Sugar Cubes

text by Abu & Aki (aka Axel Bräunlich)

photos by Abu (© Andreas Buchheim)

We get a lot of requests for help in the identification (ID) of redpolls photographed in Mongolia. This clearly illustrates that their ID is not as easy as some field guides may suggest. As a consequence, our present post is intended as a kind of ID-aid for those who know even less than we do. None of us would ever claim to be an expert in redpoll ID, so if you find errors please don’t hesitate to comment!

It is generally acknowledged that two species of redpoll occur in Mongolia. The first is the common Mealy Redpoll, formerly called Common Redpoll, Carduelis flammea. We regard the latter name as inadequate as it has been traditionally used for Carduelis flammea sensu lato [in a wider sense] and its continued use will cause unnecessary confusion as it will remain totally unclear which taxon is, or which taxa are called “Common Redpoll”. The second is the rarer Arctic Redpoll (or Hoary Redpoll) Carduelis hornemanni, with subspecies C. h. exilipes (this ssp is sometimes called Coues’s Redpoll) occurring in the country.

Separating the two species, which freely mix in wintering flocks, is known to be not always easy, with some individuals being even not identifiable in the hand. This post deals with the field ID only, based on plumage and structure. One reason for this is that most birders will see the birds in field only (there are not many ringers in Mongolia), and the other reason is our lack of in-hand material. Anyway, we will reiterate a lot of facts written by others, but as soon as we get a sufficient number of both species in hand we will come back to this problem. Voice is not discussed here—this would go beyond the scope of the post. However, if you are interested in voice, here are some links to check:

“Common” Redpoll on xeno-canto
Arctic Redpoll on xeno-canto
Redpoll Chatter Calls, useful for identification? (Birding Frontiers)
some stuff from America (Earbirding)

All the photos in this post have been taken either on 18 December 2013 (photos 1-8, 13-17 and 27-29) or on 12 January 2014 (9-12, 18-26 and 30-32) below Songino Khairkhan Uul near Ulaanbaatar (for more obs from this site write “Songino” in the field “search this blog” on top of the side-bar). They are not at all a representative sample of the up to approximately 180 redpolls which had been present, since the main photographic focus was on Arctic Redpoll.


Status in Mongolia

Both species are more common in the north of the country than in the south. Mealy Redpoll is a very common winter visitor, with strongly varying numbers between different winters. In the Ulaanbaatar area, there had been almost no records during the winters of 2011/12 and 2012/13, but the region was literally flooded by them during the winters of 2008/09 and 2010/11. Additionally, it is breeding in the forests of central and northern Mongolia (Abu pers. obs.). Arctic Redpoll has been recorded only during winter. It is unfortunately not exactly known when the first birds arrive and the last depart. Their numbers in relation to Mealy Redpoll are not exactly known but Arctic is always(?) the rarer of the two. For example, in Khovd, at the foot of the Mongolian Altai in western Mongolia, Aki recorded 70 redpolls between late October 2005 and late November 2007. 59 were Mealy, 2 Arctic, and 9 remained unidentified. There is usually never enough time to go through all birds of the larger flocks to check for Arctic Redpolls, so it is almost not possible to get a correct estimate of the proportion of the rarer species.

The situation is probably a bit similar in other areas of Central and Eastern Asia. Beijing, for example, only has two records of Arctic (one pre-1950 and one this winter found by Paul Holt in a flock of 40+ Common). It is suspected that many are missed, but redpolls are generally uncommon winter visitors. This winter something of an influx had been reported, with flocks of up to 100+ Mealy reported, but that is exceptional (Terry Townshend of Birding Beijing pers. comm.). To the west of Mongolia, in Kazakhstan, Mealy is a rare resident and/or breeding migrant, rare passage migrant and common winter visitor, whereas Arctic has been reliably recorded only once (Dec 2011; The Birds of Kazakhstan).


