Author Archives: Guillermo Rodriguez

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Female Common Eider plumages in the western Atlantic

by Guillermo Rodríguez

Eiders have been a recurring topic of Birding Frontiers, and Martin really pushed the boundaries of Eider subspecies identification. However, most of the effort so far has focused on males, and females have gone largely forgotten. It’s time to change that! Along the East Coast of North America, where at least 2 subspecies regularly occur (the local breeder Dresser’s Eider S. m. dresseri and the arctic Northern Eider S. m. borealis), identification of females is relatively easy, and studying them here is useful for understanding the phenotypic variation. Massachusetts hosts tens of thousands of wintering Dresser’s, and in a few spots they are very close to shore, allowing great opportunities for study.

Given that both subspecies have been recorded in Europe, but only/mainly in adult male plumage, it’s interesting to take a look at some females to raise awareness about how distinctive these birds are. As far as I know, the plumage variation of borealis is poorly known due to lack of information from the breeding grounds, so this post contains a lot of speculation!

Dresser’s Eider dresseri

dresseri is the default subspecies in the US and southern Canada, with an extensive intergradation zone with borealis along the Labrador Peninsula. There are several features that differ from both borealis and mollisima, and identification might be possible in most individuals.

Bill lobe: reminiscent of the massive bill of males, female dresseri show very long lobes, almost reaching the eye, which often look thick and always present a blunt and rounded tip. If seen close enough, the pattern of the tip is absolutely diagnostic in almost all birds, and even at long distances they give a characteristic look. There is a huge variability in lobe length and thickness, apparently without correlation to age or geography.

Nostril position: as in mollisima, nearly all individuals show overlap of the nostril with the feathering at the bill base.

Bill color: dark blue, with a reduced and contrasting greenish tip, duller in first-winter birds. On average they have a small nail.

Head shape: typically flat-topped, with the forehead relatively short leading to a profile that is dominated by the straight contour of the large bill. My impression is that the crown is longer and the bill is shorter than in mollisima, leading to a more square-looking head, as opposed to the elongated bill (and consequently profile) typical of mollisima.

Plumage coloration: adult females are typically rusty or orange-tinged, with most first-winter females being browner and darker. Nevertheless, variation is extensive and adults vary from dark brown to creamy pale, whereas first-winter birds sometimes look very reddish and adult-like even in the first prebasic plumage. The cheek is often neat, lacking any dark streaking.

Tertials: richly colored in adults, typically with a rufous fringe and darker feather center, but the pattern is quite variable and sometimes they show vermiculated or almost entirely rufous tertials. Plain brown in juvenile and second-winter plumages.

Sails: some adult females show small black scapular sails, not as large as in adult males but definitely distinctive if present, compared to mollisima.

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Dresser’s Eider, adult female. Massachusetts, February 2017. Picture by Guillermo Rodríguez

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Dresser’s Eider, adult female. Massachusetts, February 2017. Picture by Guillermo Rodríguez

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Dresser’s Eider, female. Massachusetts, February 2017. Picture by Guillermo Rodríguez

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Dresser’s Eider, first winter female. Massachusetts, December 2016. Picture by Guillermo Rodríguez

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Dresser’s Eider, first winter female. Massachusetts, December 2016. Picture by Guillermo Rodríguez

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Dresser’s Eider, first winter female. Massachusetts, December 2016. Picture by Guillermo Rodríguez

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Dresser’s Eider, first winter female. Massachusetts, December 2016. Picture by Guillermo Rodríguez

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Dresser’s Eider, females. Massachusetts, January 2017. Picture by Guillermo Rodríguez. Note extensive color variation even in adult females

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Dresser’s Eider, females. Massachusetts, January 2017. Picture by Guillermo Rodríguez.

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Dresser’s Eider, adult female. Massachusetts, January 2017. Picture by Guillermo Rodríguez.

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Common Eider ssp, adult female. Massachusetts, December 2016. Picture by Guillermo Rodríguez. Interesting bird, very dresseri-like in plumage but showing pointed lobes. Likely an intergrade dresseri/borealis ?

