Unprecedented spring arrival of Greenland Dunlin ssp. arctica to Northern Spain and a first approach to its identification

The population of Dunlin breeding in a remote area of NE Greenland belongs to the poorly-known subspecies arctica, the so-called Greenland Dunlin Calidris alpina arctica. It is an endangered subspecies, and it has received little attention in the literature despite it probably being one of the most distinctive Dunlin subspecies. Greenland Dunlins spend the winter in NW Africa, and some are recorded in both spring and autumn migrations along the Atlantic coast of the UK, Spain, Portugal and especially Ireland, but in general we do not have a very clear picture about their migratory routes and identification.

Between early May and early June 2022 we witnessed a fantastic and unprecedented arrival of Greenland Dunlins ssp. arctica along the Northern coast of Spain, possibly due to the prevalence of strong NE winds, that usually force shorebirds to stop in Iberia during the spring northbound migration. Sightings of 2-5 birds on a daily basis were regular at several traditional shorebird stop-over sites, counting up to 20-25 birds together during peak days. We have recorded Greenland Dunlins in N Spain annually on both passages over the last few years, but always in very small numbers compared to this year’s relatively large numbers, so we are not sure what exactly happened this year. The Southern Dunlin (ssp. schinzii) is the default taxon during migration in N Spain (which overwinters further south in NW Africa), with some (western) ssp. alpina -that overwinter here in small numbers- remaining in spring, mostly 2cy birds. 

There is surprisingly little information about Greenland Dunlin in the literature -especially given how distinctive this taxon can be-, with few pictures published. Martin Garner wrote a post dealing with the subject, highlighting the main identification features. This post, along with some inspirational and educational email exchange on the subject with Dunlin (and everything else) expert Killian Mullarney, was our starting point in the process of understanding arctica. This spring brought us the opportunity to study in detail and photograph many arctica, gathering a nice collection of pictures that hopefully will help to illustrate the main plumage and structural features characteristic of arctica.

The present post aims to put arctica on the spotlight and raise awareness about it. We will describe the main features based on our experience, and show some examples of typical arctica seen this past spring in N Spain. Note however that the most striking birds may only represent a proportion of the entire arctica population, and it is also unclear whether intergrade populations exist or not, so studies digging deeper on the subject are clearly required to fully understand both the individual and geographical variation. We will discuss some not so obvious birds to complete this first approach to the separation of arctica and schinzii, but please take this as work in progress!

In addition we have compiled a photogallery with many examples of arctica, so birders can get a wider understanding about the variation within our arctica. Check it out here!

Identification key to the separation of Greenland Dunlin Calidris alpina arctica and Southern Dunlin Calidris alpina schinzii (c) Marti Franch, Guillermo Rodríguez & Daniel López-Velasco. The plate shows classic birds of each taxon, but there is considerable individual variation and most features overlap – see the main text for a detailed description.

Greenland Dunlin ssp arctica: key features

Classic breeding-plumaged Greenland Dunlins ssp. arctica in May-June are often extremely eye-catchig in the field –but beware, sometimes less so in photos!- if seen within a flock of schinzii due to their smaller size and very pale overall plumage. Interestingly, sometimes arctica seem to stick together and move on their own, together in small flocks, away from schinzii. Their overall paleness is due to the grey or even whitish fringes of most of the upperpart feathers, as opposed to the much more vivid coloured schinzii in which most feathers are orange or buff-fringed. However, larger and/or more brighter coloured arctica exist, -and might actually account for a larger percentage than previously thought-, and can easily go unnoticed. There are quite a few other plumage differences that consistently differ between both taxa and, if all combined, make some breeding-plumaged arctica fully identifiable in the field, beyond  “presumed arctica” or “arctica candidates”, as we will show below.

