How many morphs do we know for Atlas Long-legged Buzzard? – Andrea Corso
In all the available field guides, but also on major work such as Cramp & Simmons (1980) there are no mention neither illustrations of any other plumage of Atlas Long-legged Buzzard (Buteo rufinus cirtensis) but the pale one which is the best known and the most widely photographed, corresponding to the pale plumage of nominate subspecies rufinus. Indeed, most of the European birders still know and could ID only this plumage, while some other recently started to realize that the variability is much higher, even higher than in nominate; indeed, back only in the 2006 there were some reports in Spain (one at Cazalla, Tarifa on 23rd September 2006; one at Cadìz, 14th September, 2006) of some “odd” Buteo sp., identified as vulpinus by all birders while considered cirtensis by myself (http://www.rarebirdspain.net/arbsi033.htm). Indeed, regularity since 1999 I started to study the matter, as I am very passionate about North African birds and zoology in general there. In the Rare Birds in Spain paper above mentioned, for the first time I reported about all the other plumages (including the at the time unknown in modern literature “grey-brown birds”) that I observed on Atlas Long-legged Buzzard, with several details on the identification of this taxon. Since then, I got tens of photos, mostly from Spanish and Portuguese birders, asking for an opinion on the identity of several buzzards there observed time by time. I answered in details with all the characters, as long as I could, but was clear even to myself first that the problem was far more complicated, and that simply, many birds should have left unidentified or deserved a more in depth study. Therefore, I visited museums to handle all the skins and, more importantly, I visited North Africa and the Middle East since 1999 annually, 3 to 5 times per year. I have been looking at pairs at nest (20 in Tunisia, 10 in Morocco, 2 in Egypt) year by year, and I was carefully checking all the observed birds. My results will be published on an extensive article in due course in Dutch Birding where the fruits of this long study will be printed on paper, alongside with many photos and plates but here I whish to report at least about the morphs of that fascinating, least known Western Palearctic raptor. I hope you will like this short summary.
For a matter of easier description, we could include into three main plumages or “morphs” the appearance of adult birds but with many intergradations and gradual changing which constitute a spectrum of colour gradient : 1) a pale plumage that vary from a very pale, almost sandy-white (which is most common on desert areas) to a more patterned and contrasted plumage, the one typically shown in field guides and references and 2) a rufous plumage, which is a rich rusty-warm colour quite uniform coinciding with the fox-red plumage of vulpinus, found all along the distribution range, but less illustrated and described, grading into a 3) darker plumage (here described separately for a matter of relevance) which may be the darkest end of the pigmentation variability, being grey-rusty brown, very much the same the grey-brown morph of vulpinus and often even extremely similar to many buteo (chiefly of the southern populations), more commonly distributed in the northernmost part of the range and that is the least known plumage of all. The existence of a third type, a dark morph, is also discussed though is not yet proven behind any doubt. Juvenile mostly show two main plumage with several intermediate birds: a most common pale plumage with more or less extensive dark patterning (like the streaking of underbody) and a much darker, browner, more patterned plumage which could be less broadly dark marked or with dark markings wider and more extensive. The presence of a pale U over the belly or the breast as on Buteo buteo ssp. vary a lot, and is more commonly found on darker birds, while, contrariwise to the rufous morph in the nominate taxon where it is very rarely shown, regularly rufous plumaged cirtensis may show this marking though often is indeed lacking.
