Adult Dark Atlantic Yellow-legged Gulls 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.

Blue font represents additions since paper published in October 2001

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