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In the Scope: Mergansers: Identification, ageing, and sexing

TONY LEUKERING Ah, April in Colorado: The beginning of the manic birding season and a period of transition for most of the state’s birders from paying attention to water birds, including lots of ducks, to a fairly tight focus on land birds. April is also a time of transition for many birds, what with prealternate molts to look attractive to the opposite sex and immatures of various bird species molting into adult or, at least, more-adult-like plumages. While many of us might note those White-crowned Sparrows molting from the brown-and-tan immature head plumage to the white- and-black adult head plumage, how many of us have noted the many first-year male mergansers that still look mostly like females in spring?

Mergansers also seem to create identification headaches for many birders. Thus, in the couple of years that I have been pondering writing this essay, the focus has broadened greatly from just first-spring male mergansers to the entire assemblage of post-downy plumages presented by the three Colorado representatives of Lophodytes and Mergus.

While Hooded Merganser (genus Lophodytes) is distinctive enough from Colorado’s two large mergansers (genus Mergus), female-plumaged birds create identification challenges for many birders. Even more importantly, the two large mergansers in female-like plumages engender much confusion. Although the main thrust of this essay is to provide details on ageing and sexing mergansers, that very task provides more certain identification to species by expanding the number of identification features available in birders’ ID toolboxes.

After an introductory treatment about molt and molt timing – yes, it is critical to understanding the various plumages, I describe each species’ progression from first basic plumage (=juvenile plumage) through definitive basic plumage1. Most points are illustrated via the figures and their captions, including the photos presented on the back cover of this issue. Molt timing in mergansers Quite unlike most dabbling ducks and somewhat different from that of many other diving ducks, the plumage transition of first-year mergansers can be protracted, with males still wearing mostly female-like plumage into summer (when a year old). This protraction of plumage transition was the initial point

1 Molt and plumage terminology and definitions follow Howell (2010) and Pyle (1997, 2008). For additional detail about molts and plumage, please refer to Howell (2010) or Pyle (2008)— both of which I have cribbed from extensively—or to the “In The Scope” column that presented a molt-and-plumage primer in a previous issue of this journal (Leukering 2010). I also follow Pyle (2005, 2013) in considering the “bright” plumages of male waterfowl to be basic plumages.

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Pyle (2008) notes that juvenile mergansers can initiate molt out of first basic plumage (=juvenile plumage) as early as August of their first year, with that molt – the preformative molt (resulting in formative plumage; see Leukering 2010, Pyle 2008) – continuing as late as March of the following year. That source also notes that some first-summer (one-year-old) mergansers conduct a limited first prealternate molt (in Hooded, possibly only in non-breeding first-cycle birds, and in all species, possibly only in males) June through August.

I have seen many individual mergansers, particularly of Red-breasted Merganser, wearing female-like plumage late in spring (that is, after March) that are obviously first-year males (see below). Thus, I suspect that the molt period presented by Pyle (2008) is too brief. In fact, a one-year-old Hooded Merganser that summered at Cape May Point, Cape May Co., NJ, in 2008, and identified by nearly all as a female, eventually started growing in male-like plumage in August (pers. obs.). I do note that Pyle (2008) does suggest this slower transition by noting that the crests of first-cycle male Hoodeds are “increasingly mixed with black and white feathering in Dec-Sep….” Additionally, as part of the research into this topic and in search of suitable illustrative material, I looked at >500 photos of Common Mergansers in the eBird/Macaulay Library photo archive2 (Sullivan 2009) and at Flickr3 and found <8 photos of Common Mergansers that I could determine (via plumage, eye color) were immature males, even when restricting my search to November through May. Conversely, there are numerous photos of immature male Red-breasted Mergansers discoverable with similar searches. I suspect that many or most immature male Common Mergansers make the transition to adult-like plumage quite late, if at all. One of the causes of this relative lack of photographic material of immature male Commons in plumage transition may be due to its relatively earlier spring migration (personal observation, eBird 20124), which could mean that the molt takes place mostly on or near the breeding grounds, where they are less accessible to most photographers.