Based on our experience, the key features when comparing with ssp. schinzii are as follows:

• Structure: arctica tends to be smaller than schinzii, sometimes strikingly so, almost Little Stint-like, but there is some overlap and not all birds are that eye-catching in terms of size (especially females). Most also show a noticeably shorter bill, with a slightly dropping tip, but it´s important to note that we have also seen several presumed female arctica with bills as long as schinzii. Structurally they often look elongated, with a narrow rear part of the body, created by a longer primary projection often emphasized by their usual behaviour of staying in a more horizontal position than other Dunlins. This all adds up to create quite an striking jizz that, which combined with their overall greyer plumage, can lead to a look reminiscent of a White-rumped Calidris fuscicollis, Baird’s Calidris bairdii or even Western Sandpiper Calidris mauri (depending on the individual). Be prepared for a moment of shock and almost disbelief when you bump into your first arctica while scanning a Dunlin flock, especially if you do not see the black belly patch!

• Breast pattern and belly patch: in arctica, the spotting on the breast pattern consists of sparse, thin and very small spots that typically do not reach the belly patch, thus sometimes a clean “white band” just above the belly patch is visible. In schinzii these breast spots tend to be triangular, “dirtier” and larger, merging into the belly patch. The belly patch varies in size but on average in arctica is rather small, sometimes almost absent, looks “blotchy” and It is actually often formed by several large spots, instead of it being a single, uniform-looking, large and thick patch as is often the case in schinzii. Furthermore, the white flecking or peppering on the dark belly patch is usually very obvious in spring in arctica, and is one of the first things that attracts attention when the birds are roosting and facing the observer, thus not revealing the upperparts pattern. Although these differences are pretty solid amongst classic birds of both subspecies, there is considerable individual variation and some schinzii –especially males– may show underparts that can be very similar to arctica (and also be aware of incomplete moults and 2cy schinzii / alpina, which can usually be told apart by a number of other features).

• Mantle and upper scapulars: perhaps the most reliable feature to identify “less classic arctica”, but there is still quite variation and overlap. In schinzii, the black centres of the upper scapulars are broader and longer, usually reaching the feather tip, and tend to show a rectangular or spade-like shape. The fringes are typically orange/rufous or bright buffy. In arctica, the tip of the dark center is usually restricted to the inner part of the feather and typically has a pointed tip – overall resembling the well-known pattern shown by Blyth’s Pipit in the median coverts (MCs)-. In some scapulars there is a fine dark line running along the shaft. The rest of the feather is often pale grey, sometimes yellowish and even whitish, and especially if it has little black on the centre, it can be easily mistaken as an alternate (winter-type) feather if not analyzed in detail. Some/most of the mantle feathers in the most classic examples of arctica have very pale edges that can look bright white, especially at a distance, strongly contrasting with the black centres, and giving the back a very striking “frosty” look. This pattern can also form striking “braces” in the back, almost resembling those of a juvenile Little Stint Calidris minuta. Due to this characteristic and striking pattern, if seen from behind Greenland Dunlins can sometimes be confused with Sanderling Calidris alba! They may be quite some overlap though, and arctica with a mix of grey and orange feathers are not rare, and we have even seen a few birds with some deep rusty feathers (a colour tone similar to that typical of the Eastern Dunlin forms). Conversely, Southern schinzii with typical arctica-like scapulars and coverts also exist, although the proportion of such birds is unknown.

Comparison between mantle and upper scapulars of Greenland arctica (top) and Southern schinzii (bottom) Dunlins. Note the long, rectangular-shaped dark centres in schinzii that almost extend to the feather tip; the dark centres are more restricted in arctica, showing a different shape and are often combined with a thin dark shaft. Note too how pale grey/whitish some of the fringes are.

• Lower scapulars: in schinzii the black often encloses a pale patch or shows a variegated pattern. arctica rarely shows this pattern; usually the black is restricted to the inner part of the feather, and they often show a distinctive asymmetric pattern in which the inner web is almost entirely grey, whereas in the outer web the black extends further and the shaft is dark (see some examples below). As with the previous feature, expect some overlap so do not take it as a fully diagnostic trait!

Comparison between the lower scapulars of Greenland arctica (top) and Southern schinzii (bottom) Dunlins. Note the characteristic variegated pattern of schinzii with pale spots enclosed within the dark tongue, rarely shown by arctica. Note too the simple, rather uniform grey pattern of some of the feathers in arctica.

