Sunday, March 11, 2012

Our World/outdoor Wed: gannets

We often travel west from Auckland to Muraiwai beach to see the gannet colony. Australasian Gannets migrate from the north to nest in dense colonies on small islands and jutting cliffs with most being in the North Island of New Zealand.

In 1979 the Auckland Regional Council (then ARA) established the Takapu Refuge with the help of the Royal Forest and Bird Protection Society.

Gannets come in early spring. The males usually arriving first. After breeding and once the chicks have fledged and left the nest, they fly north. The mature adult birds tend to be sedentary, only fishing over inshore sea close in to the coast.

It's a tough life being a gannet.

Not only do they have to travel up to 500 kilometres a day and fight off o 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 autopsies 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.

These photos are posted specially for Eileen, I had wanted to show off our cliffs for so long.


Indrani said...

There is a fight for survival everywhere.

Light and Voices said...

Thought provoking.
Joyce M

momto8 said...

oh for this....I love to learn something new everyday!
I am your newest follower..pls follow back if you an.

Magia da Inês said...

Belas paisagens.
Bom dia!
♪º° ✿

eileeninmd said...

Hi Ann, great post on the Gannets. And I love the photos of the cliffs. New Zealand is a gorgeous country. Thanks for sharing the link and for doing your cliff post. Have a great day!

Zenserly said...

those cliffs are beautiful...