Adult mergansers conduct two molts per year, a complete prebasic molt August- October and a partial prealternate molt May-July. However, it has been shown with many other duck species that males and females of individual species have differing molt schedules, particularly for prealternate molts and Pyle (2008) does indicate that Hooded Merganser prealternate molts are poorly known and require more study.

2https://ebird.org/media/catalog 3www.flickr.org 4https://tinyurl.com/COME-COplains - scroll down to mergansers

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Eye Color As with many other duck species, eye color is a useful indicator of age in mergansers (with caveats), at least from late summer through fall and varyingly deep into winter. Independent juvenile Hooded Mergansers have brown eyes, while those of Common and Red-breasted mergansers have yellowish to yellow- olive eyes. Additionally, as with some other duck species, eye color varies by sex in adults. In Hoodeds, females have brown to olive eyes5, males have bright yellow eyes (Dugger et al. 2009). Common Mergansers have dark eyes in both sexes (brown in female, dark brown in male; Pearce et al. 2015), while adult Red- breasteds have paler eyes, bright red in males and yellow-orange or reddish- brown to dull red in females (Craik et al. 2015).

While you are looking at the eyes, note the color of the nearby plumage. The plumage around the eyes is among the first adult head plumage grown by first- year males transitioning to adult plumage, and any distinctly dark plumage there identifies the bird as a male. Bill Color The bills of Common and Red-breasted mergansers are quite similar in color with extensive orange, reddish, or salmon on at least the mandible, but creeping up onto the maxilla. Adult males, however, have bills almost entirely bright red. Hooded differs quite strongly in this regard: adult males have black bills and any brown merganser with yellow on the bill is a Hooded (female or immature male). Leg Color The legs of the two large merganser species are bright orange or reddish, while those of Hooded are often dull and/or dark, but can be fairly bright yellow. Alternate Plumage In all three species, adult males attain a variably female-like plumage May-July and molt out of that plumage August-October (Pyle 2008, Dugger et al. 2009, Craik et al. 2015, Pearce et al. 2015). Though their crests are reduced in alternate plumage, they retain their adult wing and tail plumage, which can allow ageing and sexing. Adult males in the two large species also develop a juvenile-like white loral stripe in alternate plumage.

SPECIES ACCOUNTS The back-cover photos depict first-year males of all three species of Colorado- occurring mergansers (Figs. 1-3), presented in taxonomic order (as per AOS 2018). All individuals are in plumage that is readily confused with that of females of their respective species. I do not present illustration of adult males, either in basic (bright) or alternate (dull) plumages.

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Hooded Merganser (Figures 4-7)

Figure 4. This Hooded Merganser is wearing the typical juvenile (=first basic) plumage of the species. This plumage presents an appearance that causes many birders fits. Perhaps most critical of the angst-causing features is the lack of the typical crested head shape of Hooded Merganser. However, the long, narrow bill should get us to the mergansers and, once there, the yellow on that bill identifies the bird as a Hooded. Hennepin County, MN; 6 September 2017. Photograph by Brad Argue.

Figure 5. Unlike the bird in Fig. 4, this bird has more of the crested head-shape that we expect out of Hooded Merganser. The presence and coloration of the brown crest contrasting with the gray of the rest of the head, the thin white stripes on the tertials, the dark eye, and the late June date all point toward the bird being an adult female. Tompkins County, NY; 29 June 2017. Photograph by Jay McGowan.

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Figure 6. This bird’s bright yellow eye might be one’s first clue that this Hooded Merganser is not a female. Throw in the streak of white behind the eye, the black plumage around the eye, black back, and black bill and its identification as a one-year-old male is certain. Note that the formative tertials with distinct white stripe is also typical of a first- year male; formative tertials of first-year females have no or indistinct pale stripes. Sacramento County, CA; 1 June 2015. Photograph by R M Yoshihara.

