Deep study of the gannet collision zone

MICHAEL FOX
Last updated 09:55 09/03/2012
Earth-Touch

Gannets join sharks and dolphins underwater to hunt fish, but what happens when the birds collide?

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It's a tough life being a gannet.

Not only do they have to travel up to 500 kilometres a day and fight off other predators like dolphins and sharks to feed on fish, new research shows they're killing themselves in the process.

New underwater footage of gannets diving for fish has revealed the birds sometimes pierce the necks and heads of other birds as they dive at high-speed for a feed.

The study by Massey biologist Gabriel Machovsky Capuska has also revealed the birds are not above stealing from each other, as footage shows them burgling fish from the beaks of others who have already done the hard work.

Machovsky Capuska has been studying the foraging and feeding behaviour of the Australasian gannet Morus serrator, in the Hauraki Gulf and at Cape Kidnappers and Farewell Spit.

The Argentinean scientist believes that while the gannet is familiar to many New Zealanders, few people are aware of gannets' "amazing physiological capabilities needed to survive".

Machovsky Capuska says the birds fly up to 500km in a day in search of shoals of pilchards and anchovies.

Once found, they plunge-dive from 15 metres, dive to about 20m and spend up to 42 seconds underwater pursuing prey amongst heavy traffic in what he says is a generally successful strategy.

"Equipped with extraordinary vision, they can adapt their optical capability in a split second from air to water while effectively blocking out ultraviolet light reflection that distorts the position of darting prey."

The fatal collisions occur during high-density feeding, when two gannets target the same fish and one pierces the neck or head of the other.

Machovsky Capuska said post-mortems of two of 50 carcasses collected from Hauraki Gulf waters showed the gannets had died from collision injuries.

"While this ratio suggests the phenomenon to be relatively rare, analyses of underwater video footage of Cape gannets in South Africa shows accidental collisions between gannets are not so uncommon."

The footage also captured evidence of kleptoparasitism, or parasitism by theft, where a diving gannet targets a previously caught fish in the beak of another gannet underwater.

The study will be completed later this year.

Machovsky Capuska said that understanding of the anatomy and physiology of gannet necks could have implications for understanding the dynamics of neck injuries in humans who dive.

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