The west coast of North America probably hast more instances of large gull hybridisation than anywhere else. Many are clearly hybrids whilst some are much more subtle and it comes down to micro features and is probably as a result of back crosses thus making the third, or more, generations look more like one of the original parent species than another. Hybrids were commonly seen amongst the larger gull flocks of Salinas River Mouth, Goat Rock Beach near Jenner, Moss Landing, Roberts Lake Parka and other gull areas.
The selection here is just the tip of the iceberg so if you want to see more west coast hybrids click here.
California - November 2009
Hybrid Gulls
Heermann's Gull
Boneparte's Gulls
Mew Gull
Ring-billed Gull
California Gull
Thayer's Gull
Hybrids
Albino Gull sp.
Glaucous-winged Gull
Yellow-footed Gull
Western Gull
American Herring Gull
This bird is clearly not an obvious hybrid but an Albino and about as albino as you can get. The bare parts are faded and washed out, the bill is lacking colour though perhaps the faintest hint of 'red' around the gonys perhaps suggesting the bird is adult and the legs and feet are pink.
Attributing it to species is very difficult as there are a number of features that are consitent and inconsistent was many of the normally plumages large west coast species it is is left unasigned.
This first-winter gull appears to be one of the easier of the hybrids to assign parentage. The head shape, large deep black bill and generally dusky head and body plumage are characteristic of Western Gull whilst the paler wing coverts, tertials and broad pale fringes to the primaries indicate Glaucous-winged Gull influence thus the bird is attributed as a Western x Glaucous-winged Gull hybrid.
As in the previous image this bird can be attributed as a first winter Western x Glaucous-winged Gull based on the same features.
Initially this looks like a normal adult Glaucous-winged Gull however it has a few features not consistent with this. The dark mark on the bill along with the and subdued bill tone indicates that this a near adult whilst the primaries are probably to dark for a pure Glaucous-winged Gull. In addition the eye is pale.
This could be a Glaucous-winged x American Herring Gull which was present at Moss Landing though an atypically pale eyed, extreme dark winged Glaucous-winged Gull could be possible.
Same bird as above. Note the relatively narrow white trailing edge to the primaries and secondaries when compared with pure Glaucous-winged Gull. P10 has a large mirror and there is a white tip to the outer web only and lack of mirror on P9. Presumed Glaucous-winged x American Herring Gull hybrid.
Presumed Western x Glaucous-winged Gull hybrid based on the the dark eye, square head shape, bill shape and the dark, not black, wing tips. This bird was a Bodega Bay Harbour.
Adult presumed Western x Glaucous-winged Gull at Salinas River Mouth. The upper-parts appear to pale for the occidentalis form of Western Gull. There is a single white mirror on P10 however the black of the outer primaries is not as as extensive as found on pure Western Gull whilst the black band on the tip of P5 is very narrow.
Presumed near adult Western x Glaucous-winged Gull at Borega Bay. Note the heavy hooded affect indicating a Glaucous-winged Gull influence whilst the darker upper-parts blackish primaries and bill shape indicate Western Gull. It is possible that this is a occidentalis form Western Gull however the heavy head streaking is at the extreme for a pure Western Gull.