Virginia and All, "why is the Chatfield bird not a Lesser Black-backed?"
This is a valid question and one I meant to address last night. Just posting a Western Gull, a possible first state record with no details is poor, I admit. But I was too busy with work to post anything then, so here goes.
The bird does look very much like a Lesser Black-backed Gull, with 1 major exception, and several lesser exceptions. It's the stuff that makes gulling fun! I first thought it WAS a Lesser Black-backed Gull and said that outloud. "Look, a Lesser Black-backed Gull in breeding plumage". This would be unusual in itself, so I ran back to the car to get my camera to photograph it. As I was taking pictures, I was studying the bird thru my camera lens. I left my scope in Paul Differdings car so that was not an option. I started to notice the bird didn't look quite right for Lesser Black-backed Gull. The mantle was pretty dark, probably a shade darker than the Lesser Black-backed Gulls we see here (graellsii). The bird looked bulky and not slender or long-winged. The eyes were dark. Lesser Black Backed Gull has a pale iris usually after it's second year. In my opinion, the entire look of a bird changes with iris color or eyeline vs. no eyeline etc. The bill was very large with a small, red gony spot. The bill, with a big fat bulbous tip really looked out of place for Lesser Black-backed Gull. Then the bird stood up. It's legs were pink! Lesser Black-backed Gull has yellow legs, at least adults do. We began to really scrutenize the bird at close range. The wing pattern looked good for Western Gull and seemed to eliminate other dark-mantled, pink-legged gulls (Great Black Backed Gull and Slaty Backed Gull). More on wing-pattern later. The orbital ring was bright yellow! This was huge in helping us determine the ID. Orbital ring color is usually only seen in breeding plumage adults at close range. We were lucky enough to have both. The bird showed broad tertials with a broad white tertial crescent and a drooping tertial skirt. This feature helped the already stocky bird, look larger.
Regarding wing pattern... the pattern you see on a flying bird, the 'M' of a juvi Sabine's Gull or 'string of pearls' of a Slaty-backed Gull is made up of each individual feather in conjunction with the next. This can be very important in identifying gulls. Small differences in each feather can change the look of wing pattern. This bird in flight showed a large amount of black in the wing tip and just a small amount of white. Specifically, P10 the outer primary feather of each wing, showed a small white window with a tiny amount of black at the tip. P9 the next primary in, showed most entirely black. This ironically is very similar to Lesser Black-backed Gull (a yellow legged bird) but did eliminated Great Black-backed Gull which has white windows on both P9 and P10. The outter primaries did not show the 'string of pearls' of a Slaty-backed Gull, created from sub-terminal white spots then black then terminal white spots on the outter primaries. This was also huge as Slaty-backed Gull must be considered when looking at a large, dark mantled, pink-legged, adult breeding plumaged gull.
Hybrids must be considered, especially when looking at common west coast gulls. All that observed this bird while I was there made an attempt to look for signs of hybridization. That said, I would love for Steve Mlodinow and others very familiar with left coast gulls to see this guy. As a matter of fact, I suggest everyone go out and study this bird with field guide in hand. This is what makes us better birders!
Thank You Joey, for helping me out with this bird via phone! Glenn Walbek Castle Rock, CO http://www.pbase.com/gwalbek/western_gull -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