Northern Eider borealis

Nearctic borealis overwinters around Greenland, reaching Newfoundland but quite rare further south (see below). I have experience only with vagrants in Massachusetts, but Bruce Mactavish kindly allowed me to study and show here some of his pictures from Newfoundland. Males from Newfoundland show orange bill but rounded lobe tips, likely suggesting these birds are relatively southern breeders in Greenland, as the high Arctic breeders are expected to show more pointed lobes.

Bill lobe: short and sharply pointed, and thus very different from dresseri, but probably not very distinctive if compared to mollisima.

Bill color: extensive pale greenish tip, sometimes with a more gradual transition towards the dark blue of the lobe. They often present a marked and pointed nail.

Nostril position: often no overlap of the nostril with the bill feathering, but there is definitely some variation and birds showing overlap aren’t rare.

Head shape: the bill height is very short in borealis, sometimes strikingly so, giving rise to a peculiar head shape. The triangular bill meets the rounded head forming a marked angle and leading to a usually concave head profile. In addition, the bill is remarkably short, especially the distance from the bill feathering to the bill tip – this feature is sometimes quite eye-catching.

Plumage coloration: it seems that birds overwintering in Newfoundland present two main “morphs” – rufous and pale grey – with all sort of intermediates. Whether this difference in plumage coloration is due to some geographical variation or just represents the plumage variation within a single population is yet unresolved. The fact that the few available pictures from N Greenland show completely grey females – whereas dresseri is usually reddish – suggests to me a clinal variation, but with the current evidence it’s difficult to say.

Wing bars: as in all other Common Eider subspecies, adult females present white tips on greater coverts and secondaries, forming two parallel white bards in the wing. This feature is in general quite variable, but in borealis the bars seem to be on average thicker and more obvious than in dresseri and mollisima.

Tertials: usually dull brown, or with at most rufous on the fringes.

Sails: pictures from Newfoundland don’t show obvious sails in females, but see below.

Note that most/all individuals shown here are adults: juvenile borealis seem to be quite rare, or at least in much lower proportion in the population than in dresseri, perhaps as a consequence of strong hunting pressure in Greenland & Canada?

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Northern Eider, adults. Newfoundland, March 2010. Picture by Bruce Mactavish.

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Northern Eider, adults. Newfoundland, March 2010. Picture by Bruce Mactavish.

Out of range borealis – some examples from Massachusetts

Borealis is scarce or rare on the East Coast of the US, with most accepted records involving adult males. However, females seem to be more regular, and given the striking differences in lobe pattern and overall coloration, they are much easier to separate from the local form than in Europe, where the similarity with mollisima hinders finding vagrant borealis. But certainly they are out there; several females have been claimed alongside confirmed males in the UK.

Among flocks of dresseri, female borealis look slightly smaller and less bulky. The measurements given in the Reever guide also suggest a smaller size compared to mollisima (but may depend on the population).  Most of the females seen in Massachusetts are of the striking pale grey morph, but it’s likely the proportion is also biased because they are the easiest to pick out from a distance. All five of the birds I’ve seen had neat pale cheeks and a distinctive pale eyebrow.

The bird below is a rufous adult female, quite similar to many of the birds from Newfoundland. Both the lobe length and the bill are fairly short, giving her a distinctive appearance.

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Northern Eider, adult female. Massachusetts, January 2017. Picture by Guillermo Rodríguez.

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Northern Eider, adult female. Massachusetts, January 2017. Picture by Guillermo Rodríguez.

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Northern Eider, adult female. Massachusetts, January 2017. Picture by Guillermo Rodríguez.

This second bird is a more typical pale grey/creamy adult female. Note all the key characters – pointed lobe, extensive pale bill tip, clean cheek, pale eyebrow, dull tertials, and hint of sails.

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Northern Eider, adult female. Massachusetts, February 2017. Picture by Guillermo Rodríguez.

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Northern Eider, adult female. Massachusetts, February 2017. Picture by Guillermo Rodríguez.