Figure 7. This bird provides a peek into another confounding process in ageing and

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I N T H E S COPE sexing birds. Unlike humans, in which female is the “default” sex (females are homozygous, that is, they have two identical chromosomes – XX, unlike the male heterozygous state – XY), the default sex of birds, when it comes to plumage, is male. That is, female hormones typically suppress the expression of male-like plumages in some birds, including ducks. As estrogen concentrations decline with a female’s age, the suppression of male-like features is reduced, resulting in male-like appearances in older females (Pyle 2008, page 72, and references therein). This Hooded Merganser is probably one such bird, i.e. an older female. While this bird’s plumage might be similar to that shown by some immature male Hoodeds, the November date is too early in the plumage cycle for a first-year male to have molted enough to sport this appearance. A one-year-old Hooded Merganser of this appearance in June or September might be determinable as a one-year-old male, but this bird’s relatively dark eye should rule out that possibility at that time of year, as should other plumage details and the extensively yellow bill. Toronto, Ontario; 23 November 2014. Photograph by Ricky Wong.

Common Mergansers (Figures 8 – 10)

Figure 8. While the sharp meeting of the reddish nape and paler gray neck helps identify this as a Common Merganser, the extensively white foreneck might be considered anomalous. However, this plumage is typical of a first-winter bird and closely resembles one in juvenile plumage. Note the yellowish eye, the distinct white subloral stripe above the brown gape stripe, and near lack of the species’ typical bushy crest. While it is probable that the preformative molt has begun, it is not safe to sex this bird on this date. Cape May County, NJ; 1 December 2013. Photograph by Sam Galick.

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Figure 9. Avoid getting stuck in the adorableness of the photo and note that this adult female Common Merganser lacks the white subloral stripe of first-year plumage (see Fig. 8) and sports a bushy crest and fairly dark eyes. Potomac River, Frederick County, MD; 23 March 2013. Photograph by Dave Czaplak.

Figure 10. Note the scattered white and clump of black feathers in this Common Merganser’s right wing. Since females do not exhibit such plumage, and because it is March, this must be a first-spring male. Alameda County, CA; 19 March 2018. Photograph by David Yeamans.

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Figure 11. This Red-breasted Merganser is in formative plumage, as discerned by yellowish eye and the white subloral stripe (running from bill to under eye). Unfortunately, I could not find a suitable photo of a juvenile Red-breasted, so just imagine that this bird has less crest and is less worn-looking and you will have a picture of a juvenile in your mind’s eye. Pinellas County, FL; 22 December 2013. Photograph by Tony Leukering.

Figure 12. This Red-breasted Merganser can be aged as an older bird by the lack of a white subloral stripe. Given the date, the yellowish eye, and the lack of any obvious male plumage, determination as an adult female is straightforward. Port Clinton, Ottawa County, OH; 14 February 2018. Photograph by Mike and Mary Caldwell.

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Figure 13. This first-spring male Red-breasted Merganser has only a few very dark feathers around the eye; they would not be noticeable at much more than point-blank range. However, the bird’s red eye and, particularly, the incoming black-and-white plumage on the breast and among the scapulars provides proof of age and sex, along with the date, of course. This photo also nicely illustrates the point that there are often many clues as to age and sex of mergansers (and many other bird species), not just the one or two noted in field guides. Learning the appearance of common birds in great detail allows more-accurate ageing and sexing… and more certainty in determining whether the ogled bird is a common species or not. Barnegat Light S. P., Ocean County, NJ; 1 March 2015. Photograph by Sam Galick. ACKNOWLEDGEMENTS I greatly appreciate a thorough review of a previous draft of this manuscript by Peter Pyle. Peter also pegged the bird depicted in Figure 7 as an old female. Any remaining errors are mine.

