Thursday, 5 June 2014

Western Gull x Glaucous-winged Gull

Western Gull x Glaucous-winged Gull hybrid, Mukilteo, Snohomish County (Washington, USA), 31st January 2011 - copyright Steve Mlodinow
(photo ID: 1453)


There is an extensive overlap between the ranges of Western Gull and Glaucous-winged Gull and in that overlap zone (between southern British Columbia and southern Oregon) the two species readily hybridise.  Hybrids (known as Olympic Gulls) are not only fertile but in the centre of the zone they have superior fitness over pure birds.  Consequently there is a hybrid swarm of birds showing the full specturm of appearance between the two pure species.

For the bird at the top of this page Steve notes that the wingtips and back are too dark for pure Glaucous-winged Gull and not dark enough for Western Gull.  The bill is stout and the primaries short, which are unlike American Herring Gull x Glaucous-winged Gull hybrids which also typically have a paler mantle.

Steve points out that next bird is much like a first-cycle Western Gull, but the folded primaries are not dark enough and tipped pale.  Its bill is heavy for American Herring Gull x Glaucous-winged Gull hybrid, and the hint of a dark mask is suggestive of Western Gull heritage.

Western Gull x Glaucous-winged Gull hybrid, Everett, Snohomish County (Washington, USA), 25th January 2011 - copyright Steve Mlodinow
(photo ID: 1457)


Steve captured the same bird in flight, where he points out that you can see that the pale on inner webs of the primaries is too extensive for pure Western Gull. The wingtips are much too dark for Glaucous-winged Gull. American Herring Gull x Glaucous-winged Gull hybrid would usually have a more obvious pale panel on the inner primaries.



Western Gull x Glaucous-winged Gull hybrid (same bird as in photo ID 1457 above), Everett, Snohomish County (Washington, USA), 25th January 2011 - copyright Steve Mlodinow
(photo IDs: 1454-1456)


On the next bird Steve notes the dark mask of a Western Gull and the rather dark plumage overall with more Glaucous-winged Gull like primaries (but with primary tips still too dark for that species).


Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo IDs: 1363-1364)


The next couple of birds are adults and Steve notes the intermediate wing pattern, and back colour more like Western Gull.

Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo ID: 1360)



Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo IDs: 1361-1362)


Here's another showing more etensive dark on the primaries and back a bit darker than one would expect on pure Glacuous-winged Gull.


Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo IDs: 1358-1359)


Steve notes that the next one looks as if it might be a American Herring Gull x Glaucous-winged Gull hybrid, but the lack of pale panel on inner primaries suggests that it is Western Gull x Glaucous-winged Gull.  There is too much dark on primaries for pure Glaucous-winged Gull.

Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo ID: 1357)


For the next one Steve again alludes to the grey on the wing-tips being more extensive and a tad darker than on a pure Glaucous-winged Gull.  It has the head and neck markings of a basic plumaged Glaucous-winged Gull but a mantle color that is more Western-like.



Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo IDs: 1354-1356)


The next bird is more like Western Gull, but Steve points to the dark eye and heavy markings on the head and chest. Western Gulls should be white headed/chested, or nearly so. Many/most have pale eyes, though this is highly variable.

Western Gull x Glaucous-winged Gull hybrid, Elwha River Mouth, Clallam County (Washington, USA), 28th October 2011 - copyright Steve Mlodinow
(photo ID: 1353)


Steve says the next basic adult bears some resemblance to a Slaty-backed Gull x Glaucous-winged Gull hybrid.  Most of those would show more streaking (vs. smudging) on head and neck than seen on this bird, but on the other hand, there is more streaking here than is typical for Western Gull x Glaucous-winged Gull.  The black on outermost primaries is more extensive than would be seen on Slaty-backed Gull x Glaucous-winged Gull, the white "tongues" should be more extensive - it should extend to P8 - and P9 would most commonly have a white mirror on Slaty-backed Gull x Glaucous-winged Gull.




Western Gull x Glaucous-winged Gull hybrid, Westport (Washington, USA), 20th November 2010 - copyright Steve Mlodinow
(photo IDs: 2188-2191)


On the next bird Steve thinks the light eye might suggest Herring Gull parentage, but the dark mantle and large bill are more consistent with Western x Glaucous-winged.

Western Gull x Glaucous-winged Gull hybrid, Westport (Washington, USA), 18th December 2008 - copyright Steve Mlodinow
(photo ID: 2202)


The primaries are not dark enough for pure Western Gull on the next bird:

Western Gull x Glaucous-winged Gull hybrid, Westport (Washington, USA), 16th September 2010 - copyright Steve Mlodinow
(photo ID: 2201)


The next bird is extremely close to pure Western Gull but has the diffuse smudging on the head as in Glaucous-winged.  Steve tells us that a recent study on birds breeding on Protection Island (near the border of Jefferson/Clallam Counties in the Straits of Juan de Fuca) showed all birds in the colony (thousands) to be hybrids, genetically anyway.

Western Gull x Glaucous-winged Gull hybrid, Clallam County (Washington, USA), 26th October 2012 - copyright Steve Mlodinow
(photo ID: 2305)



Western Gull x Glaucous-winged Gull hybrid, Mukilteo (Washington, USA), January 2011 - copyright Steve Mlodinow
(photo IDs: 1464-1465)




Western Gull x Glaucous-winged Gull hybrid, Mukilteo (Washington, USA), January 2011 - copyright Steve Mlodinow
(photo IDs: 1466-1468)


Western Gull x Glaucous-winged Gull hybrid, Mukilteo (Washington, USA), 30th December 2010 - copyright Steve Mlodinow
(photo ID: 2192)


The remaining photos are mine, taken on a holiday in British Columbia.  I'm not greatly experienced with North American gulls, especially Pacific ones, so my identifications are tentative.  I did get some help soon after I posted the photos online for the first time, so hopefully the IDs are accurate, but I have used the word "probable" to reflect my lower level of confidence compared to the ones identified by Steve.

probable Western Gull x Glaucous-winged Gull hybrid, Clover Point, Vancouver Island (British Columbia, Canada), 9th September 2006 - copyright Dave Appleton
(photo ID: 0530)



probable Western Gull x Glaucous-winged Gull hybrids, Boundary Bay (British Columbia, Canada), 9th September 2006 - copyright Dave Appleton
(photo IDs: 0531-0532)



probable Western Gull x Glaucous-winged Gull hybrids, Esquimalt Lagoon, Vancouver Island (British Columbia, Canada), 9th September 2006 - copyright Dave Appleton
(photo IDs: 0533-0534)


probable Western Gull x Glaucous-winged Gull hybrid, Rathrevor Park, Vancouver Island (British Columbia, Canada), 11th September 2006 - copyright Dave Appleton
(photo ID: 0535)


probable Western Gull x Glaucous-winged Gull hybrid, Oyster Bay Shoreline Park, Vancouver Island (British Columbia, Canada), 12th September 2006 - copyright Dave Appleton
(photo ID: 0536)



Western Gull Larus occidentalis
Glacous-winged Gull Larus glaucescens

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