Some of the females seen in Massachusetts and neighbouring states are very striking. Too striking, perhaps. For instance, take a look at this amazing bird found by Marshall Illiff and Ryan Schain off Cape Cod, MA, on December 2011. This adult female differs from the typical borealis from Newfoundland and other vagrants seen in Massachusetts – note the heavy head, flat crown, large size, and even the shape and length of the lobe. Is it possible that this bird shows some influence from sedentaria, the subspecies that breeds in the Hudson Bay and spends the winter in polynyas in the frozen sea? Very little is known about this subspecies, not to mention the potential intergradation with borealis at Baffin Island and its surroundings. Do some birds from this region actually take the eastern route and spread out into the western Atlantic? Hopefully we will discover more about this fascinating topic in the future!

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Northern-type Eider, adult female. Massachusetts, December 2011. Picture by Ryan Schain.

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Northern-type Eider, adult female. Massachusetts, December 2011. Picture by Ryan Schain.

I would like to thank Bruce Mactavish and Marshall Illiff for insightful discussion about nearctic eiders.

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A nice flock of White-winged Scoters

by Guillermo Rodríguez

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.

Below I present a small sample of my pictures from that day, with the goal of revisiting and testing some of the identification and ageing criteria (presented in eg Garner et al. (2004), Reeber (2016)).

WARNING! This post contains many pictures!

All photos 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.

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The mollusk they were feeding on – Eastern Slippery Shell?

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White-winged Scoter: a juvenile male (right at the center) with three adult females and three adult males.

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.

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White-winged Scoter, adult male.

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White-winged Scoter, adult male. Note the particular shape of the flank feathers.

This male (below) presents a “hint of horn”, not very different from that shown by some Stejneger’s (see, for comparison, the Stejneger’s seen in December in Alicante, Spain), and a quite equilateral nostril. The “two-stepped” head profile, lacking the oval, eider-like shape of Stejneger’s, is still very obvious.

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White-winged Scoter (left) and the recent Stejneger’s Scoter (right) from Alicante, Spain. The Stejneger’s picture © Jana Marco, one of the finders of this mega!

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.

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White-winged Scoter, second year male, lacking white tick mark.

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White-winged Scoter, second year male, with limited eye tick mark.

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White-winged Scoter, “young” adult male (presumed 2w), showing typical immature features such as greyish iris and pink bill, lacking any yellowish or orangeish tones.

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White-winged Scoter, adult male (left) and a male showing some immature traits (right), eg short eye tick mark, pink bill and not fully developed bill knob.

[Ageing female-type birds]
Ageing of female-plumaged birds is often simple, as many adult females are completely dark and even jet black. 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 meadial 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 or at most a gradual and slight increase, but always occupying <50% of the feather
first-year females: very small or completely absent white spot in all GCs

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White-winged Scoter, adult female: note largely white medial GCs, bright reddish feet, squared wing coverts, very broad primaries.

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White-winged Scoter, adult female.

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White-winged Scoter, first winter male: limited amount of white in the GCs

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White-winged Scoter, first winter male.

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White-winged Scoter, first winter female.

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 I won’t make further comments on this feature.

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 much more common than the latter; the number of these overall black birds within the population appears to be only slightly lower than the number of adult males eg from a sample of 205 birds, 14.6% were adult males and 12.2% were these black presumed females. I wonder if there is an age-related variability, and the black birds are actually the older females.

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White-winged Scoter, adult female.

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White-winged Scoter, adult female: note the squarish shape of the wing coverts.

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White-winged Scoter, adult female.

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White-winged Scoter, female: dark below, slight bill bump, apparent bright feet, not very uniform back feathers… not sure about the age, could this bird be an adult?

The black-plumaged individuals are sometimes identified as first-year males with an extensive first pre-formative moult, but I think this explanation can be safely ruled out 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 shown by most of these birds. Only when the formative moult is much more advanced, around late January/February, first-winter males look similar, although with a much dirtier plumage, often looking “patchy” and not as uniformly jet black.

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White-winged Scoter, two adult females with a first-year male (right).