• Head pattern: sides of head, ground color of the crown, nape and face tend to be much paler in classic arctica, compared to schinzii, and this can be quite striking at a distance. However, there is variation on these features, with some arctica showing darker heads and some schinzii having paler than usual patterns.

• Moult: we have not seen a consistent difference in moult between arctica and schinzii, but we have seen quite a few arctica with prenuptial moults including wing coverts, something not common in schinzii. It is thus quite possible that arctica performs on average more extensive moults than schinzii -- something typical of shorebirds breeding at high latitudes – but a more systematic study would be required to properly address statistical differences in moult.

Let’s now check some examples in order to understand the variation and key features (in particular the distinctive pattern of the upperparts).

Some examples of classic Greenland Dunlin ssp. arctica

Typical arctica are striking and in our opinion can be confidently identified even out of range, if they show the combination of features described above. It should be noted that we might be sex-biased, positively identifying as arctica mostly males, as they tend to be smaller, paler and more contrasted –and thus differing from the average schinzii- than the females in all Dunlin subspecies.

Greenland Dunlin C. a. arctica (Spain, May 2022) (c) Daniel López-Velasco. A classic individual in all features – this bird almost resembles a Western Sandpiper Calidris mauri!-.

Greenland Dunlin C. a. arctica (Spain, June 2022) (c) Guillermo Rodríguez. A particularly grey individual, note also the classic “white band” just above the belly patch formed by the absence of breast spotting. Imagine that we erase the dark belly patch from this image – wouldn´t it look a bit like a Western/Semipalmated Sandpiper Calidris pusilla/mauri?

Greenland Dunlin C. a. arctica (Spain, May 2022) (c) Daniel López-Velasco. Another extreme, very frosty-looking bird that should not pose any identification problems.

Greenland Dunlin C. a. Arctica, top and bottom (Spain, May 2022) (c) Daniel López-Velasco. A particularly pale and striking individual, almost lacking any dark in the belly patch. General impression is somehow intermediate between Western Calidris mauri and White-rumped Sandpipers Calidris fuscicollis. Note too this bird has some rusty-fringed upper scapulars. When seen in flight, from above, it could easily be mistaken for a male Western!

Greenland Dunlin C. a. arctica (Spain, May 2022) (c) Guillermo Rodríguez. A bird with more contrasting breast spotting but showing other typical features, including mantle and wing feathers. Typical horizontal stance emphasized by the long rear part of the body.

Greenland Dunlin C. a. arctica –front, left bird- with Southern Dunlins C.a. schinzii (Spain, May 2022) (c) Guillermo Rodríguez. When seen alongside schinzii, arctica usually looks paler, smaller and more slender.

Greenland Dunlin C. a. arctica, right bird, with Southern Dunlins C.a.schinzii (Spain, May 2022) (c) Daniel López-Velasco. The most classic individuals are quite eye-catching when seen within a group of schinzii.

 Greenland Dunlin C. a. arctica with Tundra Ringed Plovers Charadrius hiaticula tundrae/psammodroma (Spain, May 2022) (c) Guillermo Rodríguez.

Greenland Dunlin C. a. arctica, right bird, alongside a similar-sized Little Stint Calidris minuta (Spain, May 2022) (c) Daniel López-Velasco.

Greenland Dunlin C. a. arctica (Spain, May 2022) (c) Daniel López-Velasco.

Some examples of typical Southern Dunlin ssp. schinzii

Below we show some representative examples of ssp schinzii seen during the spring passage in Spain; based on ringing recoveries most of the schinzii population migrates along the Iberian Atlantic coast.

Southern Dunlin C.a.schinzii (Spain, June 2022) (c) Guillermo Rodríguez. A classic schinzii with orange-ish upperparts with long black tongues, large belly-patch and dense breast spotting.

Southern Dunlin C.a.schinzii (Spain, June 2022) (c) Guillermo Rodríguez. Likely a female based on spotted throat, lack of contrasted collar and long bill.

Southern Dunlin C.a.schinzii (Spain, May 2022) (c) Guillermo Rodríguez. A slightly less colorful schinzii; note the presence of two grey lower scapulars on this bird, although still showing a different pattern from that typical of arctica.

