Gannets: demon divers

Sep 19, 2017 Environment

A bird bombardment rekindles memories of Alfred Hitchcock’s classic movie for Lindsay Wright. Photos by John Eichelsheim and supplied.

Watching takapu/gannets at work, it’s easy to imagine being in the front lines of a mediaeval battlefield when enemy archers let fly with their arrows. Even their Latin name – Morus serrator – has a sharp abrasive edge to it.

High-speed, feathered projectiles plummet from the sky all around the boat as streaks of yellow-headed gannet, travelling too fast for the eye to follow, hit the surface with a sizzling rush and disappear underwater.

Straight away the scenes from Alfred Hitchcock’s 1963 horror thriller The Birds spring to mind. In the movie, flocks of aberrant birds terrorise a small American town. Locally, though, our gannets are focussed on food – schools of pilchards, anchovy or jack mackerel.

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The feeding boot was on the other foot when Captain James Cook’s HMS Endeavour first came across the Three Kings Islands on the 24th December, 1769. With Christmas just a day away, her crew were also focussed on food – an English-style, slap-up Christmas dinner in this strange land where the summer sun shone brightly at Yule time.

Nearby gannets fell foul of the sailors’ guns, because of their resemblance to solan geese – northen gannets – from the English homeland. “On 25th December, Christmas Day, our goose pie was eaten with great approbation,” botanist Sir Joseph Banks noted. “By evening all hands were as drunk as our forefathers used to be upon like occasions.”

You’d imagine a gannet pie would have a strong fish flavour – but no mention was made of it, so maybe inebriation helped make the dinner go down – or perhaps, after months on RN rations, anything tasted good.

The British matelots had misnamed their dinner. The Australasian gannet, in fact, belongs to the family Sulidae and is related to shags, pelicans and (this will get the primary schoolers giggling) tropical boobies.

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Unlike other native seabird species, gannets are flourishing and breed at 28 colonies around our coastline. The nearest to Auckland are Gannet Rock near Waiheke Island, the new colony at Motuora and the 2,500 or so pairs nesting at Mahuki Island in the Broken Islands on the west coast of Aotea/Great Barrier. But the biggest colonies are at Gannet Island, Kawhia and White Island in the Bay of Plenty.

The gannets’ practice of breeding on offshore islands has removed them from the range of the common predators that have decimated other seabird populations. It’s estimated there were 325 pairs at Mahuki Island in 1946 but ornithologists say there may be a return to pre-human population numbers since gannets became protected in 1924. Scientists say numbers are now increasing by about two percent per annum.

To be among feeding gannets is to experience an intermingling of awe, fear and wonder. The birds sweep down from about 30m and skim the wave tops. They climb back to diving height, wheel and plunge, reaching about 145km/h velocity before piercing the sea, leaving barely a ripple to mark their passage. Hundreds – or even thousands of the elegant 2.5kg birds – hit the water at high speed within centimetres of each other.

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A network of air sacs on their lower neck and breast inflates to take the pressure of sudden immersion and the long, high-aspect 90cm wing span is folded back but extended once they’re in the water. Combined with their big, webbed feet, these can power them down to 43m in pursuit of prey.

Another adaptation to tackle this lifestyle is the long, sharp grey beak. I once heard that older gannets go blind due to repeated dives and starve to death. Still, they are one of the longest living seabirds – all three of the gannet species live to 25-38 years and mate for life.

The guano-speckled nesting colonies are deserted from autumn to early winter until, depending on location, late July, when the first gannets arrive. They exchange fronds of seaweed (prime nest-building material) and perform a raucous dance to show ownership of the nesting site – proof of their ability to raise chicks.

When the female arrives, she settles in at home and a single egg is laid. Unseasonal cold spring weather has been known to wipe out a generation of gannets but they can lay another egg to compensate.

About 14 weeks after hatching, the chick has lost its fluffy plumage and, gorging on food regurgitated in turn by both parents, it weighs in at about 3kg. Or 500g more than its parents.

At four months old, time has come to leave home and the young gannet soars off on its first ocean passage – 2,800km to Australia. They’ve been recorded from Queensland as far south and west as Fremantle, feeding in coastal waters before they answer the call to breed back in Aotearoa. At between three and five years old they wing home across the Tasman and claim a nesting site to begin breeding.

Like a lot of seabirds and fish species these days, the peril comes from plastic flotsam which tangles in the gut and starves the birds to death – or mechanised factory fishing competing for the same food stocks.

But the sight of great clouds of gannets, plunging from the sky in frenzied feeding mode to graze on school fish is one of the most exciting things you’ll see at sea.

Long may it last.