Friday, February 14, 2014

Evidence of Prealternate Molt in Long-tailed Ducks wintering on the Great Lakes - 08 Feb 2014

Note: Modified 2/18/2014 thanks to input from Tony Leukering and references from Pyle, 2008.

This winter's cold snap has offered a rare opportunity for Great Lakes birders. With ice covering almost 85% of the Great Lakes wintering waterfowl have been forced to concentrate in the remaining open waters available to them.  This was evident with a spectacular concentration of Long-tailed Ducks on the St. Clair River just south of the Blue Water Bridge in Port Huron, MI on 08 Feb 2014.

Earlier in the week reports of thousands of Long-tailed Ducks were reported at Marysville and at Port Huron. During most winters these ducks can be found as far south as Lake St. Clair, but typically are mostly concentrated on Lake Huron here on the east side of the State. Lake Michigan on the west side of the State hosts impressive numbers of these birds, as well. Today, though, I arrived at the Blue Water Bridge expecting to see thousands of birds at the mouth of Lake Huron, but found only a handful of flying birds.  When I turned my gaze downstream a half-mile, I found clouds of moving waterfowl.





I pulled the Nikon V1 out and decided to capture a quick video of the birds with the hopes of counting them afterward.  Reviewing the video frame-by-frame I estimated 40-50,000 Long-tailed Ducks moving in just this ~1 mile stretch of river.


With so many ducks so close to shore I decided to spend some time photographing and digiscoping birds of various plumage-aspects so that I could further explore the difficult task of aging/sexing Long-tailed Ducks on their wintering grounds here in the Great Lakes.  I made an initial attempt last January and posted my notes w/ my guesses. As I reviewed my images (almost 2000) I came to the conclusion that there is evidence that some of these birds are actively in a prealternate molt prior to returning to their breeding grounds farther north.  This makes aging/sexing even more difficult since there are now transitional appearances to these ducks.

Pyle (2008) summarizes the plumage change in Long-tailed Duck. Plumage worn by adult LTDU through the winter is the basic plumage, and that worn in the summer is alternate. In ducks and geese it is the basic plumage that is typically more colorful and what most of us would consider 'breeding' plumage. Birds less than 1 year of age wear a formative plumage during winter, which is a mix of juvenal and formative feathers. Tony Luekering was kind enough to send me a synopsis of plumage change in LTDUs:

July -- egg hatches; chick leaves nest (fledges); and via first prebasic molt, replaces downy plumage with first "hard" feathers -- juvenal plumage [=first basic plumage]

Nov-Mar -- youngster replaces much of first basic plumage during preformative molt (see below for specifics of plumage replaced) into formative plumage

Jun-Aug -- youngster conducts, at most, a limited prealternate molt ("a few feathers, occasionally 1-4 tert[ial]s and/or a few proximal [near the body] s[econdary] cov[ert]s, and sometimes 1-4 c[entral] rect[rice]s.")

Aug-Dec -- youngster replaces all plumage during its second prebasic molt (because LTDU achieves definitive basic plumage -- that is, adult plumage -- in its second cycle, "second prebasic molt" is equivalent to "definitive prebasic molt" in the species), achieving its first "adult" plumage when about 18 months old.


So, as before, I'll start with the easiest birds first.  Adult males. White head, clay-colored face, black cheek patch, white scapulars and brown-black feathers, and a long tail streamer (r1 retrix) make these handsome birds easy to identify. The  pink band on the bill help distinguish the males from the females that have blue-gray bills.











Non-breeding males are easy to differentiate from females by their white scapulars and pink bills, but aging is not straightforward.  Let's start w/ the image at left. The forefront bird appears to be a male w/ pink bill and chocolate brown crown, and uniform brown scapulars. If we assume a juvenile / 1st winter bird (~7 mo), then is the bird behind it a 2nd winter (~19 mo) male? Note the white head and long white scapulars and bright pink bill.
The remaining ducks are presumed 1st winter females based on dusky brown heads, blue-gray bills, and pale gray scapulars.

Here's another possible 2nd winter male in front of a presumed 1st winter female. After taking this image both birds dived, giving me opportunity to capture their retrix (tail) feathers. The next image is a composite of two images so as to compare male/female retrices.

According to Pyle, the r1 (central tail feather) on the male bird in front is good for a 1st winter bird, with 2nd year birds having a longer central tail feather (see below)!  So this raises several questions: Is this a 2nd winter male? or rather a 1st winter male in formative plumage that typically involve molting of only head and back feathers (Howell, 2010)? Pyle mentions that some HY/SY males will molt their central r1-r3 feathers that could make them appear like the female in the rear of the image. Given the lack of pink on the bill we  might assume this one to be a juvenile / 1st winter bird.