General impression

Both species are rather small finches with a bouncing, erratic flight and can occur in quite large flocks, often comprising several hundred individuals. Their ground colouration is quite pale with a variable amount of streaking, in Mongolia only matched by “Pale Mountain” Twite Carduelis flavirostris altaica and Rock Sparrow Petronia petronia. The latter species differs structurally from either of the redpolls. Their name-giving red poll (poll = the top or back of the head) is found in almost all individuals, but very few may lack it completely. The poll can show any colour between carmine red and yellow, so be prepared!


Moult and feather wear

When having completed their moult after the breeding season all redpolls possess a fresh plumage which is the palest plumage they get during the course of the year. Birds hatched undergo a partial moult and are also rather pale. Not much is known about the moult of Arctic, though. Through the effects of wear the redpoll plumage gets darker and darker until the onset of the next complete moult. This is because all fresh feathers have pale buffish tips concealing the darker parts. The pale tips slowly wear off, resulting in the darker parts becoming exposed. This applies to all feathers, and thus, for example, the breast of adult males gets pinker AND the flanks will show more dark streaks (very often fusing into two long dark streaks) AND the mantle will become darker. In this context it is most important to know that the rump also will show more streaking in spring and summer, rendering a correct ID even more difficult.


ID criteria

In a way these little birds are the “large white-headed gulls” among the songbirds, with all field marks showing a certain degree of variation and overlap between the members of this tricky species pair. Hence their ID requires checking as many characters as possible and even then some birds must be left unidentified, just as in the aforementioned group of gulls. In this respect it would be very useful to take as many photographs as possible when coming along redpolls in Mongolia. With digital photography, taking a large number of images isn’t a cost factor anymore, and often some features (like undertail-covert details) are only revealed when checking photos on the computer screen later on.

The following criteria had been put on the table by various authors, namely Lewington et al. (1991), Svensson (1992) and Jännes (1995).

Let’s start with the most important criteria:

Pattern on the longest undertail-coverts
Observers should make sure that they are looking at the right feathers, as the longest undertail-coverts (a pair of feathers) should be checked first. The undertail-coverts are mainly white but the longest usually show a dark grey central streak (quite pointed) along the feathers’ shaft. If this is lacking you are very likely looking at an Arctic. Unfortunately, some Mealy can lack this dark streak as well, but it is said that unstreaked undertail-coverts can be found in adult male Mealy only. However, these adult male Mealy should be recognizable as such by other features and should cause no further problems. Most Arctic have this shaft streak, but it is very, very narrow and should not measure more than 2 mm (OK, this is hard to check in field, we admit). If the streak is very wide, i.e. more than 2 mm, then you most probably have a Mealy sitting in front of you. But all intermediate birds require extra care as these intermediate patterns can occur in both species. The wider variety occurs more often in Mealy, and undertail-coverts tending towards the narrower end are shown more often by Arctic. Nevertheless, we could not trace a photo of an Arctic showing streaks on more than the longest undertail-coverts, hence we carefully suggest that those birds with streaks on more than the longest undertail-coverts should be Mealy (but more work is required on this).

Rump pattern
Adult males of both species can show a square unmarked white area on their rump, the so-called “sugar cube”. This cube will be on average larger in adult Arctic, but there is some overlap. Non-adult male Mealy usually don’t show such a sugar cube and have the rump streaked along its length from the back to the uppertail-coverts, the latter being similar (dark) in both species. Following Svensson, this sugar cube should cover a minimum of about 10 mm in Arctic, but Jännes mentioned first winter birds showing even less than this. On photographs it is possible to make a realistic estimate of the dimension of the sugar cube. This is because the primary projection (the distance between the tip of the tertial feathers and the tip of the primary feathers) of redpolls measures about 20 mm (own data). Although only Mealy had been measured, we assume that the primary projection is similar in Arctic as both species have the very same wing length and show an apparent similar primary projection in the field. Hence this can be used for an estimation, but this is limited to photos which show the birds from the side! Birds with smaller sugar cubes cannot be safely identified by this feature alone and observers should check other criteria. Note that streaking gets more obvious by wear, thus it will be much more difficult to judge this feature from spring through the summer until the next complete moult.

