Photographed 30 Jan 2010 at Erie Reservoir in Boulder County, Colorado, this adult "herring gull" shows several features of Vega Gull, Larus vegae, including wingtip pattern (close match to both Vega and western American Herring Gull, L. smithsonianus, according to drawings in Olsen and Larsson), thick white trailing edge of inner wings, thick white tertial crescent, darker shade of gray on mantle. Head streaking mainly on nape and pale eye is consistent with some (not all) Vega Gulls. The pale pink color of feet matching that of the legs is a feature of American Herring Gull, as Vega should have brighter pink feet. The accompanying bird is a 1-cycle Thayer's Gull, L. thayeri (more images of this bird at https://pbase.com/quetzal/thgu1cy ). Click on image to enlarge.