We (Dick Newell, Richard Porter and Tony Marr) first published our Senegal findings in Birding World magazine Vol 10 Number 6, June 1997. Some of the pictures here were also in that paper. We then concluded, on the knowledge that we then had, that all of these birds were South Polar Skuas Catharacta maccormicki.
Some experts largely agreed with our conclusions, but there were also reservations – suspicions ranging from Great Skua C. skua to Brown Skua C. antarctica without necessarily preferring any of the three South Atlantic forms: nominate, hamiltoni or lonnbergi (not to mention hybrids).
Many of the Senegal birds are black. Dark phase Great Skuas make up between 10% (Olsen and Larsson) and 30% (Bearhop, Furness and Zonfrillo, BW Vol 11 No 9, Sept 1998) of juveniles (field observations in Spain indicate a much lower proportion of dark birds - Daniel Lopez pers comm.).
Since 1995, we have seen several hundred large skuas off Dakar including only 1 possible juvenile pale phase Great Skua and nothing resembling an adult. So, even if many of these dark birds could not be identified as individuals, statistically it is unlikely that they are all dark phase juvenile or immature Great Skuas.
Jiguet, in a follow-up paper to ours, containing excellent pictures (BW Vol 10 Number 8, August 1998), highlighted the difficulties of separating South Polar from Brown Skua, but we now think that a pure Brown Skua so far north would be extremely rare..
In Senegal, we saw a few birds birds that could match 1st cycle, as well as many older dark, intermediate and light phase South Polars.
Some of the Senegal skuas have pale streaks and scallops on the scapulars, without pale marks on the wing coverts, forming a pale saddle, quite unlike the coarse streaking on a Great Skua. This is diagnostic of a southern hemisphere skua.
Whereas it is quite possible that there are Brown Skua genes is some of the individuals presented here, we do not think that this undermines our assertion that large numbers of South Polar Skuas move south past Senegal in October.