Monday, May 30, 2011
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Solution by Tony Leukering
The answer to this week's quiz photo is "delayed plumage maturation." If you are confused, it is because you might not have known that the question was "What is the cause of this apparent intermediate plumage in a male Hooded Merganser?"
As is true for all ABA-area merganser species, Hooded Merganser exhibits delayed plumage maturation: males do not molt into definitive plumage in their first calendar year. As in many species of diving ducks (but very few dabbling ducks), transition in males from juvenal (= first basic) plumage to definitive (adult) plumage is quite variable in speed and timing. Additionally, some changes in hormone levels can cause changes in the appearance of feathers grown during this molt, even in individual tracts of feathers, if hormone levels change during the molt. This can result in more-adult-like feathers to be grown adjacent to less-adult-like feathers produced in the same molt.
How these two variables -- molt timing and hormone levels -- have combined to produce our quiz bird's odd plumage will certainly never be known, but the only other real possibility is a hybrid diving duck; probably one involving Hooded Merganser. Though Hooded Merganser is known or suspected to have hybridized with six other species of ducks (including two species of dabbling ducks; see Pyle, P. 2008. Identification Guide to North American Birds, vol. II, page 151), the most frequent such hybridization known is with Common Goldeneye. Such hybrids are well known and are found with some frequency in Colorado, though that frequency is something less than 1/year. Less well-known, but still of more than extremely rare occurrence, is hybridization with Barrow's Goldeneye and Bufflehead.
The extensive black on the head, neck, and upperparts indicate that our quiz bird is a male, as does the extensive white behind the eye. However, the sides are gray-brown and the tertials are not the long black-and-white feathers that male Hooded Mergansers sport in basic plumage. Though there has been little replacement of underparts feathers, we can see the beginning of the two black vertical stripes on the upper side of the chest of male Hooded Merganser.
If we wish to entertain hybrid options, we need to find some plumage or structure feature that is not present in any male Hooded Merganser. Our bird's bill is thin and longish like that of Hooded Merganser, without any widening and flattening that we might have expected with any Bucephala genes being admixed in the genome. Additionally, our bird's eye is yellow as in Hooded Merganser and the two goldeneye species, but unlike the dark eyes of Bufflehead. The tail is dark gray like that of Hooded Merganser, unlike the paler gray of Bufflehead and the black of the two goldeneye species. Finally, there is no suggestion of iridescence on the head that would be present on all three Bucephala ducks and no white before the eye, as in goldeneyes.
So, with no particularly anomalous features, our quiz bird must be simply an oddly-plumaged Hooded Merganser that was deftly noted and photographed in mid-February 2010 by Mary Keithler at South Platte Park, Jefferson Co., CO.
Incorrect species provided as answers:
Ring-necked Duck x Hooded Merganser - 2
Eared Grebe - 1
Bufflehead x Hooded Merganser - 1
Congratulations to the 23 of 27 getting the quiz correct:
Answer: Hooded Merganser
Answer: Hooded Merganser