Tuesday, 11 March 2014

Gadwall x Mallard

Gadwall x Mallard hybrid (with Bufflehead), South Platte River, Denver County (Colorado, USA), 21st January 2013 - copyright Cathy Sheeter
(photo ID: 1870)


This is a hybrid that seems to turn up fairly frequently in North America (maybe less often in Europe for some reason?) - often enough to have once been considered to be a species in its own right, known as Brewer's Duck.  Note that intersex Mallards can superficially resemble this (and other) hybrids.  Check the bill - an intersex Mallard with plumage resembling this will usually have a orange and black bill showing a pattern like on female Mallards.

On this bird Cathy describes the head as "incredibly irridescent" - and so it seems in her great photos.


Gadwall x Mallard hybrid (same bird as in photo ID 1870 above), South Platte River, Denver County (Colorado, USA), 21st January 2013 - copyright Cathy Sheeter
(photo IDs: 1871-1872)


This one was probably the same bird:



Gadwall x Mallard hybrid, South Platte River, Denver County (Colorado, USA), 1st April 2013 - copyright Cathy Sheeter
(photo IDs: 1863-1865)


Cathy describes this one as a returning bird at the exact same location - I assume the same one as the bird shown above...

Gadwall x Mallard hybrid (with Gadwall), South Platte River, Denver County (Colorado, USA), 25th December 2013 - copyright Cathy Sheeter
(photo ID: 1843)


Although quite different from the more Malard-like bird above the next pale-cheeked and more Gadwall-like bird is fairly typical for Gadwall x Mallard hybrids.
 

Gadwall x Mallard hybrid, Platte River, Denver County (Colorado, USA), 29th December 2012 - copyright Cathy Sheeter
(photo IDs: 1884-1885)


Another superbly photographed bird below - again a more Mallard-like individual.  This one accpompanied a female Gadwall.





Gadwall x Mallard hybrid, Lakewood (Colorado, USA), 20th April 2011 - copyright Cathy Sheeter
(photo IDs: 1900-1904)


The next more distant bird was among a flock of Gadwall.  Cathy tells us that though not visible in the photos, it did show a very small round tan spot behind the bill, but it had less tan/copper colour on the head than any others Cathy has seen.



Gadwall x Mallard hybrid (with Gadwall), Adams County (Colorado, USA), 29th March 2013 - copyright Cathy Sheeter
(photo IDs: 1866-1868)


The flight shots below show a wing pattern that is intermediate between the two species.  The grey spots near the bill tip are not always present.





Gadwall x Mallard hybrid, St Vrain State Park, Weld County (Colorado, USA), 10th April 2011 - copyright Steve Mlodinow
(photo IDs: 1427-1431)


Not all examples of this hybrid show the pale cheeks like this one.  The next one is such a bird.  The chestnut crown is typical for this hybrid but this bird shows more orange on the bill than usual.



Gadwall x Mallard hybrid, South Platte River, Adams County (Colorado, USA), 29th December 2012 - copyright Steve Mlodinow
(photo IDs: 1233-1235)


Another dark-headed bird follows, although a buffy cheek is more common on this hybrid.  This one also seems to lack the chestnut crown usually seen.  But as Steve points out, beyond the white in the speculum, you can see Gadwall influence in the headshape and in the speckling on the chest.




Gadwall x Mallard hybrid, South Platte River, Adams County (Colorado, USA), 24th November 2013 - copyright Steve Mlodinow
(photo IDs: 1129-1132)


Steve notes that the next bird is much more Mallard like than members of this cross he's seen before.  The bill pattern is fairly good, and the body, with somewhat long tertials is fine, but the chest is darker brown and the head nearly uniform green.  Since there was a "typical" Mallard x Gadwall hybrid at the same site a year earlier, he wonders if this is an F2 backcross with a Mallard.



Gadwall x Mallard hybrid, St Vrain State Park, Weld County (Colorado, USA), 3rd March 2012 - copyright Steve Mlodinow
(photo IDs: 1304-1306)


The identity of the next bird was less straightforward as Steve writes:
"This bird's ID is not as apparent as others of this cross that I have come across.  That which is Gadwall is readily apparent.  However, for the other parent, the green stripe on side of head with buffy-bronze pate suggests that there might be a wigeon in the mix.  On the other hand, the entirely gray body excepting brownish washed chest is quite suggestive of Mallard parentage.  The Mallard x Gadwall that I photographed about this time last year in Colorado [photo IDs 1427-1431 above] actually has a head pattern similar to this bird, with the pale pate being less obvious due to the angle at which the photos were taken.  The pink and black bill pattern is similar to the typical yellow and black bill pattern of Mallard x Gadwall, but unlike the gray and black patterns shown by wigeon x Mallards.  The flight shots shows a back, rump, and tail very reminiscent of Mallard."




