Monday, December 17, 2007

Orca whales hunt eider ducks for practice

Education time for young killer whales also means the hardest of lessons for eider ducks - or at least those surviving the experience.In pictures: Orca whales hunt eider ducksGrey seals are the main targets of orca pods venturing regularly into the inshore water of Scotland's Northern Isles but isolated attacks on groups of swimming eider have also been noted in recent years.One of the orca whales approaches the ducks to herd them towards the younger whalesThis happens during the late summer period when these largest of UK sea ducks can't take to the air through moulting their flight feathers - so making them vulnerable to one of the fiercest of marine predators.But why should huge hunters, averaging around eight metres long and weighing up to 7,200kgs (eight tons), with big appetites - even in captivity they eat 45kgs a day - bother with comparative small fry?One answer became obvious to leading UK wildlife photographer Hugh Harrop after a phone alert led to him dashing around 20 miles from his home near Maywick on the west coast of mainland Shetland.He reached Gulber Wick, near the Shetland capital, Lerwick, on the east coast just in time to see the tall dorsal fins of a five-member orca pod heading into the deep bay - towards a flock of 100 eider."Immediately the eider sensed danger and formed into a defensive pack - almost a solid raft of birds", said Harrop. "That was a big mistake - had they scattered widely it would have been harder for the orcas."At this point two adult whales, accompanied by a calf, split from the pod and began a manoeuvre that was clearly intended to herd the eider towards two older youngsters with them.The ducks tried to escape but, flapping their flight featherless stumpy wings, could do no more than run across the water's surface - and the two immature orcas began seizing and swallowing them one-by-one."I gained a distinct impression they were not hunting the eider because they were hungry", Harrop added. "Instead it seemed as if the adults were teaching the two immatures how to catch prey."Had they needed a square meal there were grey seals in the bay but these were ignored totally. Also, they could have caught all the eider if they'd wanted but after taking 30 - 40, they stopped. A whale near the terrified ducks (top) and one of them bashing their tail with joy"After that they just played around."They smashed their tails down on the surface, one rolled around on its back, then finally one of the youngsters stuck its head right out of the water as if to say goodbye."It was an extraordinary experience for me."This was one of the very few times orcas have been seen attacking eider flocks in the UK and probably the first time this awesome behaviour has been photographed here."The first documented account of Shetland eider being attacked by orcas came almost exactly two years earlier - in Bressay Sound, just north of Lerwick. Forty eider were eaten in just five minutes on that occasion.Later, in a report in the journal British Birds, Martin Heubeck, an Aberdeen University zoologist monitoring Shetland seabirds, pointed out such attacks could have serious implications for local eiders.He said Shetland's eider population - the latest estimate was 5,100 based on counts of moulting flocks - had fallen by 60 per cent during 1977-91 and since then by a further 27 per cent. The most recent decline seemed gradual, about two per cent annually"However, it may well accelerate if such behaviour by the pods of killer whales that cruise close inshore during summer becomes more frequent, taking almost one per cent of the total population in just five minutes."Information appearing on

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