Sunday, 2 November 2014

Yellow-rumped Warbler intergrades

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Holyoke, Phillips County (Colorado, USA), 5th May 2013 - copyright Steve Mlodinow
(photo ID: 1171)


The taxonomic treatment of the eastern and western forms of Yellow-rumped Warbler (known as 'Myrtle Warbler' and 'Audubon's Warbler' respectively) has varied but currently it seems that most authorities treat them as a single species.

Steve says that in Washington state he found about 1 in 200 Yellow-rumped Warblers were intergrades but when he moved to Colorado he found nearer 10% were intergrades.  More recenlty he's suggested it may be as much as 25% in spring (when they are easier to pick out than in fall).

In the first bird Steve notes the pale yellow centre of the throat.  He says it seems to be a common pattern in these hybrids: some yellow at the centre, or nearly all of the throat, with white fringing. 



Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler') (same bird as in photo ID 1171 above), Holyoke, Phillips County (Colorado, USA), 5th May 2013 - copyright Steve Mlodinow
(photo IDs: 1168-1170)


The next one also shows the yellow throat encircled with white.  Cathy also notes the intermediate chest markings.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Veterans Park, Brighton (Colorado, USA), 18th April 2013 - copyright Cathy Sheeter
(photo ID: 1860)


The next bird is a bit more subtle.  Steve draws attention to the total lack of supercilium (an Audubon's feature) yet a fairly Myrtle Warbler like throat (except that yellow on the edge, perhaps).

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Tamarack Ranch SWA, Logan County (Colorado, USA), 29th December 2013 - copyright Steve Mlodinow
(photo ID: 1117)


Spring males are such smart birds!


Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Kodak SWA, Weld County (Colorado, USA), 20th April 2013 - copyright Steve Mlodinow
(photo IDs: 1180-1181)


Like the last one, the next bird has white corners at the back of the throat - normally lacking on Audubon's Warbler.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Longmont, Boulder County (Colorado, USA), April 2012 - copyright Steve Mlodinow
(photo ID: 1291)


Though photographed at the same place on the same day, the next bird is a different individual.  It shares the same throat pattern and on this view you can the narrow white supercilium which Steve points out is inconsistent with pure Audubon's Warbler.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Longmont, Boulder County (Washington, USA), April 2012 - copyright Steve Mlodinow
(photo ID: 1292)


Steve writes about the next bird:
"Note the hint of throat patch curling behind auricular patch (throat patch should be rounded in pure Audubon's) and mild to moderately prominent supercilium (should be absent in Audubon's) . This combination sets off auriculars from rest of head, unlike what is seen in Audubon's.  Also, throat rather yellow (as in Audubon's), but distinctly white chin and hint of some what around edges or throat patch."


Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Longmont, Boulder County (Colorado, USA), 20th October 2011 - copyright Steve Mlodinow
(photo IDs: 1380-1382)


The next bird isn't so obvious.  Steve writes:
"This bird has a very weak supercilium plus a somewhat buffy throat that is minimally flared at edges, thus suggesting Audubon's influence.  Note that the auriculars do not stand out as a distinct patch."

presumed Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Yuma (Colorado, USA), 3rd October 2011 - copyright Steve Mlodinow
(photo IDs: 1389-1390)


Steve says the next one is more clearly a hybrid (though I'm sure many a less careful observer would overlook it).  He goes on:
"Note the mixture of white and yellowish in the throat patch, which is slightly curled upwards at the edges; also note the very weak supercilium.  An Audubon's Warbler should lack any curl of throat patch extending behind the auriculars and should not have bright white in the throat.  A Myrtle Warbler should lack so much admixture of yellow in the throat and should have a more distinct supercilium."

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Haxtun, Phillips County (Colorado, USA), 16th October 2011 - copyright Steve Mlodinow
(photo IDs: 1387-1388)


The next bird shows white corners to the throat and an intermediate supercilium.


Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Longmont, Boulder County (Colorado, USA), 28th April 2011 - copyright Steve Mlodinow
(photo IDs: 1420-1421)


On the next bird, photographed on the same day and in the same place, the intermediate throat pattern is more obvious.



Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Longmont, Boulder County (Colorado, USA), 28th April 2011 - copyright Steve Mlodinow
(photo IDs: 1422-1424)


Steve tells us that some Audubon's Warblers can have dirty white throats during their first winter, but not as bright white as in this next bird.  However the shape of the throat patch is more Audubon's-like and the hint of supercilium is not normal for pure examples of either taxa.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Sylvana, Snohomish County (Washington, USA), December 2010 - copyright Steve Mlodinow
(photo ID: 1452)


Another smart spring male, and Steve notes the white corners extending back from throat and part way around the auriculars (ear-coverts) and the wing-covert edging in between the two taxa.


Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Everett (Washington, USA), April 2009 - copyright Steve Mlodinow
(photo IDs: 1472-1473)


Steve points out that the strongly bicolored throat and hint of supercilium suggests that the next bird is an intergrade.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Dallesport, Klickitat County (Washington, USA), January 2011 - copyright Steve Mlodinow
(photo ID: 1474)


Next is another with intermediate wing covert edging and a yellow centre to the throat with a clear white border surrounding.

 

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Sentinel Bluffs, Grant County (Washington, USA), May 2010 - copyright Steve Mlodinow
(photo IDs: 1475-1476)


Steve says the next bird's throat was moderately white, but the patch was rounded more like that of an Audubon's, and the supercilium was intermediate (not very well shown in this photo).

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Weld County (Colorado, USA), 3rd May 2014 - copyright Steve Mlodinow
(photo ID: 1574)


Steve says the yellow on the throat was more apparent in the field than in the next photo and the white supecilium was also more prominent in life.

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Wray, Yuma County (Colorado, USA), 5th April 2014 - copyright Steve Mlodinow
(photo ID: 1573)


Another subtle bird comes next.  Steve notes "the white throat, starting to curve behind the auriculars and naught but a trace of a supercilium".

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Lake Pena Blanca, Santa Rita County (Arizona, USA), 20th January 2015 - copyright Steve Mlodinow
(photo ID: 1784)


They keep on coming, but who can complain - such lovely birds!


Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Crow Valley, Weld County (Colorado, USA), 21st September 2015 - copyright Steve Mlodinow
(photo IDs: 2287-2288)






Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Greenlee Preserve, Boulder County (Colorado, USA), 2nd May 2010 - copyright Christian Nunes
(photo IDs: 2340-2344)


Christian describes the next one as, "A typical-looking combo, predominantly Myrtle Warbler (dark mask, white supercilium, white throat wraps below auriculars), but with a yellow throat."

Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Confluence Ponds, Boulder County (Colorado, USA), 21st April 2011 - copyright Christian Nunes
(photo ID: 2346)



Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Golden Ponds, Longmont, Boulder County (Colorado, USA), 17th April 2016 - copyright Steve Mlodinow
(photo IDs: 2799-2800)


Steve finds these intergrades common in Colorado strarting from when Myrtle Warblers arrive in late September through to when Yellow-rumped Warblers become uncommon to rare, sometimes November.  On this occasion 10% of over 100 Yellow-rumped Warblers were obvious intergrades, and Steve speculates that had the others been examined in the hand the number of intergrades identified might have been double that.  Heres' one of the 10%...



Yellow-rumped Warbler intergrade ('Myrtle Warbler' x 'Audubon's Warbler'), Berthoud STP, Weld County (Colorado, USA), 27th September 2016 - copyright Steve Mlodinow
(photo IDs: 2872-2874)



Yellow-rumped Warbler Setophaga coronata (formerly Dendroica coronata)
'Myrtle Warbler' Setophaga coronata coronata and Setophaga coronata hooveri
'Audubon's Warbler' Setophaga coronata auduboni, Setophaga coronata nigrifrons and Setophaga coronata goldmani

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