A nice flock of White-winged Scoters

Although White-winged Scoter is very common in winter along the east coast of the US and Canada, they are rarely found close enough to shore to see plumage details, or at least rarely in large numbers. In late November 2016, a huge flock of this species built up off Crane Beach, Massachusetts. The 700+ birds were feeding on an unidentified species of mollusk for a period of roughly one week, very close to shore (at least by scoter standards). The Crane Beach flock provided an exceptional opportunity to study a large number of individuals, which I couldn't let pass.  Despite the freezing ocean breeze on a very windy day, I managed to take a good number of pictures that show the variability of some key characters well.

White-winged Scoter, three adult males, three adult females, and a first-winter male (center).

Below I present a small sample of my pictures from that day, with the goal of revisiting and testing some of the standard identification and ageing criteria. All pictures were taken on November 23rd, 2016, in Massachusetts. Note that due to the warm light of the sunrise most birds look very brown-tinged, but they usually look much darker in the overcast light conditions that are typical of NW Europe.

Adult males (including second-years)

Here are some pictures of adult males showing the variability of the bill pattern, the white tick mark at the eye, and the extension of brown on the flanks. As is well known, the characteristic head shape and the bill pattern allow a straightforward separation from both Stejneger's and Velvet Scoters.

White-winged Scoter, adult male. Massachussetts, USA, November 2016.

This male (below) presents a "hint of horn", not very different from that shown by some Stejneger's, and a quite equilateral nostril. The "two-stepped" head profile, lacking the oval, eider-like shape of Stejneger's, is still very obvious.

Some second winter individuals completely lack the white mark behind the eye, whereas in others it's present but is still shorter than in older birds. Head and bill shape, including the markedly two-stepped profile, is usually not fully developed at this age and some still show a relatively flat head profile. Bill tip is uniformly pink, with thicker black margins than in adults.  Lack of the tricolored bill pattern of adults is also typical of a young age. Some of these young adult males seem to lack the brownish feathers on the flanks, and look more uniformly black than adults, including very reduced amount of white on the greater coverts.

White-winged Scoter, second-winter male (center), with two older males on the back. Massachussetts, USA, November 2016.Immature features include greyish iris, pinkish bill lacking orange tones, short white mark behind the eye and blackish (not brown) flanks.

White-winged Scoter, second-winter male. Massachussetts, USA, November 2016. Note still extensive black on GCs, pinkish bill lacking orange tones, and lack of white mark behind the eye.

[Ageing female-type birds]

Ageing of female-plumaged birds is often simple, as many adult females are completely dark. Differences in the head shape, the shape of the wing coverts (which are uniformly fresh and rounded in juveniles, and more squared in adults) and the paler belly in juveniles are also supportive. However, the most important feature for me is probably the pattern of the GCs, and in particular, the presence of white tips. The pattern is usually difficult/impossible to see when the birds are on the water, so it usually requires pictures in flight:

• adult females: completely dark inner GCs, but the white tip sharply increases in size in the outer 4-5 GCs and can occupy almost the entire feather

• first-year males: usually a small spot at the feather tip, of uniform size in all the GCs

• first-year females: very small or completely absent white spot in all GCs

I guess ageing criteria are the same for Velvet, but I never had the chance to look into the subject in detail in Europe (Velvet is regular but scarce in Spain).  I usually find it problematic to understand the pattern and variability of s1, which is sometimes described as the key feature to age these scoters, so won't make further comments on this feature.

White-winged Scoter, adult female. Massachussetts, November 2016. Note square-shaped, large feathers on the flanks typical of adult birds, and extensive white on GCs.

White-winged Scoter, first-winter male. Massachussetts, November 2016. Small, rounded feathers on the underparts are typical of juveniles, and mostly dark GCs except for the white tip.

White-winged Scoters. Massachusetts, USA, November 2016. First-winter male (front) and adult female (back) . compare difference shape of the belly and flank feathers: juvenile feathers are small and rounded, and adult feathers are broader and more squared-shaped. Note also difference in head shape between males and females.

