With respect to the chin-strap (which we did not see well), the Birding article (p.112) says "On adults in basic plumage, a well-defined dusky chin-strap is diagnostic of Pacific Loon (Figure 10). Some Arctic Loons may show a slight dusky chin-strap (or an impression of one), but it is never an obvious, well-defined feature as it normally is in Pacific Loons. The absence of a chin-strap, however, does not necessarily denote an Arctic Loon, because a small percentage of Pacific Loons, particularly juveniles, can have very faint, inconspicuous chin-straps (Schulenberg: Birding 21, 157-158, 1989)". Harvey Mudd At 08:51 PM 6/1/02 -0400, you wrote: >I got good looks at both the Common and Pacific first-summer >loons this morning between about 10:30 and noon. They were at >least a quarter-mile apart, so I couldn't get a good size >comparison. The Pacific was near the dam the whole time. >(Thanks to John and Carrie Staples for the scope views.) > >I have a couple of related questions that hopefully somebody with >more experience can help with: > >During a portion of the time I was viewing the Pacific Loon, it >showed large white patches on the flanks toward the rear, >reminiscent of the (alternate) adult Arctic Loons I saw in >Alaska. The white patches were comparable the those seen in >the first-summer Arctic picture in Sibley, maybe a little smaller. >Clearly much larger than shown in any Pacific plumage picture I have >found. I have not previously seen either Pacific or Arctic >Loons in first-summer plumage, so I wonder how you rule out >an Arctic Loon? Does the "chin-strap" (seen clearly in some >of Mary Ann Todd's pix) make the difference? It isn't shown >in any Arctic pictures I have found. > >A more general question: The rest of the time I watched, the >white patch wasn't so obvious, presumably because the bird was >riding lower in the water. That's what I want to ask about. >What makes the same bird ride higher or lower in the water? >The amount of food in the belly? It can't be how wet it is, >because the Pac Loon was diving the whole time I was there, but >it waterline definitely changed. > >Thanx for any insight anybody can provide. > > Bob Hartman > Colesville, MD > >======================================================================= >To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com >with the following message in line 1: signoff mdosprey >======================================================================= ____________________________________ S. Harvey Mudd NIMH/DIRP/LMB Building 36, Room 1B-08 36 CONVENT DR MSC 4034 BETHESDA MD 20892-4034 tel: 301-496-0681; fax 301-402-0245 email: shm@codon.nih.gov ======================================================================= To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com with the following message in line 1: signoff mdosprey ======================================================================= =========================================================================