Amount of breast side and flank streaking
Arctic usually shows the strongest (but still weaker than in an average Mealy) streaking on the breast sides and this is levelling off down the flanks, often leaving the rear flanks unstreaked. If streaks are present on the rear flanks they should be sharply defined and rather narrow (again narrower than in average Mealy). In Mealy very often the streaks become more pronounced towards the rear flanks, and some birds can show them almost as strong as in a Red-throated Pipit Anthus cervinus, but the streaks will not show as clear (being a bit “blurry”). Birds without rear flank-streaking should be Arctic. The difference is most obvious when dealt with adult males and when the birds are in fresh plumage (autumn and winter).

Other criteria should be considered supportive only:

Facial pattern
Again, the difference between the twin species is most pronounced in adult males and also when they have a rather fresh plumage. Arctic can lack the streaks on the sides of the head almost completely. They also should show ear-coverts that are not much set apart from the rest of the head, being quite uniformly coloured, and having no dark rear. There are, of course, some heavily streaked Arctic which do NOT differ from the average Mealy in this feature, so be careful.

Colouration of the throat and lower cheeks
Very often Arctic are creamy ochre here, but some Mealy show this as well, so this colouration should be considered as a supportive feature only.

Bill length
Svensson gives a bill length of 7.0-9.6 mm for Arctic and 7.2-10.4 mm for Mealy. This means that only those birds with the shortest bills can safely be identified as Arctic and those with the longest likewise as Mealy, but the overlap is huge, thus most individuals not only fall within the range of overlap, but it will prove to be a very tough job to “measure” the bill in field! The bill length can only (almost reliably) judged from photographs with the bird facing to the side, at an angle of 90° to the photographer. Otherwise photos can be quite misleading in this respect.

Nasal feathering
The longer nasal feathering contributes to the short-billed appearance of Arctic but as there is a lot of variation only extremes can be identified by this.

Colour of the wingbar
The inner greater (secondary) coverts of all redpolls have mostly white tips which are contrasting to the rest of the feathers, forming a wingbar. The tips of the outer greater coverts of Mealy are off-white to orangey buff whereas those of Arctic are said to be as white as the inner ones. Whether this applies to all age classes and sexes and whether this holds true for the whole year we do not know.

Fluffiness of the belly feathers
As Arctic are showing up in Mongolia when temperatures can plummet down to minus 45°C, they will fluff out all the feathers they got and this is exactly that what all other birds will do, too. Thus this anyway minor feature is useless.


Gallery

Adult male Arctic Redpoll

The following four photos (1-4) show an adult male Arctic. Note how outstandingly pale those can be. The pale pink on the bird’s breast is just visible but it should become more obvious during the next months as the pale feather tips will wear off. The faint flank streaking adds to the overall pale appearance. On the second photo only a very indistinct shaft streak shows on the longest undertail-coverts, and the unstreaked white part on the rump seems to reach up to the back (between the tertials), but this cannot actually not judged with certainty from this photo. The third photo shows the bird closer up. It is quite short-billed and does not show much streaking on the creamy head. The wingbar is not pure white, though. In photo 4 the almost complete white undertail-coverts are clearly visible (on the longest undertail-coverts an easy-to-overlook shaft streak is present) as is the sugar cube (but its size cannot be estimated from this angle!).

1. Adult male Arctic Redpoll

2. Adult male Arctic Redpoll

3. Adult male Arctic Redpoll

4. Adult male Arctic Redpoll

Adult male Mealy Redpoll

The next are two photos (5 & 6) show adult male Mealy (different individuals). Note the intense pink colouration already present in early winter (it will get even more intense), the longish bill, compare the amount of streaking on the (rear) flanks, the ear-coverts and head with that of the Arctic above. The wingbar of the bird in photo 6 darkens outwards.

