Second Slaty-backed Gull at Aurora Reservoir?

[quet...@comcast.net]

I joined other frustrated seekers of the adult Slaty-backed Gull on Saturday afternoon, 3 Jan 2014. The Slaty-back eluded us, but we did see part of the gull flock sitting on the ice shelf by the main parking lot/buildings, perhaps 1000 birds, including some interesting gulls:

Glaucous -  1 first-cycle
Thayer's - 2 adults, 2 first-cycle

Lesser Black-backed - 4 adults, 1 first-cycle

California - 1 first-cycle

Hybrid LBBxHerring - 1 adult

Herring - approx. 50

Ring-billed - approx. 900

 

There was also a mystery gull that stumped all of us, but now I think it is a candidate for first-cycle Slaty-backed. I am not at all confident about the identity of this bird, but the closest match I could come up with in Howell and Dunn's Gulls of the Americas is indeed Slaty-backed Gull (see p. 214, figures 30.8 and 30.9). Digiscoped images and some discussion of the bird are posted online at http://www.pbase.com/quetzal/mysterygullah. I will be seeking advice on this bird from others, but better photos are needed. So, if you are at Aurora looking for the adult Slaty-back this weekend, and you have a decent camera, you might want to photograph this bird as well. It may be a second Slaty-backed Gull.

 

Nick Komar

Fort Collins CO

[quet...@comcast.net]

I have uploaded additional photos of the candidate 1st-cycle Slaty-backed Gull from Saturday, taken by David Dowell, at the link below. These include flight shots showing a wings with Thayer's like pattern on the primaries, which is consistent for Slaty-backed Gull. See Howell and Dunn p. 215, photo 30.24 and 30.26. Also Sibley Guide, p. 222.

From post on 1/5/2014:

 

[snip]...There was also a mystery gull that stumped all of us, but now I think it is a candidate for first-cycle Slaty-backed. I am not at all confident about the identity of this bird, but the closest match I could come up with in Howell and Dunn's Gulls of the Americas is indeed Slaty-backed Gull (see p. 214, figures 30.8 and 30.9). Digiscoped images and some discussion of the bird are posted online at http://www.pbase.com/quetzal/mysterygullah. I will be seeking advice on this bird from others, but better photos are needed. ...[snip]