Monday, 2 June 2014

Western Grebe x Clark's Grebe

Western Grebe x Clark's Grebe hybrid (with Clark's Grebe behind), Potholes Reservoir, Grant County (Washington, USA), 2nd July 2009 - copyright Steve Mlodinow
(photo ID: 1462)


Steve gets to see a lot of these hybrids.  He writes,
"As a very rough estimate, I'd say 2000 Western/Clark's Grebes breed on Potholes Reservoir, about 80-90% of which are Westerns.  Somewhere between 1-5% of pairs are mixed "pure" birds, and a similar proportion of individuals are apparent hybrids.  Birds with intermediate calls and young have also been heard/seen."
About this one, paired with a Clark's Grebe, he notes the white in the lores, not consistent with Western Grebe, particularly in alternate plumage.  The bill is intermediate in colour, with a bright orange-red spot at base of the lower mandible (typical of Clark's not Western).  Another photo of the pair is below.

Western Grebe x Clark's Grebe hybrid (with Clark's Grebe behind, same birds as in photo ID 1462 above), Potholes Reservoir, Grant County (Washington, USA), 2nd July 2009 - copyright Steve Mlodinow
(photo ID: 1463)


The next one is paried with a Western Grebe.  Steve points to the intermediate bill color and the pale lores.  They're not normal in alternate plumage Western Grebes, and this white, not in basic either.  The sides are whiter than typical for Western Grebe (compare the hybrid with its mate).

Western Grebe x Clark's Grebe hybrid (right, with Western Grebe asleep to the left), Potholes Reservoir, Grant County (Washington, USA), 3rd July 2009 - copyright Steve Mlodinow
(photo ID: 1461)


For the next one Cathy writes:
"This bird shows more resemblance to a Western Grebe in regards to bill color and size, thickness of black down the back of neck (observed in the field) and color of flanks, however the bright white lores and facial white extending to top of eye indicate some likely Clark's parentage.  Quite possible an F2 generation hybrid back to Western."


Western Grebe x Clark's Grebe hybrid (with Western Grebe - hybrid is on left in first photo and at back in second photo), Frederick Rec Center, Frederick (Colorado, USA), 18th October 2013 - copyright Cathy Sheeter
(photo IDs: 1854-1856)


Here is Steve's commentary on the next pair:
"Note that the bird on the left has a face pattern intermediate between Clark's and Western.  And though its bill is bright orange, the red spot at the base of the mandible is not present (usually, but not always, present in breeding Clark's) and that there is some black along bottom edge of mandible, which should be lacking in Clark's.  I thought the bird on the right was a Western, but the small amount of white in the lores, the relatively bright bill, and restricted dark along bottom of mandible make me wonder if this is a hybrid back-crossed with Western."

Western Grebe x Clark's Grebe hybrid(s), Windsor (Colorado, USA), 21st April 2011 - copyright Steve Mlodinow
(photo IDs: 1425-1426)


Then next hybrid is not overly obvious and might be passed off as an aberrant Western Grebe with extra white in the lores.  But Steve notes that the black cap passes mostly over the eye - whilst this can sometimes be seen in winter-plumaged Western Grebes, it is not normal in summer.  The bill color is typical for Western Grebe in summer, however, in the first picture below you can see (if you enlarge it) a bit of reddish-orange at the base of the mandible and along the line connecting the eye to the bill.  Also, the line between eye and bill is usually not visible in breeding birds because that area is all dark, and this bird's sides are at the very pale end for breeding Western Grebe.  So, Steve summarises, the face pattern is intermediate, but shows a character (the red) that should not be present in Western Grebe.  The flank color is intermediate and the bill colour pretty much Western, except for the small amount of orange at base.