As this duck has disappeared below the surface we can see that r1 is longer than the adjacent retrices, suggesting a 2nd winter bird (note also the presence of white outer retrices), but could also be a 1st winter bird in formative plumage that has molted r1.

This possible 2nd winter male shows white on the crown and worn scapulars. Pink bill is dull and brown feathering suggests possible 1st winter bird? I'm inclined to call it a 1st winter male.

This apparent male in adult non-breeding plumage lacks a distinct tail streamer, but the long, white scapulars, bright pink bill, and yellowish eye suggests a 2nd/3rd winter bird in definitive (adult) basic plumage.
Note the long tail streamer on this male. 2nd Winter bird in pre alternate molt? Lack of white scapulars may suggest that the brown feathers may be new ones? Wow...

This is a presumed non-breeding adult male (3rd winter?) by the extent of clay mottling on face. The long tail streamer is slightly evident.

Here's a suspected adult male in prealternate plumage. Possibly a 3rd winter male? Note the long streamer and clay mottling to face. With the pink bill becoming dull this bird can be mistaken for a female. Pyle (2008) states that the definitive pre alternate (DPA) molt can commence on non-breeding grounds and complete on breeding grounds.  Luekering mentioned that his extensive experience w/ LTDUs in spring at Whitefish Point and and spring on the Atlantic coast in New York and New Jersey has confirmed this.




The females are equally challenging. Lets start with a presumed adult female basic as evidenced by white head, dark bill, and brown/rufous scapulars. Note the length of the longest scapulars with rufous edging replacing the gray/white edging of a 1st winter female.

Here's a similar-looking female but with a dark crown and cheeks. Adult female w/ prealternate aspect?

How about this one? Similar to the previous, but pale fringes to scapulars might suggest 1st winter? Eyes have a distinct yellow coloration that suggests adult, as younger birds seem to have darker brown eyes (I couldn't find any references to eye-color, however).

A similar-looking female, but dark eye and buffy face and mottled chest, and pale edgings to scapular might indicate a 1st winter female in formative plumage.

A suspected 1st winter female by dark cap and uniform, worn, gray/brown scapulars. Breast is dusky and not brown like the adults above.

Suspected 1st winter females w/ dark cap and pale/gray scapulars.


Suspected adult female and 1st winter female.

Longest scapulars on this female are fringed brown/rufous and head is pale. 1st winter female?

I wish to thank Janet Hinshaw for directing me to the Birds of North America Online (bna.birds.cornell.edu/) database for extensive descriptions of Long-tailed Ducks, and to Tony Luekering for his most-valuable insights.  After reading his responses, and re-reading Pyle's accounts, along w/ Howell's explanation of molt, I have a better idea of what I'm facing when trying to age these birds.  As confounding these Long-tailed Ducks are, I can't wait to get back up to Port Huron for more pics, and hopefully a better idea where these birds are in their molt cycles.

Some flight shots to add to the mix.  At this point I consider them pretty pictures...:)















References:

Howell, S.N., Molt in North American Birds, Peterson Reference Guides, 2010, Houghton-Mifflin Press.
Pyle, P., Molts and Plumages of Ducks (Anatinae), 2005, Waterbirds 28(2): 208-219.
Pyle, P., Identification Guide to North American Birds, Part II, 2008, 140-143.
Howell, M.D., Grand, J.B, Flint, P.L. Body Molt of Male Long-tailed Ducks in the Near-Shore Waters of the North Slope, Alaska, 2003, Wilson Bulletin, 115(2), 170-175.
Robertson, Gregory J., and Jean-Pierre L. Savard, Long-tailed Duck, Birds of North America Online, Cornell Lab of Ornithology (ban.birds.cornell.edu/bna/species/651/articles/appearance).

3 comments:

Todd Butkowski said...

Jerry,

It was a pleasure to meet you that day in Port Huron. I did go back the next afternoon and the Long-tails were still in there only more downstream toward the Black River. So much fun to photograph! I stopped at various locations on my way home and did capture two adult White-winged Scoters in the open water near the Marysville golf course. Great weekend to be out with a camera!

K Peck said...

Jerry,

My Mom and I stopped along the St. Clair River on February 19th, to enjoy seeing the "glass" appearance of the water, and to our surprise and delight, we found this massive population of ducks that I had never seen before. I noted their markings (and wished I had my camera), so I could do my research at home. And with your blog, you made my day as I now I know what we experienced was the opportunity to see a beautiful display of this mob of Long-tailed ducks. As you mentioned 40-50 thousand....fascinating. Thank you. Beautiful photography!

Matt said...

awesome post, one I'm going to come back to. you could build this into a major article if you wanted.

if Leukering says they're a 2 year duck how is the male aged as a 3 y.o.?

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