The head shape of these birds actually recalls that of adult males, due to a squarish head with a flat crown, a straight (non-concave) forehead profile 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. Although the differences are sometimes subtle, I think these features are distinctive enough to allow separation 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:

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White-winged Scoter, adult females: variability in head and bill shape.

Note that some adult females present some diffuse pink “brush-strokes” at the bill tip, but the iris seems to be pretty dark in all the individuals (cf first winter males, see below).

First-year males

By late November, juveniles still look very fresh, and the pale velvet at the base of the bill often looks nicely neat. Around 40-50% show what seem to be signs of moult around the face, and a few males have already developed 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.

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White-winged Scoters, first-year male (left) and first winter female (right). In my opinion, many juveniles can be reliably sexed in the field on grounds of the head and bill shape. Note, on the back, another first year female (left) and first year male (right).

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White winged Scoter, first year birds. Sexing is definitely not always possible – this bird (center) looks intermediate, or perhaps on the female side?

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White-winged Scoter, first-year male: a nice bird still in completely juvenile plumage.

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White-winged Scoter, first-year male: gradual lightening of the iris, traces of moult around the face.

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White-winged Scoter, first-year male. This looks like a VERY advanced first year male.

Regarding the separation from Velvet, in addition to the head shape, the shape of the feathering at the base of 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 (presumed) first-year males:

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White-winged Scoter, first-year males: variation in head and bill shape.

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White-winged Scoter, first-year male. Interesting individual with a narrow bill, and relatively rounded shape of the feathering at the lower corner of the bill base.

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, below the nostril, a right angle:

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White-winged Scoter, first-year female.

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White-winged Scoter, first-year female.

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White-winged Scoter, first-year females. In a few juveniles, the pale spots merge, giving a striking appearance.

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White-winged Scoter, first-year female – convex and rounded head profile, similar to Velvet.

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White-winged Scoter, first-year female: variation in head and bill shape.

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!

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White-winged Scoter, first-year female, showing a rounded corner of the feathering at the bill base.

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White-winged Scoter, presumed first-year female.

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Holboell’s Red-necked Grebe

by Guillermo Rodríguez

The American/East Asian subspecies of Red-necked Grebe, P g holboelliii, has been observed in the WP with accepted records in the UK (a bird shot in Wester Ross in September 1925 and subsequently identified based on measurements), Spain (two winter records from Galicia in 1984 and 1987, which were identified in the field, although these records will likely be reviewed again in the near future by the Spanish Records Committee), Iceland (at least five), and single accepted records in Sweden and Norway, in addition to several other reports. Since they are quite common as wintering birds along the American Atlantic coast (where, for instance, Pacific Diver is scarce/rare), they should be expected to reach Europe regularly. But do they?

holboellii is known to be larger and darker, and to have more yellow in the bill than the nominate grisegena. According to Pyle (2008), the differences in size are likely to be significant enough to clinch the ID. For example, the wing length is 180-212mm in holboellii versus 153-188mm in grisegena, showing that there is limited size overlap. However, these differences would obviously require in-hand measurements for identification. It’s my understanding that separation of holboellii from grisegena is currently considered to be impossible under field conditions, and the validity of the pattern of yellow in the bill has also been questioned (because a few grisegena show yellow bills similar to holboellii). However, the longest-billed holboellii show impressive harpoon-like bills which, in my opinion, are clearly outside the range of variation of grisegena.

Another identification feature that’s not usually mentioned in the literature is the general body structure; holboellii is considerably more powerful, with a longer neck, a longer and stronger bill and a flatter forehead. The head often looks square rather than rounded (although it’s also important to consider the age-related variation of the head shape, since first-winter birds tend to show rounder heads in general). As a useful comparison, holboellii somewhat resembles Great Crested Grebe. The main problem is that structure is subject to interpretation, and any identification solely based on the jizz is usually disputable. Variability in body shape is also quite extensive, and in particular many American holboellii may look as small and delicate as European grisegena. On the other hand, the largest-billed grisegena are at the same time the biggest individuals, with a more powerful structure than average birds, altogether favouring the holboellii impression.