Gadwall x Mallard hybrid, South Platte River, Adams County (Colorado, USA), 26th February 2012 - copyright Steve Mlodinow
(photo IDs: 1319-1323)



Gadwall x Mallard hybrid, Prewitt Reservoir, Washington County (Colorado, USA), 26th April 2012 - copyright Steve Mlodinow
(photo IDs: 1280-1281)


For the next bird Steve writes:
"The head/chest gives the Mallard, while the bulky gray body, bulbous head and long tertials bespeak Gadwall.  Mallard x American (or Eurasian) Wigeon can look somewhat like this."

Gadwall x Mallard hybrid, Loloff Reservoir (Colorado, USA), 10th April 2015 - copyright Steve Mlodinow
(photo IDs: 2231-2232)


presumed Gadwall x Mallard hybrid, Sombrero Marsh, Boulder County (Colorado, USA), 4th November 2012- copyright Christian Nunes
(photo ID: 2349)


The next two female birds have a plumage that reminds me of certain domestic Mallards (e.g. Silver Appleyard).  It certainly looks like no Gadwall I've ever seen, so I can well understand why they should be identified as a Gadwall x Mallard hybrid, with the Mallard parent being one of the domestic types that look quite similar.  But Joern has another idea - could a pure female Gadwall show such a plumage due to mutation?  I guess a similar mutation to the one that leads to a domestic Mallard showing this sort of plumage pattern could occur in other similar species.  Many birds at this site have been released for shooting and mutations are more likely to occur among captive populations (presumably due to restricted gene flow and inbreeding?) so Joern's idea sounds feasible to me. 


possible Gadwall x Mallard hybrid or mutant Gadwall? (with Gadwall), Leathes Ham, Lowestoft (Suffolk, UK), 11th March 2011 - copyright Andrew Easton
(photo IDs: 2063-2064)


Andy points out that the next photos appear to show a different bird to the ones above (taken 6 weeks earlier) as the spotting doesn't appear as heavy, the dark markings on the tail are less extensive and the head striping is much stronger.  He also notes that the head and bill shape seem more Mallard-like.  On the other hand the wing pattern which Andy has managed to capture doesn't give any clear steers to point to Mallard influence.  This is a conundrum that requires more knowledge to solve - let us know if you have come across this variant occurring in pure Gadwall elsewhere.  Also more examples of female Gadwall x Mallard hybrids will help us piece things together.


possible Gadwall x Mallard hybrid or mutant Gadwall? (with Gadwall), Leathes Ham, Lowestoft (Suffolk, UK), 22nd April 2011 - copyright Andrew Easton
(photo IDs: 2061-2062)


The next drake is a bit easier, and Steve notes that the solidly dark-headed phenotype is relatively unusual, leading him to suspect that this is the same bird he's been seeing since the winter of 2012-13.


Gadwall x Mallard hybrid, South Platte River, north of Denver (Colorado, USA), 8th January 2017 - copyright Steve Mlodinow
(photo IDs: 2905-2906)



Joern Lehmhus has written about Gadwall x Mallard hybrids in the German magazine Aves.  The text is in German but non-German speakers may still be interested as it's accompanied by several photos of Gadwall x Mallard hybrids.  You can access the PDF of Aves 2 (2011) - the article starts on page 21 with section 5 on this hybrid beginning at page 24.  The photos labelled Abb. 12 to Abb.16 are Gadwall x Mallard hybrids and Abb. 17 is a composite with an illustration of Gadwall x Mallard hybrid wing in the centre.

Joern has also put together this lovely plate showing the variation in head pattern of this hybrid.  It consists of drawings of different birds documented online from North America and Europe.

Gadwall x Mallard hybrids, Europe and North America - copyright Joern Lehmhus
(illus. ID: 3028)


A few times I have come across drake Gadwall showing a white neck collar recalling that of a Mallard.  Sometimes it has been suggested that these birds might be hybrids involving Mallard, perhaps backcrossed, but I do not believe this is the case.  In each case there has been nothing else in the birds' appearance to suggest that any other species is involved other than Gadwall, so it seems much the most likely explanation that this odd feature is just a variation within genetically pure Gadwall.  I include photos of three such birds below as I gusess people may arrive at this page when looking for information about birds like this.


Gadwall showing white collar, Felbrigg Lake (Norfolk, UK), 14th February 2017 - copyright Dave Appleton
(photo IDs: 3036-3037)


Gadwall showing white collar, Sparham Pools (Norfolk, UK), 7th May 2007 - copyright Dave Appleton
(photo ID: 3035)



Gadwall showing white collar, Thurlby Pit (Lincolnshire, UK), 24th January 2017 - copyright Dean Nicholson
(photo IDs: 3033-3034)



Gadwall Anas strepera
Mallard Anas platyrhynchos

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