Adult Atlantic Yellow-legged Gulls atlantis may be identified by a combination of factors from other gull species. The list below is provisional. The weighting to be attached to particular factors and the number required for a positive identification is under review. Differentiating features between populations are that the Atlantic gulls have relative to:

1. generally heavier appearance around the head and chest;
2. heavier bills with stubbier tips;
3. less graceful and distinctly heavier and more ponderous appearance in flight;
4. broader wings;
5. less attenuated appearance at rest with tail tip from midway between P6 and P7 to P7 as opposed to P6);
6. slightly less dark mantle and bluer-grey sheen rather than neutral grey;
7. shriller long calls;
8. long calls given at 60° rather than 90° ;
9. blunt wingtip giving bunched primary tips on the folded wing with in lengths P10=P9, P9-P8 < P8-P7, P8-P7=P7-P6 (as opposed to P10>P9, P9-P8 = P8-P7, P8-P7=P7-P6);
10. more white in wingtip with increased chance of white tip on P10 (45% of birds) and of mirror on P9 (23%).
11. less black on wingtip with reduced chance of a broad black band on P5 (46%) and much less chance of a black mark on P4 (11%);
12. sharper division between black and grey areas on upper wing;
13. not so obvious dark trailing edge on the underside of the secondaries.

1. darker mantle, being darker than Common Gull L. canus;
2. yellow-ochre legs;
3. red orbital eye ring;
4. deeper long calls (approaching graellsii) and mew calls like graellsii;
5. long calls given at 60° rather than 45° ;
6. larger and redder gonydeal spot on bill;
7. less white on P9 with only 22% carrying a mirror;
8. more black on wingtip with a solid triangular black area from tip on outer web of P6 to visible base of P10 to tip of P10 lacking visible pale inner tongues.

1. smaller size by 5-10%;
2. shorter and slightly narrower bills;
3. less attenuated appearance at rest with tail tip from midway between P6 and P7 to P7 as opposed to P6;
4. shorter legs, typically 70% of height of body above legs compared to about 100%;
5. rounded heads, lacking angular appearance;
6. blunt wingtip giving bunched primary tips on the folded wing with in lengths P10=P9, P9-P8 < P8-P7, P8-P7=P7-P6 (as opposed to P10>P9, P9-P8 = P8-P7, P8-P7=P7-P6);
7. smaller white primary tips on the folded wing;
8. slightly darker mantle shade with a marked blue-grey sheen;
9. shriller long calls lacking a guttural component, less deep mew calls,
10. long calls given at 60° rather than 90° ;
11. ochre tint to the yellow legs;
12. less white in wingtip with only 22% carrying a mirror on P9.

1. smaller size;
2. much less attenuated appearance at rest;
3. shorter legs, typically 70% of height of body above legs compared to about 100%;
4. shorter bill with stubbier tip and obvious gonydeal angle;
5. significantly darker mantle shade with a blue-grey sheen;
6. long calls sounding more like graellsii;
7. long calls given at 60° rather than 90° ;
8. ochre tint to the yellow legs with no pink tinge;
9. less white in wingtip with only 23% carrying a mirror on P9, only 45% carrying a tip on P10 and no pale tongues visible on the spread wing.

Note: the above applies strictly to Southern atlantis. See Iberian atlantis notes for some of the subtle differences between the forms of atlantis.

Blue font represents additions since paper published in October 2001

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