Adult females

Adult females vary from very dark birds (looking like a "dirty" version of adult males) to those having the more classic brown plumage with two pale areas on the face. I think that the first type is actually more common than the latter; the number of these overall black birds within the population appears to be equal to around 70% of the number of adult males in the population.  I wonder if there is an age-related variability in this feature...

White-winged Scoter, adult female. Massachussetts, November 2016. Note typical shape of the adult feathers in the underparts & flanks.

White-winged Scoter, adult female. Massachussetts, November 2016. Like adult males, adult females also show black upperparts contrasting with browner flanks. Some birds display pink tones in the bill, but note fully dark iris typical of females compared to first-winter males.

White-winged Scoter, adult female. Massachussetts, November 2016. Adult birds show brighter legs than first-winter birds; note also amount of white on the GCs and dark underparts with square-shaped flank feathers.

The black-plumaged individuals are sometimes identified as first-year males with an extensive first prebasic moult, but I think that's not the case based on the GCs pattern (see the shots in flight above), the bright color of the feet, the dark irises, and the squared wing coverts on most birds.

The head shape of these birds actually recalls that of adult males, with a squarish head and the hint of a bump at the bill base, leading to a two-stepped head profile, although it is much smoother than in males. The contour looks flat or slightly concave, and although the differences are subtle, I find them separable from Velvet in most cases. Take a look at this compilation to get a sense of the variability in head and bill shape in adult females:

Note that some adult females present some diffuse pink "brush-strokes" at the bill tip.

First-year males

By late November, juvenile males still look very fresh, and the pale velvet at the base of the bill often looks nicely neat. Around 50% of males already show signs of moult around the face, and a few also have a pale greyish iris and pink in the bill. But even birds that still have a completely juvenile appearance can be readily sexed by the elongated bill and very flat head profile, in contrast to females , which show a shorter bill and often a slightly angular (concave) head profile.

Regarding the separation of White-winged from Velvet, in addition to the head shape, the shape of the feathering at the base the bill is quite distinctive given sufficiently close views; it extends further onto the bill than in Velvet and forms a 90-degree angle in the lower corner, always below the position of the nostril. A few more examples of first-year (presumed) males:

White-winged Scoter, first winter male. Massachusetts, USA, November 2016.

White-winged Scoter, first winter male. Massachusetts, USA, November 2016. The elogated head shape is quite obvious in some males.

White-winged Scoter, first winter male. Massachusetts, USA, November 2016. This bird combines a very juvenile plumage (velvety and with small rounded feathers on the breast) with a brush of pink in the bill and a already slightly pale iris.

White-winged Scoters. Massachusetts, USA, November 2016. This picture shows birds of various ages; compare the head shape of the first winter male (front) with two first-winter females to the right and left, and an adult female on the background (the dark bird showing most of its belly).

White-winged Scoter, MassachuSsetts, USA, November 2016. This interesting bird, likely a first-winter male based on head and bill shape, shows a rounded shape of the feathering at the bill base, reminiscent of Velvet and diverging from the classic right angle of White-winged Scoter.

First-year females

Undoubtedly the most problematic group, many first-year females look very similar overall to Velvet Scoter. With short bills, and often concave and rounded head profiles, it may be extremely difficult to pick one out among a flock of Velvets. However, the shape of the feathering at the base of the bill, even if it is not as distinctive as it is in males, is still quite a good character when properly seen. Most birds (>60-70% ?) clearly show a right angle, below the nostril:

In a few birds the angle is not as sharply defined, looking rounder and closer to the nostril, and the pattern is probably consistent with Velvet. But this seems to be the exception and not the norm!

White-winged Scoter, first winter female. Massachusetts, USA, November 2016.

White-winged Scoter, first winter female. Massachusetts, USA, November 2016.

White-winged Scoter, first winter male. Massachusetts, USA, November 2016. There’s some variation in the extension and pattern of the pale patches of the head.

White-winged Scoter, female. Massachusetts, USA, November 2016. Difficult to age with certainty in this picture.

White-winged Scoter, first winter female. Massachusetts, USA, November 2016. A good example of a bird with rounded feathering at the bill base, which in combination with a concave head profile make this bird tough to separate from a Velvet Scoter.