South Polar Skua Stercorarius maccormicki
Two records, both presumably juveniles/first years: the first about 20-25 Km south of Busan shore (November 4th 1995) - presumably (and according to the hydrofoil staff) this was still in Korean waters; the second (of 1 or 2 birds), about 4 km east of Gageo Island, Jeollanam Province (October 20th, 2001).
The first South Polar Skua was observed from the Busan-Fukuoka hydrofoil, when it flew very close to and then across the vessel. Observations were made over 20-30 seconds in good light through 10x40 Nikon binoculars. Identification was based, in direct comparison with a Pomarine Skua, on (1) its overall bulkier appearance, and (2) the whole plumage being washed through with browns. (3) The palest area was on the hindneck, with (4) the upperparts darker than the underparts. (5) The upperwing showed obvious white on the upperwing, forming a distinctive double crescent (with limited white on the primary coverts with a more distinctive white blaze across the primaries).
The second bird was seen within 10 km of the eastern flank of Gageo Island on October 20th 2001, outside and from the rear of the Mokpo-Gageo hydrofoil, presumably attracted to a very large concentration of seabirds which included more than 500 Streaked Shearwater Calonectris leucomelas, a Swinhoe’s Storm Petrel Oceanodrama monorhis, a Brown Booby Sula leucogaster, 300 Black-tailed Gulls Larus crassirostris, 3-4 Pomarines and at least 2 other skuas too distant to be identified. It was watched for about 30 seconds through Leica 8x32 binoculars at a range of between 50-150 m, then followed as it flew to ca 500m range when it joined another bird which looked very similar in structure. Again, structure and plumage details were only noted in brief, however in near-direct comparison with a Pomarine Skua: (1) rather large and powerful, obviously more so than Pomarine Skua, with a structure and wing action intermediate between that and Great Skua Stercorarius skua, and somewhat suggestive of Slaty-backed GullLarus schistisagus; (2) short-ended, lacking an obvious tail projection; showing (3) a very strong white flash across the primaries, with a smaller, thinner white crescent across the primary coverts (this pattern has been noted on many of the 200 or so South Polar Skuas seen from the Tokyo-Kushiro ferry in Japan by NM during the 1990s): (4) a paler collar contrasting with darker upperparts and grey-brown underparts.
Identification to species of this complex is far from simple, but separation from potentially vagrant Great Skua was based on (1) the smaller size and lighter build of South Polar, and (2) the lack of streaking on the upperparts; and from Great and other Stercorarius/Catharacta skuas by (3) the presence of an obvious pale collar, a feature considered diagnostic of South Polar Skua by Harrison (1983).
Although previously unrecorded in Korean waters, juvenile South Polar Skuas are known to "undertake a regular migration into N. Pacific and Atlantic Oceans…some may remain throughout year" (Harrison, 1983). It is therefore thought to occasionally pass through the South China Sea (MacKinnon and Phillipps, 2000) and is regarded as an uncommon spring and summer migrant in Japan (Brazil, 1991), with smaller numbers also present in winter. Although both records were in late autumn, the species might eventually prove to be more regular in spring or summer in Korean waters, attracted to flocks of shearwaters or storm-blown to within sight of land (Brazil 1991).