Thursday, April 12, 2012

South Polar Skua at Bremer Bay

An intermediate-morph South Polar Skua (Catharacta maccormicki) was observed around the Bremer Bay area over the Easter weekend, from Saturday 7th April 2012 until at least Monday 9th April. Authenticated sightings of this species are extremely rare in Australia, particularly Western Australia, and even these records are typically pelagic or offshore, making this sustained inshore sighting most unusual.

The bird was first seen distantly on the afternoon of 7th April, harassing Crested Terns and Silver Gulls around the rocky point and offshore island east of the Fisheries harbour (end of Swarbrick Rd) at Bremer Bay. Its contrasting pale head and neck, and relatively small size raised suspicions of South Polar Skua, but unfortunately this could not be confirmed before the bird disappeared.

South Polar Skua at Bremer Bay.



By an incredible stroke of luck, the bird was relocated early the following morning (Sunday 8th April), paddling calmly in a small rocky bay at the southernmost end of Bremer Beach (end of Bremer Bay Rd). It appeared untroubled as this series of photographs was taken from a distance down to only 5 metres or so, before it flew off south over the headland. The bird was seen again the following evening (Mon 9th), once again closely harassing the Crested Terns roosting on the rocks immediately east of the Fisheries harbour groyne.



South Polar Skua taking off at Bremer Bay. Note contrast between the dark underwing and paler belly.

This is believed to be only the 4th or 5th sight record in addition to the single WA Museum specimen, found dead at Rockingham in June 1994 [1]. HANZAB [2] lists records off Geraldton (Nov 1980), and several sightings around Albany in May 1986, including an intriguing record of nine birds at The Gap, though WA Museum’s Handbook [1] regards these sightings as unconfirmed. A probable bird seen on the August 2004 Hillarys Pelagic was not accepted by BARC (Case 440), largely due to lack of a photograph.

The seemingly settled, inshore behaviour of this individual is intriguing, given that it should be on passage to its far northern wintering grounds. South Polar Skuas (unlike locally overwintering Brown Skuas), are long-distance trans-equatorial migrants that winter in the northern Atlantic and Pacific oceans, as well as the Indian Ocean where its movements are less well known [2]. Given the unpopulated and inaccessible nature of much of WA’s southern coastline, this raises the interesting possibility that South Polar Skuas may occasionally visit WA’s far south coastline this time of year as a ‘refueling stop’ before continuing their northern passage, presumably into the Indian Ocean.

The Bremer Bay South Polar Skua posing co-operatively for photos!

The photographs of the bird clearly show key indentifying features of intermediate-morph South Polar Skua:
• pale and ‘cool-toned’ grey-beige head, neck and belly, palest on the nape, contrasting with the dark brown-black upperparts and underwing
• relatively homogenous upperparts, lacking the pale mottling of Brown Skua, with pale streaks or fringes limited to the scapulars and most heavily-worn coverts
• comparatively smallish head and slender neck
• relatively slender bill, with a modest unguis and an inconspicuous and short gonys (Olsen & Larsson [3] suggest the criteria for gonys of 30-40% of total lower bill length for South Polar, versus 40-50% for Brown Skua – this bird is around 35%)


Good corroborating features include the bird’s relatively small size and less bulky appearance as noted in the field, and the timing of the moult, which fits nicely for South Polar [3]. The extent of the white primary panels can be a useful feature but in this case is intermediate, so non-diagnostic.

Bremer Bay South Polar Skua in flight.

NOTE: The identification of this bird should be regarded as provisional until accepted by BARC. This bird has now been accepted by BARC


UPDATE: The bird was been seen again Sat 14th April around 4.30pm, again around the Bremer Bay Fisheries harbour area, in the company of some noticeably larger Brown Skuas [Nigel Jackett and Stewart Ford per birdswa mailing list]. I think that makes this Australia's first ever twitchable South Polar Skua!

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References
[1] Johnstone & Storr (1998). Handbook of Western Australian Birds Volume 1: Non-passerines. WA Museum.
[2] Higgins PJ & Davies SJJF (1996) Handbook of Australian, New Zealand & Antarctic Birds, vol. 3: Snipe to Pigeons. Oxford University Press.
[3] Olsen KM & Larsson H (1997) Skuas and Jaegers. Pica Press.

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