Commentary on Philippe Dubois' Paper on Atlantic Yellow-legged Gulls

Commentary on Philippe Dubois' Paper on Atlantic Yellow-legged Gulls

Sources:

Dubois, P J, (2001), Atlantic Islands Yellow-legged Gulls, an Identification Gallery, Birding World 14(7) 293-304.

Yésou, P, (2002), Trends in Systematics, Systematics of Larus argentatus-cachinnans-fuscus Complex Revisited, Dutch Birding 24(5) 271-298.

Field work:

Canary Islands: September 1991 (author)

Azores: mid-August 2000 (author)

Canary Islands: late July 1997 (Jiguet)

Specimens: from Azores, Atlantic Morocco and Madeira.

Terminology:

While in both papers above the term atlantis is erroneously reserved for those from the Azores (see below), here the term is used as by Dwight (1925) extending to the Azores, Canaries, Madeira and Atlantic Morocco with extension to Atlantic Iberia by the studies of Rossiter (2002). The term michahellis is used here for the Mediterranean Yellow-legged Gull.

Claims by Dubois	Comments NR
p.293 General
Scanty treatment in the literature of Atlantic Yellow-legged Gull Larus michahellis atlantis	For birds of known origin atlantis is as well covered as michahellis in the printed and electronic literature. See for instance Dwight's Original Texts on atlantis, Home Page Yellow-legged Gulls and Norman van Swelm's ID paper . For wingtip patterns of michahellis in their breeding areas we are reliant on Isenmann (1973).
Dwight first described the form atlantis from the Azores and that the Azores form is the true atlantis.	Not true -- see Dwight's Original Texts on atlantis with commentary
Third-years from the Azores show dense streaking on the head, look completely grey-hooded at a distance -- a feature unique to Western Palearctic Gulls.	This is certainly a striking feature. However, some third-winters in the western Canaries can also show quite marked hoods.
Juveniles and first-winters from the Azores are quite variable but are still often identifiable.	Very doubtful - juveniles from Madeira and the western/central Canaries can be as dark
p.294 Structure and Jizz
atlantis are generally more compact, shorter-legged and shorter-winged than michahellis. Many atlantis also have a somewhat heavier and less 'hatchet-tipped' bill than michahellis. Sexual and individual variation, however, mean that structure is of little use for identifying a lone bird.	The biometric differences between atlantis and michahellis are well established -- see Available Statistics: Tables 1-2 and Norman van Swelm's ID paper . Some of the differences are very significant such as leg difference and could be used to support strongly the identification of a lone bird.
Juvenile
Juveniles from the Azores in mid-August are very dark (some recalling juvenile smithsonianus)	Agreed. Juvenile atlantis could be confused with smithsonianus
Dark chocolate upper mantle, those from Canaries often paler and more chequered	In July 95% of juvenile atlantis in Tenerife are a dark grey-brown and only 30% are chequered Statistics for First-years: Tables 6-8 . Therefore this claim is not accepted. Also not all the Azores examples shown appear to be uniform in texture.
Head colour is variable but usually like in Madeira birds show a darker head than birds from the Canaries where streaking is mainly around the eyes.	95% of Tenerife birds in late July show a very dusky head. See also plate 12 of Dubois' paper for a counter-example. Not accepted.
Fairly uniform scapulars	As in 70% of Tenerife birds in late July
Tertials are similar to michahellis with many having fine pale fringes or pale indentations or notches.	This is very interesting. Of five shown in Dubois' paper, three look to me like graellsii (narrow fringes) and two show notched fringes. 88% of southern atlantis show graellsii-type pattern Statistics for First-years: Tables 6-8 so if confirmed on a larger sample, Dubois' finding is significant. However, genetically it would suggest that Azorean atlantis is close to michahellis as suggested by Liebers et al (2001). Some northern atlantis also show more white on the tertials (Stats ibid).
In flight obvious dark secondary bar and dark greater coverts bar, many lack a pale window on inner primaries. Canary birds do usually show a faint pale window.	50-60% of juveniles in Tenerife show two bars on the inner-wing in July and August. 75-80% of juveniles in Tenerife in July and August have an indistinct pale primary window (often difficult to see) and 15-20% no window. Possibly some difference at the population level but we need statistics from the Azores.
Dark underwing coverts with slight contrast from the primaries.	Rather similar in the Canaries with 45% of juveniles in July and August showing some contrast and 20% no contrast
Broad dark tail band unlike typical michahellis	As in Canaries
Dark markings on front of tarsi and on the feet. Madeira birds are similar. In michahellis such markings are shown less commonly	An interesting observation but, if shown by Madeiran atlantis, is obviously not specific to the Azores. Slides at IGM6 showed this feature on juveniles from Fuerteventura in the first half of November (Andreas Buchheim).
p.298 First-summer
It is not always easy to distinguish between juveniles and first-summers in mid-August. The Canarian birds become much paler on head and underparts.	The difficulty of distinguishing juveniles and first-summers also applies in the western and central Canaries where primary moult is one of the criteria used. Birds in Fuerteventura have a greater tendency to become paler.
Uniform underwing	As in the Canaries
p.299 Immatures
Plates 21 and 22	Not accepted as typical Canary birds. A few % of first-years in flocks are large and strong with long legs and pale heads and bodies. But these untypical birds are either extreme atlantis or visiting michahellis. Some much darker birds could have been shown here with the typical structure of atlantis.
p.300 Second-summers/third-winters; plates 22-29
Head streaking	See above
Moult in atlantis starts earlier than in michahellis and is perhaps more prolonged	Not sure that this can be inferred from studies only undertaken in late summer and autumn. However, Canary birds do seem to be slightly ahead of michahellis but the difference is small.
Iris is very pale whitish-yellow in Azores and Canaries while in michahellis it is a relatively dark yellow	Agreed that it is a very pale yellow in atlantis but michahellis from SW France and eastern Andalucia also seem to have very pale iris as do a number of adults and older immatures shown in various web pages. The bird in plate 29, alleged to be michahellis, is rather strange. Its head is quite streaked and its legs are rather short. Its origin is surely unknown.
p.302 Adults and near-adults
Iris colour	See above
Two types noted in late summer: white heads and obviously streaked heads, the latter possibly fourth-winters.	An important observation. Possibly the adults are closer to other atlantis than generally realised.
p.304 Discussion
Plate 30 (skin comparisons) indicates a clinal change in mantle colour from michahellis (palest) to Essaouira, Atlantic Morocco to Madeira to Azores (darkest)	The effect may be exaggerated as the Azores bird is in fresh September plumage and the michahellis and Morocco bird are in more worn April plumage (no month for Madeira bird). However, all three atlantis are significantly darker than the michahellis as expected.
No mtDNA difference between michahellis and atlantis by Helbig.	Differences now found -- see Liebers et al (2001) Review of recent genetic analyses and comparison with morphological work
Azores atlantis is distinct from michahellis	Agreed
The Canarian form is close to the Moroccan one	Agreed -- they are both atlantis
The Canarian form is closer to michahellis than to Azorean atlantis	Not if you consider size, structure, wing-tip pattern in adults, mantle shade and juvenile plumage characteristics.

