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Subject: Skua identification! [Print This Page]

Author: kkoel Time: 26/08/2009 13:28 Subject: Skua identification!

I would very much appreciate any comments on the species/age of these Skuas - please correct me if I'm wrong with the following:

*1: Arctic Skua, black morph, adult(?)
*2: Pomarine Skua, black morph, adult (despite sharp tail streamers?)
*3: Arctic Skua, pale morph, adult
*4: Arctic Skua, pale morph, juvenile (despite double crescent on underwing?)

Hokkaido, Japan
19/8/09

Thank you for reading and comments!

[ Last edited by kkoel at 26/08/2009 13:36 ]

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Author: cmichaell Time: 29/08/2009 13:25

Dear Koel,

All your pics are of Arctic Skuas. On shape and size they all have relatively long slender bills [Pomarine is heavier], long slender wings with the hand as wide as the arm [Pomarine has broader arms], and lack the thick-necked/barrel-chested/pot-bellied appearance of Pomarine. Where pointed tail feathers are visible on Bird 3, these are diagnostic of Arctic.

For ageing, note all pics taken mid-August in Japan. At this time, adults would still be in summer plumage as their moult does not begin until later in autumn, and you would expect to see juveniles moving south with older birds.

Birds 1 and 2 are both dark phase juveniles. They have pale bills with dark tips which shows they are not adult, and either no tail streamers [Bird 1] or only the beginnings [Bird 2]. They do not have distinct unfirm dark caps and have paler neck bands [esp Bird 1] which are typical of juveniles.

Birds 3 and 4 are older. Bird 3 is pale phase whereas Bird 4 is intermediate. Both have plumage patterns close to adults with distinct dark caps and pale collars. However, their underwing coverts are not uniformly dark and they appear to have pale bases to the bill, both indicators of younger birds. Also from above they have paler upper tail coverts which again is a sign they are not yet adult summer [note adult winter birds have paler uppertails, but as noted above it is too early for adults to be in winter plumage]. Bird 3 has distinct pointed tail streamers which are well developed but not yet full length. Bird 4 shows no tail streamers - perhaps they have been broken. I consider both to be second summer. They are not first summer which is much more like juvenile and would show contrasting ages of feathers on the wing at this time of year.

Hope you enjoyed the trip. The Hokkaido ferries are a great way to see a wide variety of north Pacific seabirds.

Mike Chalmers

Author: kkoel Time: 30/08/2009 18:58

Dear Mike,

Thank you very much for your comments! On the same trip were some more Pomarine Skuas, a Pacific Diver, Spectacled Guillemots, and Rhinoceros Auklets.

I have one more question in mind: I also noted several Skuas in an inland lake in central south Hokkaido (Lake Akan). Do you know if Skuas migrate over land occasionally? There did not seem to be a storm nearby, but would widespread rain and dense fog over NE Hokkaido have been enough to mislead some skuas inland?

Koel

Author: tmichael Time: 30/08/2009 21:41

They are certainly known to migrate regularly across the British mainland, leaving the North Sea and then basically flying along the England-Scotland border, before entering the Solway Firth and proceeding south down the Irish Sea.

Mike Turnbull

Author: cmichaell Time: 30/08/2009 23:26

Dear Koel,

All the Stercorarius skuas [Pomarine/Arctic/Long-tailed] are regularly seen inland. Many make huge overland migrations to reach their arctic breeding grounds. Remember also that the first skua record in Hong Kong was flying inland from Mai Po. On migration, skuas will seek out gulls and terns for food and I would guess your birds at Lake Akan, which isnt far from the coast, were there because of prey potential [or even a fresh water wash] and not adverse weather.

Mike Chalmers

PS. Another point I forgot to mention on ageing your pics are the distinct pale legs seen on one of your juveniles whereas adults have black legs. Note all ages have black feet.

Author: kkoel Time: 1/09/2009 18:51

Thank you Mike & Mike! I used to think the inland records are accidental: thanks for rectifying that. =)

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