1) PALE, BEST KNOWN PLUMAGE
Adult – In all the field guides today available, only the plumage closest to the most common one in nominate is described and illustrated, ie the pale morph which is always, also in the nominate, the easiest to identify and the most typical. Adult birds are rather easy to identify and to distinguish from buteo and also from vulpinus, despite the small size and the more compact looking enhance the similarities between the latter and cirtensis. The plumage is rather richly coloured, with a tendency to orange-buff, ochre or orange-reddish colour, as in nominate rufinus, with typically breast and neck to head paler than the remaining underparts, which are always darker, with in fact darker brownish-rusty trousers and flanks. In flight, the dark areas underneath stand out as two body side dark patch in an otherwise pale bird. Compared to nominate however, flanks and trousers have usually a more reddish or rusty-orangish hue, lacking the blackish hue of nominate, and often the lowest thigh feathers are paler and least marked. In many birds, the trousers (thighs) and flanks are only marginally darker and slightly rustier than the rest of the body, or even concolours with the body. However, contra for ex. Svensson et al (2009) and many other references, the thighs could be also as dark as in nominate, sometimes also in birds belonging to this “morph”. The belly and lower vent are usually paler than in nominate, and in this plumage usually least patterned. Therefore, the contrast between higher underparts and lower underparts, shown as a be-colour impression is more obvious and striking in the nominate race while it appear most of the time more “patchy” dark and pale in cirtensis. Indeed also, the head and neck stand out less dramatically than in nominate, the forehead and the crown being in most birds darkish, forming often a darker “hat”, and the neck is more streaked by pencil-like dark streaks. Also, more often than in nominate, there is a contrasting paler U over lower breast, similar to the one shown by buteo and vulpinus though usually less marked and less obvious. The carpal patch is almost black (though tinged rusty or brownish more often than in nominate) and is usually rather solid and extensive, however, note that more frequently than in nominate race the carpal patch could be reduced to a dark “comma” at wrist or a “double comma”. The tail is very bright and richly coloured, once fully and definitely in adult plumage, is cinnamon-orange or rusty-orange when fresh, fading once abraded (and sun-bleached) into a off white or creamy white. When typical, the tail, is to be considered immediately different from any vulpinus, even the most colourful fox-red-morph (Forsman, 1999; Clark, 1999; Shirihai & Forsman, 1991, Shirihai al. 1996; pers. obs.) being richer coloured, more orange and showing no dark barring. In palest birds the tail could be often creamy-buff even when fresh and not only when abraded and sun-bleached as in all rufous birds. Mostly younger adult usually show a various amount of dark barring (form 1 to 8 or 9 dark bars), which are often irregularly patterned and irregularly diffused among the different tail feathers and on inner and outer webs. FOR MORE IN DEPTH DISCUSSION ON TAIL BARRING SEE CORSO, IN PREP. Legs and cere yellow, sometimes bright yellow (mostly males) and in other birds tinged greenish (mostly in female when pair seen at nest). – White birds: some birds, mostly from the southern desert area of the breeding range, show an extensively very pale plumage that is so well defined that could even be differentiated in a paler type plumage or “morph”. They show an almost fully white-buffish underparts, sometimes, the thigh-feathers are slightly orange or cinnamon-creamy, other times there is only an hue of orangish tinge on flanks and thighs. Uderwing coverts are ocreous or buff, very pale and unmarked, with a very obvious and contrasting black carpal patch never observed like so in buteo and in vulpinus. The carpal patch in the palest birds is however sometimes missing and limited to a dark or darkish “comma” at wrist. Upperwing coverts are also often rather whitish, appearing the upperwing (chiefly if abraded) strongly two-coloured as on abraded juvenile Short-toed Eagle in 2nd calendar-year. Indeed, in the field, these birds are often very similar to a late 2CY Short-toed Eagle. Note: Of course, this plumage is the one which abrade and that chiefly sun-bleach sooner and more obviously, due to the fact that is mostly found in desert areas! The white impression is therefore even more striking for that reason.
Juvenile – Typical juvenile bird appear normally rather pale, with least marked underbody, chiefly an almost unmarked breast and higher belly with very narrow darker pencil streaks. The dark spotting/streaking its often more conspicuous to the side of the breast, while in most case the central area its least marked or clean. Lower vent and thigh feathers are usually more marked, more patterned and darker, as well are the flanks, those are in the higher part more frequently than in typical adults tinged blackish as in nominate or at least slaty-grey dark brown. The darker flanks and partially the thigh-feathers stand out strikingly in flight as sides dark patches over an otherwise pale bird. Normally the whole plumage its below a pale buffy – creamy white that soon bleach into off white, and a pale brownish above with a cold grey cast, mostly over wing and typically over the tail where there is extensive frosty icy off white or greyish-white, in wide pale areas. Conspicuous is a darker crown and forehead giving an “hat” impression and enhancing the pale supercilium, while the nape its pale, off white. These, combined to dark obvious moustachal mark and often, but less, a broad dark eye-stripe give to the bird a very Saker-like impression. Underparts marks usually shaft streaks, a barely barred pattern to some flank feathers, while adult shows extensively barred feathers. On underwing, greater and most median coverts unmarked white, lesser and marginal coverts show instead dark shaft marks. Carpal patch less striking than in adult being more peppered/patterned pale. Among typical juvenile as for adult there are some palest plumaged bird, that we may call the white-morph, that appear almost fully off white with barely some sparse darker drops (pale brownish or pale rufous-rusty) on lateral corner of the breast and vent. In this birds, the flanks still are darker and more marked, but much less than in typical plumages, and the thigh-feathers, noticeably the lowest trousers, are often also fully off unmarked white. When faded and sun bleached, from upper view these birds looks like a small abraded juvenile Short-toed Eagle, with contrastingly paler upperwing coverts and head. Structure typical of juvenile buzzards compared to adults, with narrower wings, more S shaped on lower profile, shorter and broader “fingers”, longer tail. Iris variably pale colored, from yellow to yellowish grey or dark sullied grey (sexually or individually related?), sometimes remaining greyish up to 2 years (pers. obs.). Bare parts bright yellow, just barely tinged bluish when into the nest and mostly the female (pers.obs. and contra several references).
