Atlantic Yellow-legged Gull (atlantis)

(last update: October 12, 2011)

Atlantic YLG 1cy October

Below you will find a description of AZOREAN YELLOW-LEGGED GULL (Larus michahellis atlantis), as published in Birding World Vol 14 No 7.

"I" in the text below refers to the original author Philippe Dubois, who visited the Azores in August 2000. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom. You can click the image (left) to get the PDF (3,18MB).

Atlantic Islands Yellow-legged Gulls: an identification gallery

Philippe Dubois (France)
IN: BIRDING WORLD, Vol 14 No 7

Of all the large gulls in the Western Palearctic, the Atlantic Islands Yellow-legged Gull Larus michahellis atlantis is one of the least-known. It has been scantily treated in the literature, although some information has been provided by Cramp & Simmons (1982), Grant (1986) and Garner (1997a).
The form atlantis was first described from the Azores (Dwight 1922), although birds supposed to be very similar also breed on the Canary Islands and Madeira. However, these latter birds, and birds breeding on the Atlantic coast of Morocco, may actually be intermediate between true atlantis and Mediterranean Yellow-legged Gull L. m. michahellis (Beaubrun 1988), or closer to the latter. Birds from Portugal and north-western Spain may also be allied to atlantis, but are actually closer in appearance to Herring Gull L. argentatus argenteus (Dubois 1986) and possibly represent another distinct form.
Although present all year on the Azores, atlantis is a pelagic feeder and does wander, so may be prone to vagrancy (Moore 1996), even to North America (Wilds & Czaplak 1994 and M. Gosselin in litt.) and Europe (see the bird photographed in Ireland in September 1994, Plate 138 in Garner 1997b).

True Azorean atlantis (hereafter referred to simply as atlantis) is quite distinct in some plumages. For example, third-years during their post-breeding moult show dense streaking on the head and look completely grey-hooded at a distance - a feature unique amongst the Western Palearctic large gulls. On the other hand, whilst still often identifiable, juveniles and first-winters are quite variable and can show a mix of characters which are very similar to nominate Yellow-legged, Lesser Black-backed L. fuscus graellsii/intermedius, and even some forms of Herring Gull.
This paper does not pretend to be an exhaustive treatment of the identification of atlantis and the other large gulls from the Macaronesian Islands. Its main aim is to present a photographic gallery of their appearance. The information presented here is based mainly on personal observations made on the Canary Islands in September 1991 and on the Azores in August 2000, with further information provided by other observers, particularly from Madeira (S. Nicolle pers. com. and Regan 1999), together with specimens from the Azores, Atlantic Morocco and Selvagem Grande (Madeira) examined at the Muséum National d’Histoire Naturelle (Paris).

Structure and jizz

The form atlantis and its close relatives from the Macaronesian Islands seem to be generally smaller, more compact, shorter-legged and shorter-winged than Mediterranean michahellis. Many birds also have a somewhat heavier and less ’hatched-tipped’ bill than nominate michahellis. There is considerable sexual and individual variation, however, so structure is of little use for identifying a lone bird such as a vagrant.

Atlantic YLG (atlantis), August 23 2010, São Miguel, Azores Islands. Picture: Richard Lowe. This adult is moulting into winter plumage, with some streaking on the head. Note that atlantis can appear rather short-legged.

Juveniles
Most of the first-years seen in early-August in Azores were still in full juvenile plumage and showed no sign of any post-juvenile moult. The most striking character of juveniles is the darkness of their plumage, on both the upperparts and the underparts; they are darker than most juvenile graellsii/intermedius and michahellis. Dark birds may recall some juvenile smithsonianus.
In the Azores, many juveniles have uniform dark chocolate upper mantle feathers creating a very dark area on the upperparts. Those from the Canary Islands at least are often paler, with this area more speckled with white, creating a more chequered effect reminiscent of juvenile Lesser Black-backed Gull. The head colour is variable: Canarian juveniles have whiter heads with black streaking mainly around the eyes, recalling graellsii/intermedius, whereas Azorean and Madeiran birds often show a darker head (either uniform brownish-grey or finely streaked).
The scapulars are like those of juvenile graellsii/intermedius and similarly variable, although some Azorean birds have more uniformly dark brown upper scapulars with narrow white tips, recalling darker smithsonianus juveniles. At rest, the coverts pattern recalls the chequered appearance of either nominate michahellis or graellsii/intermedius, but without the frequent cinnamon tinge of the former. The tertials are similar to those of many nominate michahellis, with the tips having either fine pale fringes or pale indentations or notches.

Atlantic YLG (atlantis) 1cy, August 27 2010, São Miguel, Azores Islands. Picture: Richard Lowe.	Am. Herring Gull (smithsonianus) 1cy, August 25 2010, St. John's, Newfoundland, Canada. Picture: Dave Brown.
Lesser Black-backed Gull (graellsii) 1cy, August 27 2008, IJmuiden, the Netherlands. Picture: Mars Muusse.	Yellow-legged Gull (michahellis) 1cy, August 27 2012, Katwijk, the Netherlands. Picture: Mars Muusse.

In flight, Azorean juveniles show an obvious dark secondary bar. Many also lack a pale ’window’ on the inner primaries, unlike most juvenile nominate michahellis, but juveniles from the Canary Islands usually do show a faint pale window. The outer and median greater coverts (and some of the inner ones) are plain, creating a dark greater covert bar. This bar is generally more obvious on Azorean birds since these normally have more inner greater coverts showing little or no pale barring.
The underwing coverts are dark, smoky brown (as in graellsii/intermedius and smithsonianus) and contrast slightly with the relatively pale brown primaries; nominate michahellis often shows a more gingery tone. The pattern of the tail and rump and uppertail-coverts is variable, but close to that of graellsii/intermedius: unlike typical michahellis, most juvenile atlantis show a broad dark tail-band, with white restricted to the outer rectrices, sometimes just as faint whitish identations on the outer webs of the outermost tail feathers (strongly recalling juvenile graellsii/intermedius and smithsonianus). On Madeiran and Canary Islands birds, the rump and uppertail-coverts are similar to those of graellsii/intermedius.

Atlantic YLG (atlantis) 1cy, August 24 2010, São Miguel, Azores Islands. Picture: Richard Lowe.	Am. Herring Gull (smithsonianus) 1cy, August 25 2010, St. John's, Newfoundland, Canada. Picture: Dave Brown.
Lesser Black-backed Gull (graellsii) 1cy, August 22 2008, IJmuiden, the Netherlands. Picture: Mars Muusse.	Yellow-legged Gull (michahellis) 1cy, August 11 2006, Amsterdam, the Netherlands. Picture: Mars Muusse.

All the juveniles I checked on the Azores and on the Canary Islands showed extensive dark markings on the front of the tarsi and on the feet. ]uveniles and first-winters in Madeira apparently show a similar pattern (S. Nicolle, pers. com.). Nominate michahellis juveniles may show such dark markings less commonly, and they seem to be more quickly lost in other species such as Herring Gull and Lesser Black-backed Gull. Interestingly, this feature occurs on Kelp Gull L. dominicanus too (Higgins & Davies 1996). The bill is black.

CONTINUE PART II

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BELOW: example birds for 1cy atlantis in October
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