Still, I do think that the largest and most striking holboellii could be definitively identified in the field if one turns up in Europe. For instance, check out two examples of such extremely large birds here and here.

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Red-necked Grebe ssp. holboellii, first-winter, February 2014. New Jersey. Picture by Sam Galick.

Many first-winter holboellii show a striking pale iris, which forms a contrasting ring around the dark eye that is very obvious with close views. I don’t know the variation in grisegena well (any feedback is welcome!), but my impression is that it isn’t always so obvious; perhaps the iris is on average paler in holboellii?.

The structural differences are easily noticeable even in distant birds at sea:

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Red-necked Grebe ssp. holboellii, December 2015. Massachusetts. Picture by Guillermo Rodríguez.

Sadly not all individuals are so distinctive; for instance the bird below – although it still looks large and long-billed – is probably still consistent with grisegena.

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Red-necked Grebe ssp. holboellii, adult, December 2015. Massachusetts. Picture by Jeremy Coleman.

And actually many holboelli look much smaller, more delicate and round-headed:

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Red-necked Grebe ssp holboellii, December 2005. Massachusetts. Picture by Tom Murray.

As a rough estimate, I would say that on the east coast of the United States the proportion of birds that are 1) markedly large and powerful, 2) intermediate 3) small, grisegena-like is somewhere between 20-40-40(%) and 10-30-60(%). My impression from a winter trip to Korea is that Asian holboellii on average are even more obvious, but at the time I didn’t pay enough attention (see some examples from Japan here).

Some birds, particularly adults, are remarkably dark, especially on the flanks; in addition, the facial dark mask sometimes extends towards the cheek.

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Red-necked Grebe ssp. holboellii, adult, November 2012, Massachusetts. Picture by Christopher N. Ciccone.

A couple of birds from Spain

One obvious problem with using structural features for identification is that they are strongly affected by the posture and activity of the birds. Take a look at this (presumed) grisegena from northern Spain photographed on two different days. I have the impression that birds at sea tend to look more like holboellii than birds on calmer waters, such as estuaries, where they tend to look more like grisegena. Presumably this is because the latter are more relaxed, but it’s difficult to say.

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Red-necked Grebe ssp grisegena, February 2016. Cantabria, N Spain. Picture by Lander Zurikarai.

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Red-necked Grebe ssp grisegena, February 2016. Cantabria, N Spain. Picture by Jesus Menéndez.

The amount of yellow on the bill of this bird is similar to that shown on all the holboellii in previous photos, extending over the entire lower mandible and reaching the upper mandible up to the nostrils.

In March 2015, an interesting Red-necked Grebe was found in Galicia, northwest Spain. The bird was remarkably dark on flanks and cheek and presented a substantially long neck, strong structure, and powerful bill, which accentuated its long-headed impression. This bird was probably within the size range of grisegena (at least it wasn’t one of the obvious and “identifiable” holboellii) and the reduced yellow in the bill was certainly against it being holboellii, but it still gave a Nearctic impression.

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Red-necked Grebe, first winter, March 2015. Galicia, N Spain. Picture by Jose Luis Lorenzo Garcia “Colon”.

Juvenile Semipalmated Plovers: variability of key features

by Guillermo Rodríguez

Semipalmated Plover is arguably one of the rarest nearctic shorebirds in Europe, although it has been suggested that its rarity is partly due to the challenge of separating it from Common Ringed Plover. The key identification features, such as the bill shape and the presence of white in the gape, are widely known and well described in several papers and field guides – so nothing new here – but I thought it would be interesting to take a detailed look at the variability of these characters for an identification refresher!

Let’s start with a couple of classic juvenile Semipalmated Plovers to illustrate the typical features. On these birds, note the:

– white above the gape

– yellow orbital ring

– generally delicate structure, with a very narrow rear part of the body

– small, rounded head

– relatively narrow and unbroken breast band of homogeneous width

– short, stout bill with a broad base and a typical triangular shape

– orangish to reddish patch at the base of the bill

– pattern of the upperparts with a broad pale fringe on the feathers of the wing coverts, which contrast with the scapulars and mantle where the feathers have a narrower pale fringe and a dark subterminal line, giving a tricolored appearance (a Cackling Goose-like feather pattern)

– and, of course, the semipalmation.