2) RUFOUS PLUMAGE
Adult – Never illustrated in any modern field guide, is a second morph, the rusty-rufous or simply rufous. Birds with this plumage are more common to the north of the breeding range, but is sometimes found also to the south. This plumage show a rather extensively warm rusty brown or reddish plumage, with duller or rustier flanks, thigh-feathers and middle belly, darker and more contrasting in most birds than undertail coverts, lower belly and breast which are paler and cleaner. Sometimes the thigh-feathers and the flanks are tinged dark sooty grey or blackish-brown. Usually, the undertail coverts are rather paler, being orange or pale creamy almost off white like the lower belly and the breast. These area may be uniform or barred/blotched with marks being deeper rusty or brownish. The breast its uniform in the real rufous or fox-red plumage, or with shaft streaks more reddish or darker rusty, but could be frequently streaked with blackish-brown or dark grey. In several birds it is noticeable a paler U over the breast, like the one in buteo and vulpinus, more frequently that on the nominate subspecies, but often there is no hint of such a pale U pattern. The head its rather uniform with the lower parts but show a darker crown forming a dark “hat”, dark moustache, malar and gular stripes. Underwing coverts are usually rather uniform and reddish or rusty, with a variably extensive and marked black or blackish carpal patch, however always wider and more contrasting than in typical buteo and typical vulpinus (but exception exist). Upperparts browner and darker, with extensive rusty or orange-reddish broad fringes when in fresh plumage. Tail as for pale plumages but usually more often and more extensively barred even when fully adult, or more rusty. In some birds the tail is dark sooty grey, tinged rusty and brownish, mostly at the central part along the shaft, always with a cold frosty tone lacking in buteo and vulpinus.
Juvenile – As the juvenile of the pale plumage but more extensively dark marked, duller, more patterned, with darker underwing coverts, darker tail with wider barring, more patterned undertail coverts and thigh-feathers and flanks, darker head. Some show wider dark shaft streaking over breast, neck and belly approaching very much Common Buzzard of the nominate taxon, mostly the birds from the southern populations, being almost identical for ex. to juvenile buteo from Southern Spain, Southern Italy, Sicily, and hardly distinguished from them (see under Identification – note especially tarsus length and strength, bill size, gape line, hovering attitude, calls).