5. Adult male Mealy Redpoll

6. Adult male Mealy Redpoll

The following three Arctic show the typical creamy ochre throat and lower cheeks and we wonder whether this is shown only by (first winter) males. The composite photo 7 shows the same individual from two different sides. Note the very pointed tail feathers which are juvenile—thus this is a first winter Arctic. Take a look at its pale, almost unstreaked head, the limited amount of flank streaking (but reaching quite far back here), the all-white wingbar, and note that the sugar cube reaches high up to the tip of the shortest tertial. In field it was established that the longest undertail-coverts (here obscured) were completely white.

7. First winter Arctic Redpoll

Next (8) comes another fine example of an easy-to-identify Arctic with rather limited flank streaking, short-billed appearance, plain head (here the supercilium meets over the bill to separate the poll from the black forehead, this is not uncommon in Arctic but does occur in Mealy as well) and the sugar cube which could be estimated to be half the primary projection, i.e. about 10 mm. Additionally, in this individual the longest undertail-coverts were plain white (not visible here). This bird’s old tertials indicate that it hatched in 2013.

8. First winter Arctic Redpoll

The third individual (9-12) shows the narrow flank streaks and the creamy throat (more obvious when seen head-on, as in photo 10), but its head seems to be more streaked. Compared with an average Mealy, the head streaking is still much less pronounced. In this bird the bill looks rather long and, although seen from the side only, it seems to have all-white undertail-coverts and an all-white wingbar. Some unstreaked white on the rump can also be seen under the raised wing. Photo 11 illustrates that, indeed, there is a large sugar cube. The slight pinkish hue is caused by the low sun and can be seen on the snow as well. And the final photograph showing this bird reveals that there is no shaft streak on the longest undertail-coverts.

9. Arctic Redpoll

10. Arctic Redpoll

11. Arctic Redpoll

12. Arctic Redpoll

We have three more individuals to complete the set for Arctic. First (13), a bird with a sugar cube of about 10 mm, white undertail-coverts (cannot be seen for sure on the photo, but this was confirmed in field), few narrow rear flank streaks and a less streaky head. Then two photos (14 & 15) of another individual with a creamy face, few flank streaks, this time a bit wider and—when seen from behind as in photo 15—this bird seems to be “frozen over”, a feature often mentioned for the jizz of Arctic. Other, because of their too low quality already deleted photos, confirmed that it had a rather large sugar cube and all-white undertail-coverts. The last Arctic for now (16 & 17) can be aged as first winter by its very pointed tail feathers. This is a good example to show how much white Arctic can show in their first winter. But unfortunately not all are like this. From behind (17) it almost looks like a white snowball with only a very narrow shaft streak on the longest undertail-coverts. Note also the very thin flank streaks.

13. Arctic Redpoll

14. Arctic Redpoll

15. Arctic Redpoll

16. Arctic Redpoll

17. Arctic Redpoll

Mealy can show a creamy ochre colouration of the throat and lower cheeks (extending down to the upper breast in most individuals of both species but usually not reaching as high up on the cheeks) as can be seen in photo 18, but this bird’s head is much streaked, its outer part of the wingbar is orangey-brownish and two dark rows run well down to the rear flanks. Further, this bird is not short-billed and has a distinct dark border to the rear of the ear-coverts. It can clearly be seen in photo 19 (same bird as in 18) that the rump is completely streaked, and the longest undertail-coverts (not shown well enough here) showed a broad shaft streak. Note that each undertail-coverts shows a shaft streak.

18. Mealy Redpoll

19. Mealy Redpoll

The following bird (featured in photos 20-22) also has the pale creamy throat and upper beast and in photo 20 its undertail-coverts are seemingly all-white. Photo 22 shows how misleading a single photo can be! Of course it has two rows of wide flank streaks plus a third, fainter one, a long bill, strongly patterned ear-coverts, a slightly darker outer wingbar and a streaked rump, completely lacking the sugar cube (21).