Western Grebe x Clark's Grebe hybrid, Windsor (Colorado, USA), 11th June 2011 - copyright Steve Mlodinow
(photo IDs: 1412-1414)


The next bird is more obvious than the last, but is still more like Western than Clark's.  Steve explains:
"For Clark's, note the orange-red at the base of the mandible and bright white loral spot which extends partly over eye.  For Western, note that the white does not pass over eye, so they eye is not surrounded by white.  Also, there is a dark line along bottom of bill, a mark which Clark's should not show.  The bill color as a whole is intermediate.  Finally, the line connecting the eye to the bill is dark, like a Western (usually not obvious as it is surrounded by dark feathering).  In breeding plumage Clark's, this line is red"


Western Grebe x Clark's Grebe hybrid, Windsor (Colorado, USA), 18th June 2011 - copyright Steve Mlodinow
(photo IDs: 1399-1401)


The next bird is more like a Clark's Grebe, but Steve describes why it's a hybrid:
"In a breeding plumage Clark's, the black should pass further above the eye (on thumbnail view, the dark barely seems to clear the top of the eye).  Also, the flanks are typically paler on Clark's than on this bird.  Finally, the line connecting bill to eye should not have a dusky stretch (though perhaps this is within range of Clark's).  The extensive black on the culmen seems beyond the range of Clark's Grebe, but photos show rather typical Clark's with an equal amount of dark on culmen.  This bird is similar enough to Clark's that it could be an aberrant bird, but watching it amongst a couple hundred Western and Clark's Grebes, it's intermediate nature seemed more striking than in the photos."

Western Grebe x Clark's Grebe hybrid, Windsor (Colorado, USA), 18th June 2011 - copyright Steve Mlodinow
(photo IDs: 1397-1398)


Steve's next shots are among his best, in my opinion.  This one is a bird I suspect I would have overlooked as a Clark's Grebe.





Western Grebe x Clark's Grebe hybrid, Windsor (Colorado, USA), 20th April 2013 - copyright Steve Mlodinow
(photo IDs: 1182-1184)


On the next bird, Steve draws attention to the Clark's-like bill, the more Western-like face pattern (though not quite right for Western, especially in breeding plumage) and the Western-like hind neck.



 Western Grebe x Clark's Grebe hybrid, Lower Latham Reservoir, Weld County (Colorado, USA), 28th April 2013 - copyright Steve Mlodinow
(photo IDs: 1174-1176)


The next pair are both hybrids.  The one Steve identified as the male (based on size) has a rather classic Clark's Grebe bill, with a bright orange spot at the base of the mandible but the lores are like those of a Western.  On the female Steve says the lores are intermediate between Clark's and Western and the bill color was more orange-tinged than most Western.



Western Grebe x Clark's Grebe hybrids, Fossil Creek Reservoir, Larimer County (Colorado, USA), 19th June 2013 - copyright Steve Mlodinow
(photo IDs: 1157-1159)


On the next bird Steve notes the intermediate face pattern, the bright orangey base of bill, intermediate sides, as seen in the photo of the bird sleeping, and the narrow hind-neck stripe.


Western Grebe x Clark's Grebe hybrid, Pagosa Springs, Archuleta County (Colorado, USA), 17th April 2014 - copyright Steve Mlodinow
(photo IDs: 1576-1577)


For the next bird Steve notes the sides are like Clark's Grebe, the bill like Western Grebe; the eye is in the white but the cap touches the top of the eye, atypical for Clark's Grebe.  There is some bare red skin connecting eye to bill, as in Clark's Grebe.


Western Grebe x Clark's Grebe hybrid, Windsor Reservoir, Weld County (Colorado, USA), 14th October 2015 - copyright Steve Mlodinow
(photo IDs: 2292-2293)


Western Grebe x Clark's Grebe hybrid, Frederick Rec Area, Weld County (Colorado, USA), 20th October 2012 - copyright Steve Mlodinow
(photo ID: 2304)


On the next bird Steve notes that the white lores are sharply demarcated from eye and cap and the bill is more richly colored bill than that of Western Grebe. In the field the sides appeared a bit paler than they do here.  Although Clark's Grebe breeds at this location none were present at the time of these photos - only Western Grebes.



Western Grebe x Clark's Grebe hybrid, Lake John, Jackson County (Colorado, USA), 25th September 2016 - copyright Steve Mlodinow
(photo IDs: 2869-2871)



Western Grebe Aechmophorus occidentalis
Clark's Grebe Aechmophorus clarkii

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