California Gull, Larus californicus

The two pictures above show adult birds in breeding plumage; note the red orbital ring and gape. Below, several adult birds in winter plumage.

Above and below, third summer birds, plumage close to adult.

A third winter bird, showing black tail feathers, left, battles with an adult.

Above and below, first summer birds, the one above more worn and faded, the one below retaining more of the brown first-year plumage.

Here's a juvenile California Gull, taken in late August, and soon to molt into first-winter plumage.