LITERATURE CITED American Ornithological Society [AOS]. 2018. Checklist of North and Middle American birds. http://checklist.aou.org/taxa/ (Accessed 16 March 2018.) Craik, S., J. Pearce, and R. D. Titman. 2015. Red-breasted Merganser (Mergus serrator), v. 2.0. In The Birds of North American (P. G. Rodewald, ed.). Cornell Lab of Ornithology, Ithaca, NY. Dugger, B. D., K. M. Dugger, and L. H. Fredrickson. 2009. Hooded Merganser (Lophodytes cucullatus), v. 2.0. In The Birds of North American (P. G. Rodewald, ed.). Cornell Lab of Ornithology, Ithaca, NY.

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I N T H E S COPE eBird. 2012. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. Available: http://www.ebird.org. https://tinyurl.com/COME-COplains Howell, S.N.G. 2010. Molt in North American Birds. Houghton Mifflin, New York. Leukering, T. 2010. In the scope: Molt and Plumage. Colorado Birds 44:135-142. https://cobirds.org/CFO/ColoradoBirds/InTheScope/24.pdf (Accessed 11 March 2018.) Pearce, J., M. L. Mallory, and K. Metz. 2015. Common Merganser (Mergus merganser), v. 2.0. In The Birds of North American (P. G. Rodewald, ed.). Cornell Lab of Ornithology, Ithaca, NY. Pyle, P. 2005. Molts and plumages of ducks (Anatinae). Waterbirds 28:208-219. http://www.birdpop.org/docs/pubs/Pyle_2005_Molts_and_Plumages_of_Duck s.pdf (Accessed 11 March 2018.) Pyle, P. 2008. Identification Guide to North American Birds, part II. Slate Creek Press, Bolinas, CA. Pyle, P. 2013. Molt homologies in ducks and other birds: A response to Hawkins (2011) and further thoughts on molt terminology in ducks. Waterbirds 36:77-81. http://www.bioone.org/doi/full/10.1675/063.036.0111 (Accessed 11 March 2018.) Sullivan, B.L., C.L. Wood, M.J. Iliff, R.E. Bonney, D. Fink, and S. Kelling. 2009. eBird: a citizen-based bird observation network in the biological sciences. Biological Conservation 142: 2282-2292.

Tony Leukering, 1 Pindo Palm St. W, Largo, FL 33770 ([email protected])

Figure 1 (Back Cover). The right bird appears to be an adult female Hooded Merganser by the dark plumage without mixed feathers, although caution is necessary as some first- spring males may lack male-like feathers on this date. The left bird, however, is not. While the bit of extra white in the face provides a reasonable clue, this bird’s splotches of black on the chest are proof that the bird is a first-spring male. The March date of the photo is then proof of the bird’s age as something less than a year old. San Diego, San Diego Co., CA; 13 March 2018. Photograph by Chad King.

Figure 2 (Back Cover). This merganser can be identified as a Common by the browner aspect to the head plumage, the distinct and well-defined white chin, and the sharp transition from brownish-red head plumage to white neck. However, ageing and sexing this individual is a bit trickier. The pale eye color identifies it as a first-year bird, while that bit of dark plumage intruding into the white chin patch is all that we need to determine that it is a male. Obviously, at any distance, the bit of adult-like head plumage would not be visible, suggesting that caution is warranted in determining the sex of any Common Merganser in fall and winter that is not wearing adult male plumage, especially those not seen very well. Socorro County, NM; 18 January 2017. Photograph by Jerry Oldenettel.

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Figure 3 (Back Cover). While looking female-like, this Red-breasted Merganser is a first-winter male, a determination that can be made by the bright red eye and the dark patch of plumage around that red eye. Adult male Red-breasteds would have been wearing obvious adult male plumage for many months by this photo’s date. In addition to the red eye, this bird can also be safely differentiated from Common Merganser by the more-orange aspect to the head plumage (see Fig. 2) and the ill-defined border between reddish head plumage and the paler neck. Cape Ann, Essex County, MA; 2 February 2014. Photograph by George L. Armistead.

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Figure 1

Figure 2

Figure 3 In the Scope: Mergansers: Identification, ageing, and sexing...... 92