3) RUSTY-BROWN AND GREY-BROWN BIRDS
Adult – This is the least known plumage, never shown in literature. This plumage is found mostly on the northern part of the distribution range of cirtensis and may constitute the darkest end of the rufous-brown pigmentation of the colour range spectrum in the species. Some birds show a brownish plumage rather uniform, quite similar, sometimes almost identical to same morph in buteo and vulpinus, usually the brown is warm and with a rusty hue, but few birds have a really grey-brown plumage. In some darkest examples, this plumage could be considered the equivalent of a dark morph, though not the chocolate-blackish morph found in nominate rufinus and in vulpinus. In those birds, the dark extensive and marked carpal patch, the structure (as the long and robust tarsus and heavy bill), and the full set of characters are indispensable for a positive identification. NOTE: However, should be kept in mind and accepted that it is better to leave unidentified many – or most- of the birds in these plumages if the tarsus length is not seen perfectly and the call not heard alongside other characters (reported in Corso, in prep.). For example, grey-brown juvenile is in most case impossible to tell apart unless not seen perched very close or in the hands obtaining biometrical measurements. NOTE 2: genetic study should be done to verify if the birds in such plumages have or not pure genes of cirtensis. Indeed, they may be hybrids or may be the result of a genetic introgression with Buteo buteo ssp. from Europe (as shown for other sister taxa like Pine Bunting and Yellowhammer for example). The recent extensively documented and well diffused cases of mixed pairs producing hybrid offspring of buteo x cirtensis in several southern European countries such as Sicily (Pantelleria island, Sicilian Channel – Corso, 2009), Spain (Elrroiaga, 2010) and Portugal (L.Palma, pers. com.) demonstrate that this is possible, and al least in European grounds already happen, in some areas also regularly and quite extensively (since when ? only recently?). In fact, should be stressed that many birds observed also in Northern Africa are impossible to be identified to a specific level at least on phenotype appearance only. It should be taken in mind, before DNA results are widely done and available to finally clarify this conundrum, that in museums there are skins of grey-brown plumaged Atlas Long-legged Buzzard, collect in the breeding grounds and during breeding season in the ‘800 and which I re-confirmed as showing the characters of cirtensis by their morphometric measurements (such tarsus length, bill height, wing-chord, tail length); this would means that if these are hybrids with Buteo buteo ssp. or the fruit of a genetic introgression, then the phenomenon occur since some hundreds years. Genetically, this is surely possible, as the genetic differences and distances are very low, with all the European Buteo sp. so close each other that some authors proposed to lump them into a superspecies (Riesing, et al. 2003; Kruchenhauser, et al. 2004). These authors report that “ In the genetic analysis, almost no sequence variability was found among taxa comprising the buteo–vulpinus complex as well as Buteo rufinus and Buteo oreophilus , suggesting gene flow and/or incomplete lineage sorting.”. This could imply that Atlas Long-legged Buzzard is either a “younger” taxon than the nominate ssp., or that is among the Western Palearctic taxa of Buteo sp. the one which show more regularly and visibly characters derived from the ancestor parents.
Juvenile – even darker than the rufous juvenile, with very extensive dark patterning like wide shaft streaks and spots or extensive blotching with some feathers area wholly earth- brown. Most of the juvenile of this browner plumage are identical or nearly so to many Buteo buteo ssp. and only different in few characters hardly seen in the field, such for ex. the tarsus length (but see Corso, in prep.).
– Dark morph
All authors report that cirtensis lack the dark morph (Shirihai et al., 1996, Svensonn et al. 2010, Cramp, 1980, Ferguson-Lees & Christie, 2001, Clark, 1999). Corso (2002) discussed the possible existence of an extremely rare dark morph, based on a video on Tunisian raptors by J-M. & M. Terrasse from 1987 where an Atlas Long-legged Buzzard going to a nest, filmed in Northern Tunisia, seems to be fully dark chocolate or warm brownish dark. Being a dark morph in cirtensis considered lacking by all the previous authors, caution is required. However, several Buteo sp. observed on the breeding range of cirtensis by several observes were in a dark chocolate brown plumage (see more details in Corso, in prep.). I do not yet consider sure the existence of a dark morph in cirtensis, though extremely rare, before obtaining good photos or a skin. However, in light of the reported observations, I think it is better to warn any visiting birders of the breeding range of cirtensis to be aware and to search for this plumage.
(other sources not reported – see Corso, in prep.)
Corso, A. 2006. Some notes on the identification of North-West African Long-legged Buzzard Buteo rufinus cirtensis. http://www.rarebirdspain.net/arbsi033.htm
Corso, A. in prep. Identification of Atlas Long-legged Buzzard. Dutch Birding
Kruckenhauser, L., Haring, E., Pinsker, W., Riesing, M. J., Winkler, H., Wink, M. & Gamauf, A. (2004). Genetic vs. morphological differentiation of Old World buzzards (genus Buteo, Accipitridae). — Zoologica Scripta, 33, 197–211.
Riesing, M. J., Kruckenhauser, L., Gamauf, A. & Haring, E. (2003).Molecular phylogeny of the genus Buteo based on mitochondrial marker sequences. Molecular Phylogeny and Evolution, 27, 328–342.