Discussion:

The paper by Philippe Dubois does provide some excellent photographs of Azorean atlantis but there is a shortage of statistics and analyses to give a real impression of what the Azorean gulls look like as a population.

Interesting aspects are the variation in tertial pattern and the heavy head streaking in late summer on older immatures. However, these may suggest some affinity to Iberian atlantis as well as to the southern form (Southern atlantis).

Considering how little we know about the Azorean population, it is surprising how much is said about it. Perhaps its mystery status excites some of the interest. It would be nice for instance to know what its calls are like.
The islands from which the Canarian examples are taken are not given. This is an omission as there are some clinal differences in Canarian atlantis from east to west.
The claimed differences from the Canarian atlantis are not supported by the detailed statistics obtained for this form and cited above. Juvenile Azorean atlantis may have slightly more white on the tertials but this might suggest that they also have some affinity to northern atlantis or even michahellis. Their renowned dark heads and underbody are found in the great majority of Canarian atlantis in July and August.
One factor which is ignored by many casual visitors to Macronesia and the nearby Atlantic coasts is the variation in climate across the area, even over quite small distances. Thus Fuerteventura and southern Morocco have virtually desert-like climates with low rainfall, long periods of strong sunshine and strong winds, sometimes sand-laden. As the Canaries are traversed westwards the humidity, cloud cover and rainfall increase so that El Hierro and La Palma have a much damper climate than Fuerteventura. Madeira is more humid again and the Azores are the most humid of all with substantial rainfall, cloud cover and wind. The main winds in the Canaries are the North East Trades which give much more cloud and drizzle on north-facing coasts than on south-facing ones. Hence early civilisation here was mainly on the north side and the modern tourist trade is on the south side.
The climate has a number of effects:

Photographs of gulls can give a misleading impression as to head streaking and mantle shade.
Most of Dubois' photographs in the Azores are clearly taken in mist and poor visibility (plates 1-4, 9, 11, 15, 18-19 in particular). Compare these with plates 5 and 27 also from the Azores in sunshine. The birds look completely different and much more like the Canary birds, nearly all of which are taken in the very bright sunshine of that area.
Indeed to prove this point further the only plate (12) taken in the Canaries in dull light shows a juvenile looking quite close to the Azores ones.
Also some shots of Azorean atlantis by Cursorius on their web page recently show quite variable head markings, not that different from those in the Canaries.
Fading of plumage will be faster in the climate of Fuerteventura and south Morocco than in the western and central Canaries, Madeira and the Azores.
Heavy head and body streaking will be retained longer in northern and western atlantis than in south eastern atlantis.
However, this rapid wear is not usually to the extent indicated in plates 20-21 which presumably claim to show typical Canarian birds. The birds shown are more likely to be visiting michahellis or extreme atlantis (few % of population). The leg length is too long for the vast majority of atlantis.

The differences between the Azores and Canary atlantis have therefore been greatly exaggerated in the plates and the paper by ignoring the effects of weather and climate.

Conclusion:

The conclusions reached by Yésou (2002), after assuming the claims above, is untenable.
In particular the three statements by Yésou (p.288) below are considered to be without foundation:

1) atlantis ... has been described from the Azores (Dwight, 1922). Some authors ... extended this name to the birds breeding in the Canary ... and Madeiran Islands ...

In reality Dwight (1925) defined atlantis as occupying the coasts and islands of north west Africa and used specimens from the Canaries in his 1922 paper.

2) More recently Dubois (2001) concluded from field and museum studies that Azorean birds differ from those breeding in the Canary and Madeira Islands in a number of aspects.

There may be some minor differences but there is as yet no phenotypic evidence for any separate taxonomic treatment.

3) It is wise to restrict the use of the name atlantis to the birds breeding on the Azores as Dwight initially did ...

We should certainly consider atlantis to occupy the range given by Dwight in his 1925 paper. Modifications using results from recent studies lead us to also include most of Atlantic Iberia within the atlantis range.

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