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Semipalmated Plover, juvenile. October 2016. Massachusetts. Guillermo Rodríguez.

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Semipalmated Plover, juvenile. October 2016. Massachusetts. Guillermo Rodríguez.

Variability of key features

Keep in mind that these are all juveniles! Photographed in Massachusetts, September/October, 2016.

White gape: this feature, first noted by Killian Mularney, is extremely reliable. Typically there are two main facial patterns: one in which the dark cheek patch merges with the dark lore line, forming a sharp angle (the “very obvious white gape” type); and the other in which the cheek patch directly touches the bill, but only the upper mandible, forming a small vertical white band surrounding the gape. In the second case, the dark cheek patch approaches the bill at an angle, whereas in Common Ringed it tends to look more horizontal. Practically all Semipalmateds present some white in the gape; however, in around 15% of birds the amount of white is limited or can look dirty, so that it isn’t very obvious and often requires a close inspection. Birds with truly dark gapes are quite rare and they might represent around 1% of the total (see below for an example); even in these birds the brown patch touches the bill at the matching point between the upper and mandible, but never (or at least extremely rarely) touching the lower mandible. It is important to bear in mind that some Common Ringeds do show a similar white gape, as Dani explained in this BF post a couple of years ago.

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Bill: this feature is quite variable, although it’s true that most birds present a stout, short bill, with a broad base, which often creates a concave upper contour to the bill. Nevertheless, in many birds it doesn’t look noticeably different from Common Ringed at a distance, and a few individuals show bills that would be quite typical for Common Ringed. The proportion of birds with an orangish to reddish patch at the bill base is very high, c.90%, and in many birds the patch extends to the bottom of the upper mandible.

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Orbital ring: this is another feature which is quite consistent and shows limited overlap with Common Ringed. Most Semipalmateds present a fine but obvious yellow orbital ring, which usually looks bright in direct sunlight. The number of birds in which the eyering looks dirty or darkish (and thus similar to the brightest eyerings of Common Ringed) is low. In the compilation below I show some examples of the darkest end of the range of variation.

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Semipalmation: contrary to what the literature usually states, I think this character is quite variable and perhaps even overlapping somewhat with Common Ringed – or at least, in some birds the difference cannot be assessed in field conditions. Roughly, the semipalmation between the middle and inner toes is very obvious in around 50-60% of birds. But with other individuals, I have had a hard time finding the semipalmation even when observing from only a few meters away, since they show just a minute piece of skin, very similar to the hint of semipalmation that some Common Ringed show. The plate below depicts birds with minimal, moderate, and obvious semipalmations, respectively, from left to right.

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Breast band: this is another highly variable character, as shown below, with many birds showing a very fine band or simply a narrow line in the middle of the breast, and others showing an unbroken broad band of uniform width or even a band with two deep rounded patches on each side of the breast, similar to Common Ringed. Instead of shape, I’d highlight two different aspects of the breast band: (I) the colour, which is typically brownish in Semipalmated, and is often concolorous with (or only slightly darker than) the back, only rarely showing the really blackish tones that are common in Common Ringed; and (II) the “density”, as in Semipalmated the band is uniformly densely coloured and the dark-white transition is sharp, creating a well-defined band contour. In many Common Ringed, the feather tips in the band show some whitish fringes, leading to a kind of diffuse pale barring, and the dark-white transition at the centre of the breast (where the band is broken) is more diffuse.

montaje_pechos

Wing bar: the wing bar is known to be a supporting character, with Common Ringed showing broader and longer white bars than Semipalmated. On average there is a difference, but the overlap seems to be considerable (especially with some Common Ringed that showing short bars). Typically the difference is found on the inner primaries, where the bar is narrower in Semipalmated.

montaje_wingbars

From left to right, three Semipalmateds and a Common Ringed (picture by Pablo Gutierrez) for comparison.