20. Mealy Redpoll

21. Mealy Redpoll

22. Mealy Redpoll

A first winter Mealy is shown in photos 23-25. This one looks rather dark and has the fused flank streaks, no sugar cube (24) and a nice triangular (though on the narrow side for Mealy) shaft streak on the longest undertail-coverts and also streaks on the shorter undertail-coverts (25).

23. First winter Mealy Redpoll

24. First winter Mealy Redpoll

25. First winter Mealy Redpoll

Since we are already looking at the undertail-coverts: Here are two more examples to document the variation seen in Mealy (26 & 27). Photo 26 shows a classic pattern: all undertail-coverts show a shaft streak, with the one on the longest being very broad. On the bird in photo 27 the undertail-coverts are dominated by the obvious shaft streak on the longest undertail-coverts whereas those on the other undertail-coverts are very faint or lacking.

26. Mealy Redpoll

27. Mealy Redpoll

Not all Mealy are warm brown as can be seen by the next bird (28 & 29). This one is “mealy” and greyish but lacks the sugar cube, has a lot of flank streaking, streaking on the shorter undertail-coverts is visible (but the longest undertail-coverts were not checked) and a dark rear of the ear-coverts. As it faces away in photo 29, its bill looks rather small. Be aware of this!

28. Mealy Redpoll

29. Mealy Redpoll

Our final example is one of the most easy to identify Mealy (30-32). Photo 30 not only shows the undertail-coverts at their best, but also the darkish ground colouration of this Mealy, which is obvious in the other two photos of this individual, too. Note, what looks like a sugar cube in photo 31 (between the tertials) is actually just a white streak on the bird’s rump. A closer look will reveal that this white streak is bordered by dark streak (emphasizing that these bird require an inspection as close as it is necessary for identifying a large white-headed gull!). The last photo shows that the bird has much streaking on its rear flanks and does not belong to the shorter-billed cohort.

30. Mealy Redpoll

31. Mealy Redpoll

32. Mealy Redpoll

Appendix: Two short notes on taxonomy and systematics

Redpolls were formerly placed in the genus Acanthis. In most publications they are nowadays within Carduelis, while more recently they have been returned to Acanthis (cf Zuccon et al. 2012).

Furthermore, the taxonomy of redpolls is unsettled. Molecular genetics have failed to find clear differences between different taxa of redpolls, including between Mealy and Arctic. Apparently there is a continuum, with strong gene flow between northern and southern populations, and between west and east (Marthinsen et al. 2008). BirdLife International treats all redpoll taxa as one species nowadays. However, this is not really influencing the facts about ID which have been told here.


Literature

Jännes, H. (1995). Die Bestimmung des Polarbirkenzeisigs Carduelis hornemanni [in German; Identification of Arctic Redpoll Carduelis hornemanni]. Limicola 9: 49–71.

Lewington, I, Alström, P. & Colston, P. (1991). A field guide to the rare birds of Britain and Europe. HarperCollins Publishers.

Marthinsen, G., Wennerberg, L. & Lifjeld, J.T. (2008). Low support for separate species within the redpoll complex (Carduelis flammea-hornemanni-cabaret) from analyses of mtDNA and microsatellite markers. Mol. Phylogen. Evol. 47(3): 1005–1017.

Svensson (1992). Identification Guide to European Passerines. 4th revised and enlarged edition. British Trust for Ornithology.

Zuccon, D., Prys-Jones, R., Rasmussen, P.C. & Ericson, P.G.P. (2012). The phylogenetic relationships and generic limits of finches (Fringillidae). Mol. Phylogen. Evol. 62: 581–596.


dig deeper: some further links

Identification of Redpolls, a compilation (PDF, 286 kb)

Lesser, Mealy, and Arctic Redpoll Identification

Intermediate Arctic Redpoll

Arctic Redpoll identification revisited (PDF, 1.5 MB)

Redpolls in the Sibley Guides

North American Redpolls