Whenever I happen to see field notes or a boat trip list from eastern or mid-western birders who are on their first visit to the Monterey Peninsula, I often find that they have recorded the presence of "Herring Gulls" at Pt. Pinos or on Monterey Bay, often in some numbers. Most glaringly, one finds this species listed in September or early October. While Herring Gulls are present at these locales in small numbers in winter, they are essentially absent before late October. What these out-of-state observers noted was variation in Western Gulls (both photos), either some pale-backed birds (first photo; an adult) among darker-backed individuals, or very pale-eyed individuals (second photo; a third-winter bird). The Monterey Peninsula attracts very dark-backed wymani Western Gulls from southern California, and very pale-backed nominate occidentalis from Oregon & Washington. Our local nesters are somewhere in between. The first photo is about the palest bird I've ever seen, and it may actually show introgression with Glaucous-winged Gull, but the head is unmarked in February and the wingtips look very blackish, suggesting an extremely pale-backed Western. Eye color is extremely variable in Western Gull (contra some literature). In all cases, notice the short, thick, bulbous-tipped bill so characteristic of Western Gull. The gonydeal angle is particularly pronounced. Out-of-staters often just assume that Herring Gull is as widespread here as it is in the East, and therefore don't pay much attention, but Herring Gull is quite local in Monterey County.
To the right is a flight shot of a real Herring Gull offshore (third-winter plumage with tail band). Note the big but long bill without much gonydeal angle, the "fierce" or "mean" look to the head, and the pale gray back, in addition to the pale eye. Also the head is heavily streaked in winter, while all adult Western Gulls remain white-headed throughout winter (in my opinion, any streaking on the head of an adult Western in winter is either evidence of (a) young age, maybe just barely 4th year, or (b) introgression with Glaucous-winged; this opinion is contra published works on gulls).
Western Gulls are common throughout the year along the shores of Monterey Bay (esp. rocky shores) and down the Big Sur coast, although migrants from northern and southern populations are here primarily in Oct-March. They are very rare inland (only a handful of records at the Salinas wastewater ponds, only 7 miles upstream from the coast). The distribution of Herring Gulls is quite different. They are common at two local roosts (in Moss Landing harbor and at the Little Sur R. mouth) but must less common along the rest of the coastline (regular, but at smaller numbers, at the gull roosts at Salinas and Pajaro R. mouths, scarcer still at Pt. Pinos and Carmel R. mouth). Good numbers vist the Marina dump. But they are most common well offshore -- farther offshore than most Monterey Bay boat trips. Pelagic trips in Monterey Bay from October into May will have a few Herring Gulls, but one must get 30-50 miles offshore before they are the dominant gull, and then they are often the only larger gull present in the 50-100 mile offshore zone.
PHOTOS: The adult light-backed Western Gull was at Roberts Lake, Seaside, Monterey Co., on 22 Jan 1999; the pale-eyed Western Gull was in the Monterey harbor on 25 Feb 1998. The flight shot of 3rd-winter Herring Gull was near the Davidson Seamount, Monterey Co. (60 miles offshore), on 17 Nov 1979. All photos © D. Roberson.
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