Tail pattern: usually not described in the literature, I find this feature slightly more reliable than the wing bar. In both species the innermost pair of rectrices is dark and the outermost is white, with increasingly large white tips from t2 to t5. The size of the white tip, particularly in t2 and to a lesser extent in t3, is much smaller in Semipalmated, so that the total amount of white in the tail is less. In Common Ringed, the increase in white on the feather tip from t1 outwards looks more gradual. However, this feature is usually unnecessary, as pretty much every time you see the bird spread its tail it has also called!

colas

Bottom left picture shows a Common Ringed for comparison (picture by Pablo Gutierrez).

General coloration: most records of Common Ringed Plover in the States highlight how pale they are above compared to Semipalmated. I don’t find Semipalmated strikingly dark, so perhaps the difference is only obvious with side-by-side comparisons (or it could be due to plumage variability of Greenland birds, supposedly the ones that reach the States).

Some difficult birds

It’s time to take a closer look at a few examples of birds in which some of the features are (at least partially) missing:

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 This bird completely lacks white in the gape, and the bill is relatively slender and longish. It does present other typical features such as a bright orbital ring, red at the base of the bill reaching the bottom of the upper mandible, a uniform breast band roughly concolorous with the back, and a typical pattern to the upperparts.

4

This bird shows a somewhat narrow and long bill, limited white in gape and bulky structure. Again, the eyering, red patch at the base of the bill and breast band are quite typical.

5

The reduced and dirty white above the gape, all black bill and Common Ringed-like breast band make this individual slightly confusing, but the presence of the eyering and the bill shape are quite diagnostic. The pale fringing in the crown is also more typical of Common Ringed, but quite variable.

6

 This is one of the most Common Ringed-like Semipalmated Plovers I’ve seen; the size and shape of the bill, pronounced and blackish breast band, and apparently dark gape are all quite reminiscent of Common Ringed, and likewise, the eyering is likely within the species’ range of variation.

These are likely the most “conflictive” birds I’ve seen during the 2016 autumn migration in the States, out of several hundred birds studied. Therefore, the combination of white gape, consistent eyering and stout bill seems to apply to the vast majority of birds, and it’s very rare that the three characters are lacking on the same individual.

Check out, for comparison, these juvenile Common Ringed Plovers from Spain:

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Common Ringed Plover, juvenile, Galicia, Spain, October 2015. Pablo Gutierrez.

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Common Ringer Plover, juvenile, Madrid (Spain), September 2015. Miguel Angel Serrano Rubio.

This last Common Ringed is partially reminiscent of Semipalmated, with its delicate structure, stout bill, and marked upperparts. However, the dark gape, lack of yellow eyering, and the blackish, broken and less dense/diffusely barred breast band easily clinch the ID.

First year Hudsonian Dunlin

By Guillermo Rodríguez

Hudsonian Dunlin (C a hudsonia) records have been claimed several times in the UK & other countries in Europe, usually adults in mostly summer plumage in late spring and summer, when the pale head and bright back of Hudsonian is quite different from European birds (but, on the other hand, is difficult to separate from several Pacific taxa). However, Hudsonian Dunlin also differs from Dunlins that occur regularly in Europe (alpina/schinzii/arctica) in juvenile/first-winter plumage, when the likelihood of a vagrant is perhaps higher. Dunlins arrive in good numbers to the east coast of the United States in late September, only slightly later than Baird’s Sandpiper and American Golden Plover.

After careful study of a few hundred first-winter birds, I think some of the features typically shown by Hudsonian are relatively rare in European birds, and their combination on a prototypical individual might indicate a nearctic origin.

