COBirders,
If you look at gulls, and what birder doesn't, but you don't know where to 
start when viewing thousands of birds coming to roost, consider starting with 
mantle color on adult birds.  Steve Howell and Jon Dunn presented a Kodak Gray 
Scale guide to adult gulls as recorded in their Gulls of the Americas.  Here is 
a condensed version from their book for adult gulls seen in the winter in CO 
and also included are a few other CO gulls for comparison.  This should help 
for finding a Mew Gull and maybe for finding a Black-tailed Gull.
Gray Scale light to dark, 0 - 17.
0 - Ivory Gull; please give me a call if you see this one
3-4 - Glaucous Gull; subspecies from Canada and Greenland
3.5-4.5 - Ross's Gull 
4-5 - Glaucous Gull, subspecies from Alaska
4-5 - "Kumlien's" Iceland Gull
4-5 - Ring-billed Gull
4-5 - "American" Herring Gull
4.5-5.5 - Little Gull
5-6 - Bonaparte's Gull
5-6 - California Gull from the northern interior of N.A.
5-6 - Thayer's Gull
5-6 - Glaucous-winged Gull
6-7.5 - California Gull from the southern interior of N.A.
6-7.5 - Mew Gull
6.5-7.5 - Black-legged Kittiwake from the North Atlantic
7-8 - Black-legged Kittiwake from the N. Pacific
8-9 - Franklin's Gull
8-9.5 - Black-tailed Gull
9-11 - graellsii Lesser Black-backed Gull 
9.5-11.5 - Slaty-backed Gull
13-15 - Great Black-backed Gull
14-15.5 - Kelp Gull from South America
Bill Maynard
Colorado Springs
 
 
 
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-- 
Colorado Field Ornithologists: http://www.cfo-link.org/
Colorado County Birding:  http://www.coloradocountybirding.com/

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