Montana Field Guide

Medium-sized white-headed gull; male slightly larger than female. Definitive plumage, combination of dark gray mantle, yellow green legs, and black and red spots on gonys (enlarged part of lower mandible where left and right halves come together) distinguish this species from all other gulls in its summer range.

In the Bozeman area, normal migration periods are March 25 to May 15 and again during August 1 to November 25, with peaks April 15 and September 25 (Skaar 1969). Adult California Gulls that were marked on the breeding colony at Freezeout Lake were later reobserved on the Pacific coast from Vancouver, Canada to Baja California, Mexico (Rothweiler 1960).

In the Bozeman area, the California Gull prefers larger lakes, but also occurs on ponds and rivers, especially in spring and fall (Skaar 1969). In Montana, colonies are typically located on islands (Rothweiler 1960). Nests are located either among dried vegetation or on bare ground (Rothweiler 1960)

At Freezeout Lake, stomach contents included insects, oligochaetes, crustaceans, amphibians and birds, and plant material believed to be ingested incidentally to consuming animals (Rothweiler 1960).

At Freezeout Lake, in nesting colonies with Ring-billed Gulls, the nesting habitat is segregated with respect to vegetative characteristics, and food niches are separated by different foraging distances (Baird 1976).

At Freezeout Lake nests varied in shape from depressions in the ground to constructed mounds; they were located 2 to 75 feet apart (Rothweiler 1960).