Moult: probably the most obvious and eye-catching difference at first glance (in September/early October) is that the birds arrive from the breeding grounds already in a remarkably advanced moult. Most birds have moulted head, breast, and most of the back feathers; the belly, rump and wing coverts are usually moulted slightly later. For instance, all 9 first-year birds seen in Massachusetts on September 24th were in moulted plumage; only one out of 76 was still in mainly juvenile plumage on October 1st; and only 3 out of 54 seen on October 8th showed partially (but still fairly advanced) juvenile plumage. Thus, the proportion of birds arriving with retained juvenile plumage may be well below 5%. At this time of year, most first-year Dunlins in Europe have some replaced scapulars, but usually not most of them and rarely if ever show a complete winter plumage overall (ie also including head, mantle and breast). Some Hudsonian Dunlins leave some back and rump feathers unmoulted until the late autumn and winter, showing a characteristic line of conspicuous rufous-fringed scapulars contrasting with the moulted greyer feathers, reminding in some way first-year Western Sandpiper.

Bill shape: Hudsonian Dunlins on the East Coast present limited variability in bill shape and length, at least compared to Dunlin taxa in other parts of the world. Most Hudsonians have a long bill, which curves down at the end, somewhat similar to Curlew Sandpiper. Some birds also show a sort of ‘drop’ at the bill tip. Even in the shortest-billed birds the bill shape is characteristic, and considerably different from the majority of Dunlins in Europe (although, obviously, European birds sometimes show similar bills).

Facial pattern: many Hudsonians present a characteristic facial expression: the brow is usually broad, and ends sharply just beyond the eye; in some birds there is a conspicuous pale area in front of the eye. The cap and nape are roughly concolorous, and thus more contrasting with the supercilium. In European Dunlins, the nape tends to be paler and so the supercilium seems to “merge” with it, contrasting with a slightly darker cap. As a useful comparison, these differences are reminiscent of the differences in facial pattern between juvenile Western and Semipalmated Sandpipers (with Hudsonian being more similar to Western).

Breast and flanks patterning: this feature has been considered as diagnostic in the past. Once they have moulted into winter plumage (but generally not in juvenile plumage!), around 70% of birds present sparse short streaks on the flanks of the underparts, beginning at the breast and sometimes reaching as far as the undertail. In most of these birds, the dirty grey patch on the breast partially extends towards the belly along the flanks. In most European birds, the underparts are neatly white, but some exceptional birds might show a similar streaked pattern to Hudsonian.

Some examples illustrating the variability of first year Hudsonian Dunlins.

1

Hudsonian Dunlin, first year, September 21, 2016. Massachusetts. Guillermo Rodríguez.

2

Hudsonian Dunlin, first year, September 24, 2016. Massachusetts. Guillermo Rodríguez.

3

Hudsonian Dunlin, first year, October 8, 2016. Massachusetts. Guillermo Rodríguez.

4

Hudsonian Dunlin, first year, October 8, 2016. Massachusetts. Guillermo Rodríguez.

Even in the shortest-billed individuals the bill drops down at the tip. Note also the characteristic pattern of the supercilium.

5

Hudsonian Dunlin, first year, October 8, 2016. Massachusetts. Guillermo Rodríguez.

6

Hudsonian Dunlin, first year, October 8, 2016. Massachusetts. Guillermo Rodríguez.

9

Hudsonian Dunlin, first year, October 8, 2016. Massachusetts. Guillermo Rodríguez.

8

Hudsonian Dunlins, October 8, 2016. Massachusetts. Guillermo Rodríguez.

Note the similar bill shape and size in most individuals. Variability is relatively limited in the East Coast!

For comparison, look at this typical Dunlin from N Spain, still in mainly juvenile plumage in September:

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Dunlin, first year, Galicia, N Spain, September 15. Photographer: Pablo Gutierrez.

and a slightly more advanced bird (October), with extensive replacement on mantle and scapulars but still retaining juvenile head and breast feathers.

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Dunlin, first year, Galicia, N Spain, October 3. Photographer: Pablo Gutierrez.

Finally, check out this individual from the Canary Islands, identified as a (potential) Hudsonian on grounds of the flank streaking. The Spanish RC studied and eventually rejected this record. I think the bill does not look particularly good and the breast is too neat for Hudsonian, but undoubtedly a difficult bird!