• Presence of mirror on P9
• Solidity of black triangle on outer primaries from P6-P10 (no indent)
• Absence of solid band on P5 (including slight break on shaft)
• Presence of black mark on P4

Table 1 below shows the features that were found to be significantly different between the various populations:

Table 2 below compares the populations of southern atlantis on the two sides of the Canaries: West (Tenerife, Gomera, La Palma, El Hierro) and East (Lanzarote, Graciosa, Fuerteventura, Gran Canaria):

Southern atlantis - W Canaries vs E Canaries:

• Southern atlantis, Iberian atlantis, cantabricans, argenteus, SW Spain michahellis, atlantis/michahellis intersection: this study (Nick Rossiter)
• Azorean atlantis: Teyssèdre (1983).
• Camargue michahellis: Isenmann (1973).

• P4, P5 and P6-P10 for the Azores
• P6-P10 for the Camargue

1. Southern atlantis is strongly differentiated from Camargue michahellis on all three parameters available (P9, P5, P4). Camargue michahellis has a greater tendency to white on P9 (100.0% vs. 22.5%), a black band on P5 (0.0% absence vs. 24.7% absence) and black on P4 (55.7% vs. 9.0%) .
2. Iberian atlantis is strongly differentiated from Camargue michahellis on two of the three parameters available (P9, P4). Camargue michahellis has a greater tendency to white on P9 (100.0% vs. 40.3%) and black on P4 (55.7% vs. 14.3%).
3. Southern atlantis is strongly differentiated from Iberian atlantis on two of the four parameters available (P9, P6-P10). Iberian atlantis has a greater tendency to white on P9 (40.3% vs. 22.5%) and less tendency to black on P6-P10 (61.6% solid vs. 86.6% solid).
4. cantabricans is strongly differentiated from Iberian atlantis and Southern atlantis on two of the four parameters available (P9, P6-P10). cantabricans has a greater tendency to white on P9 (84.6% vs. 40.3%; 84.6% vs. 22.5% respectively) and less tendency to black on P6-P10 (0.0% solid vs. 61.6% solid; 0.0% solid vs. 86.6% solid respectively).
5. argenteus is strongly differentiated from Iberian atlantis and Southern atlantis on three of the four parameters available (P9, P6-P10, P5). argenteus has a greater tendency to white on P9 (90.0% vs. 40.3%; 90.0% vs. 22.5% respectively) and lower tendency to black on P6-P10 (0.0% solid vs. 61.6% solid; 0.0% solid vs. 86.6% solid respectively) and a black band on P5 (73.9% absent vs. 17.3% absent; 73.9% absent vs. 24.7% absent respectively).
6. Camargue michahellis is strongly differentiated from SW Spain michahellis and atlantis/michahellis intersection on one of the three parameters available (P9). Camargue michahellis has a greater tendency to white on P9 (100.0% vs. 40.4%; 100.0% vs. 32.1% respectively).
7. Camargue michahellis is strongly differentiated from cantabricans and argenteus on two of the three parameters available (P5, P4). Camargue michahellis has a greater tendency to a black band on P5 (0.0% absent vs. 31.3% absent; 0.0% absent vs. 73.9% absent respectively) and black on P4 (55.7% vs. 10.0%; 55.7% vs. 0.0% respectively).
8. Azorean atlantis is strongly differentiated from cantabricans and argenteus and weakly differentiated from Iberian atlantis on the only parameter available (P9). Azorean atlantis has a lower tendency to white on P9 (13.0% vs. 84.6%; 13.0% vs. 90.0%; 13.0% vs. 40.3% respectively).

1. cantabricans is only weakly differentiated from argenteus on one of the four parameters available (P5). cantabricans has a slightly greater tendency to a black band on P5 (31.3% absent vs. 73.9% absent).
2. Southern atlantis is rather weakly differentiated on small sample sizes from both SW Spain michahellis and atlantis/michahellis intersection on two of the four parameters available (P5, P4). Southern atlantis has a slightly greater tendency to a black band on P5 (24.7% absent vs. 5.9% absent; 24.7% absent vs. 7.4% absent respectively) and black on P4 (9.0% vs. 50.0%; 9.0% vs. 50.0% respectively).
3. Iberian atlantis is rather weakly differentiated on small sample sizes from both SW Spain michahellis and atlantis/michahellis intersection on one of the four parameters available (P4). Iberian atlantis has a slightly greater tendency to black on P4 (14.3% vs. 50.0%; 14.3% vs. 50.0% respectively).
4. The two Southern atlantis populations compared (west Canaries, east Canaries) are weakly differentiated on one of the four parameters available (P6-P10). The west Canaries population has a slightly greater tendency to black on P6-P10 (96.2% solid vs. 80.5% solid).

1. SW Spain michahellis and atlantis/michahellis intersection are not differentiated at all.

If we take strong differentiation on at least two parameters as indicating significant overall divergence in wingtip pattern then we have the following groupings:

1. Southern atlantis, SW Spain michahellis, atlantis/michahellis intersection
2. Iberian atlantis, SW Spain michahellis, atlantis/michahellis intersection
3. cantabricans, argenteus
4. Camargue michahellis, SW Spain michahellis, atlantis/michahellis intersection

This indicates that the michahellis in the extreme west of their range have a tendency towards an atlantis wingtip pattern although structurally they are much more like the michahellis in the Camargue. This was also a finding of Dwight (1925) in his treatment of L. cachinnans. The extreme western michahellis also have sufficient similarity to the Camargue michahellis that they can be grouped with them as well. It is not surprising that the forms found at the intersection of atlantis and michahellis have affinity to both of them.

Another clear conclusion is the similarity of cantabricans and argenteus, raising the intriguing possibility that cantabricans is a Herring Gull. The range of argentatus includes yellow-legged populations so inclusion of cantabricans in the argenteus group should not be dismissed.

© Copyright Nick Rossiter 2002.