Thanks to Steve for his thoughtful and informative contribution to the discussion about this gull. For readers who don’t like inconclusive, overly-detailed and lengthy essays about impossible-to-identify immature gulls, hit the delete key now...
Here is a link to photos/discussion of a similar gull from California. Note its all white head. It was thought by some to be a pale first-cycle Slaty-backed Gull, and by others to be (you guessed it...) Herring x Glaucous-winged hybrid, which apparently is a hybrid combination that can look like just about anything. In other words, it is often suggested as an explanation for oddly-plumaged gulls. In particular, first year hybrids of that combination can mimic young Thayer’s and Slaty-backed Gulls (the latter from Alaska/Asia). It should be noted also that this hybrid combo is common on the West Coast, and in recent years, several individuals likely to be this combo have made it to Colorado in winter, presumably from Alaska, where both Glaucous-winged and Herring breed. Sometimes hybrids show characters that are different from either parent. In the Estes gull, four plumage characters don’t seem consistent with either juvenal Herring or juvenal Glaucous-winged. These are the obviously whiter head, the extensive white in the base of the tail (both parent types normally have all dark tails), crisply barred scapulars (back feathers), and greater coverts (the lower wing panel, when sitting) that are heavily marbled with white barring. There are other gulls that breed in Alaska, and more commonly in Siberia, that DO have these characters: --Slaty-backed has whiter head, and frequently shows pale base of tail. --Vega Gull (the East Siberian form of Herring Gull which also breeds in parts of Alaska, considered a unique species in Eurasia) has whiter head, pale base of tail, barred scapulars, and marbled greater coverts (all 4 characters!). Glaucous-winged Gull is also a common breeder along the North Pacific coast of Asia, and its hybrids with Slaty-backed and with Vega frequently are seen in Japan in winter. All of the plumage characters of the Estes gull can be readily attributed to one of the parents in these hybrid combos. The heavily marbled greater coverts and barred scapulars especially recall Vega. Some photos of juvenal Vega in Olsen and Larsson’s Gulls of North America, Europe and Asia show a small, Thayer’s-like bill. I suppose that Glaucous-winged x Herring would include Vega (as a subspecies of Herring). I think Glaucous–winged x Vega better explains the Estes gull than does Glaucous-winged x American Herring. Nick Komar Fort Collins CO From: Steven Mlodinow Sent: Monday, November 12, 2012 10:32 PM To: cobirds@googlegroups.com Subject: [cobirds] Estes Gull Greetings All Applauds to Tony for a superb discussion of this bird. This series of photos backs my argument about photos being hard evidence. They are ... and they are not. In some photos, this bird's bill looks tiny and Thayer's Gull like In others, approaching that of a GW Gull. The photos are almost all over-exposed, leading to an assortment of other assessment issues. To me, the bird is clearly part GW Gull. No Thayer's Gull is going to have the shape of this beastie (egads, I'm starting to pick up Leukeringisms). Using the series at Nick's PBase site, the last photo (6808) shows primaries that are too dark for any "pure" GWGU. This is also evident in 6785, and methinks in 6746. In 6746, the duskier outer primaries with inner window is really good for GW x Herring Gull. Herring Gull would have darker outer primaries, GW Gull more restricted and less evident dark, not forming that contrast with inner primaries. Why the primaries in 6820 and 6789 look fine for GWGU is beyond me. The bill is showing some paler color at the base. My experience is that GW Gulls should still have all black bills at this date, but some first year Herring Gulls are starting to show pale on the base of their bills by now. So, taking the photos in together as a whole, I do believe this is a GW x Herring Gull. Good Birding Steven Mlodinow (Back from Baja) Longmont, CO -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com. To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com. To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