Southern Dunlins C.a.schinzii  together with at least one Greenland Dunlin C.a.arctica, in the front (Spain, June 2022) (c) Guillermo Rodríguez. A group mostly formed by schinzii showing variation on upperparts colouration and size of belly patch.

(Presumed) Southern Dunlin C.a.schinzii (Spain, May 2022) (c) Guillermo Rodríguez. Not every small Dunlin is a Greenland Dunlin – this bird, likely a male, looks small and definitely short-billed. However, it shows typical schinzii upperpars, large belly patch and compact structure.

Southern Dunlins C.a.schinzii (Spain, May 2022) (c) Guillermo Rodríguez. Another example of a small, short-billed presumed schinzii that could be mistaken as arctica, emphasized here due to the direct comparison with more typical schinzii.

Some not so obvious presumed Greenland Dunlin ssp. arctica

Of course not all arctica are that distinctive and obviously some variation should be expected; here we depict some examples of more challenging birds that require deep analysis. Their identification is putative based on current knowledge. It is unclear whether birds from nearby populations (for instance Svalbard or the schinzii populations that are colonizing S Greenland; or even further south, Iceland/N Scotland) can look intermediate between classic arctica and schinzii or not.

Presumed Greenland Dunlin C.a. arctica (Spain, May 2022) (c) Guillermo Rodríguez. This bird looks bulky, relatively long-billed and with an extensive belly patch – note however typical pattern of upperpart feathers, with grey fringes, pointed dark shafts and completely grey lower scapulars with dark bases. Also note extensive moult including most wing coverts and tertials.

Presumed Greenland Dunlin C.a. arctica (Spain, May 2022) (c) Guillermo Rodríguez. A bird showing a rather large and uniform dark belly patch.

Presumed Greenland Dunlin C.a. arctica (Spain, May 2022) (c) Guillermo Rodríguez. Another example of a long-billed bird with a large belly patch, but the upperparts feathers clearly point towards arctica, as does the sparse breast spotting and elongated structure (perhaps not so obvious in this picture).

Presumed Greenland Dunlin C.a. arctica, right, with Southern Dunlin C.a. schinzii, left (Spain, May 2022) (c) Guillermo Rodríguez. This arctica is slightly larger than the schinzii, and shows some orange fringes on the upperparts, but all other features perfectly fit with arctica.

Presumed Greenland Dunlin C.a. arctica (Spain, May 2022) (c) Guillermo Rodríguez. Another brownish-looking presumed arctica that could possibly go unnoticed to the untrained eye.

Birds of uncertain identity

Our field experience mainly relies on observations of migratory birds so we hardly ever know the breeding origin of our Dunlins; this fact makes it really difficult to draw exact lines and define with certainty the range of variation of each taxon. Below are some examples of birds that we are simply unable to assign to subspecies level, although we believe they are most likely either variation within “pure” arctica from the core Greenland population or perhaps birds from nearby populations.

Unidentified Dunlin C. alpina ssp (Spain, June 2022) (c) Guillermo Rodríguez. This bird combines a rather grey colouration, typical arctica pattern on most upperpart feathers and a long rear end, but note that the belly patch is of considerable size and it shows large spots on the breast. We do not believe this is a schinzii from mainland Europe, but it is difficult to assess whether this falls within arctica variation from the core Greenland population or not.

Unidentified Dunlin C. alpina ssp (Spain, May 2022) (c) Guillermo Rodríguez. A most interesting bird, combining both schinzii and arctica features.

Unidentified Dunlin C. alpina ssp (Spain, June 2022) (c) Guillermo Rodríguez. This bird combines orange upperparts and a rather large belly patch together with typical arctica features such as scapular pattern. Note also extensive moult.

Unidentified Dunlin C. alpina ssp (Spain, June 2022) (c) Guillermo Rodríguez. A short-billed, rather pale bird with a large belly patch and dense spotting on the breast.

Acknowledgements

We would like to thank Marti Franch for preparing the main plate that illustrates this post and explains the differences between schinzii and arctica.