Direct Comparison of Atlantic and Mediterranean Yellow-legged Gulls (atlantis-michahellis)

Identification Criteria for Adult Dark Atlantic Yellow-legged Gulls

Conil, Andalucia, south-west Spain, 12th August 2001

Six Yellow-legged Gulls, all michahellis except the one standing in the front of the group of four. Note the brighter bare parts on this bird and the shorter and less heavy bill as well as the other features noted below as differences

Conil, Andalucia, south-west Spain, 12th August 2001

Same group, different spacing, the atlantis is still in the front of the picture

Conil, Andalucia, south-west Spain, 12th August 2001

The atlantis is on the extreme right standing in front of a michahellis. This picture also shows two adult Audouin's Gulls and a michahellis juvenile in flight

Conil, Andalucia, south-west Spain, 16th August 2001

Of the three gulls facing left in the foreground, the ones sitting and on the right of the standing pair show characteristics of michahellis and the one on the left of the standing pair shows characteristics of atlantis. Notes taken at the time--

Atlantic form showed:

• Yellow-ochre legs (more ochre than pale yellow)
• Legs shorter (2/3 body, not 1/1 body, similar in length to LBBG)
• Darker mantle
• Blue-grey tinge to mantle (not wane grey)
• More mottled on front of head (not fine speckles)
• More compact appearance
• Rounded head (not boxy)
• Size much smaller (slightly bigger than LBBG)
• Tamer (kept in group while Med YLG left)

(No calls, an obvious further difference, were heard from the Atlantic form but the michahellis gave typical deep mew calls and deep guttural long calls)

The photographs below are larger than the usual ones on this site, up to c400k. Use of Automatic Image Resizing (in IE) will enable them to be viewed either in small or large format but transmission times will still be relatively long.

The larger size is used to enable the members of the flocks and groups to be studied in more detail. Identifying unusual gulls in flocks is of course the key to interesting gull identification. It is clearly possible to debate some of the assignments. It is more accurate to describe each assignment as 'showing the characteristics of ...'. The smaller birds seem more typical of intersection Atlantic-Med. populations rather than a purer atlantis as in the August 2001 example. There is considerable overlap in the birds involved between the photographs. Putative totals are given below together with moult comparisons.

Conil 4 June 2002 Photograph A -- flock in flight

Two Atlantic-Med. intersection 2s are on top and bottom of middle of picture. Note slimmer wings than michahellis, less bulky body, smaller head and bright yellow bill. Also on lower one there is an obvious dark blue-grey mantle.

Conil 4 June 2002   Photograph F - flock in flight

Audouin's Gull 1s is on top left. It shows a broadening secondary bar towards the primaries, all dark outer primaries and extensive dark on edge and terminus of tail, dark bill.

Three Atlantic-Med. intersection 2s are in the centre together. They all show bright blue-grey backs and scapulars, smaller heads and chests. One more of this form is on the bottom left of the picture following the darker bird.

One Atlantic-Med. intersection 1s is in flight against the white wall. This shows a dusky small head, is more lightweight generally and shows less contrast between back and wing. Some sparse mottling is shown on breast and belly. 

Conil 4 June 2002 Photograph B - flock on beach

One Atlantic-Med. intersection 2s is sixth from left on ground under flying michahellis 2s. The legs are short (c70% of body above). The head is slightly boxy, the legs rather thin, the bill is thinnish and yellow with a red gonydeal spot. Legs are pale ochre and there is an obvious secondary bar.

One LBB intermedius adult is on extreme left, the mantle is very dark, the head narrow and small, the legs short and both bill and legs have an orange tinge. It is clearly shorter-legged than the michahellis.

One Audouin's Gull 1s is towards the right (8th from right), looking very small against the michahellis and with relatively long dark fleshy legs.

The michahellis have long legs (almost height of body above), boxy heads, heavy stubby bills, thick necks.

Conil 4 June 2002 Photograph C -- flock on beach

Two Atlantic-Med. intersection 2s, one in flight at rear centre, the other 8th from the right. The one in flight shows a bright blue-grey back and scapulars, a broad tail band still, elegant narrow wings, small head, and a yellow bill to 3/4 from base. Another standing is quite lightweight with fine bill and thinnish short legs.

A number of large michahellis are available for comparison.

Conil 4 June 2002 Photograph D -- group standing on beach

Two Atlantic-Med. intersection 2s are walking away on extreme left and right; trailing moulting feathers, bright blue grey back and scapulars, very pale on the coverts with feather loss, bright yellow-ochre legs in one, other quite pale pinky-yellow. Both short legs at around 60-65% of body above .

One michahellis nearby (third from right) is 80%, other two are at wrong angle for measurement but long thigh bone obvious on one.

Two other Atlantic-Med. intersection 2s are facing in middle (3rd and 4th from left). These also have short upper legs (above knee). Heads of all are slightly boxy suggesting that they are probably from intersection zone.

Conil 4 June 2002 Photograph E -- group mostly sitting on beach

Four Atlantic-Med. intersection 2s are, from left, 2nd, 3rd, 4th and 5th (latter at back). These show obvious blue-grey back and scapulars, bright ochre legs and relatively slight structure. Legs are 70% of body on left bird and 50%+ (standing in soft sand) on right bird.

The michahellis show massive long heads with heavy long bills and thick necks.

Note total for Atlantic-Med. intersection is 5 compared to 33 for michahellis.

Note later moult of Atlantic-Med. intersection 2s compared to michahellis 2s.

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(c) Copyright Nick Rossiter 2002.

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