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Gannets and boobies

by  Maggy Wassilieff

In an astonishing first flight, young gannets leave New Zealand and travel nearly 3,000 kilometres to Australia. Those that make it back seldom repeat the journey. Gannets have established huge coastal colonies where they breed and feed, catching prey with the deadly accuracy of their trademark plunge-dive.


Gannets: description and habitat

There are three gannet species worldwide, all with adults similar in appearance.  The northern gannet (Morus bassanus) is a North Atlantic bird which does not venture into southern waters. The African Cape gannet (Morus capensis) appears infrequently in Australian and New Zealand waters. It is recognised by the long black stripe on its throat and a completely black tail. The Australasian gannet (Morus serrator) is found in Australian and New Zealand waters.

Fake it till you make it

In 2008 decoy gannets made of concrete were used to entice Australasian gannets to breed in a pest-free enclosure on Young Nick's Heard, near Gisborne. An audio system played gannet colony sounds as further encouragement. The experiment was a success, with birds returning year after year and fledging chicks.

Description

With its 2-metre wingspan, golden head and dramatic plunging dives, the white Australasian gannet is an easily identified seabird. Adult gannets are about the size of a goose, with black-tipped wings, black central tail feathers and a strong, conical blue-grey beak. Juvenile birds look quite different. In their first year they have speckled brown feathers on their upper body, and white undersides. Each year more white feathers appear on their backs, and the birds acquire their adult appearance by five years of age.

Population

Australasian gannet numbers in New Zealand increased markedly during the second half of the 20th century – from an estimated 27,000 breeding pairs in the first census of 1947, to 46,000 in the 1980–81 count. New Zealand is home to 87% of the total population of adult birds.

Tākapu treasures

Māori made expeditions to the rocky breeding grounds of gannets, or tākapu, catching the young birds for food and the adults for their bones and plumage. Bones were fashioned into chiselling tools and used for applying elaborate facial moko (tattoos). The valuable white feathers were used to decorate canoes, or were worn by high-ranking individuals.

Location

New Zealand is one of the best places in the world to view Australasian gannets. There are three accessible mainland breeding colonies – at Cape Kidnappers, Muriwai and Farewell Spit.

There are also 21 offshore gannetries, and an expanding population. The largest breeding colonies are on the Three Kings Islands, Gannet Island, and White Island. The birds live all around New Zealand’s coastal waters, especially north of Cook Strait. They are also found around much of the Australian coast, including Lord Howe and Norfolk islands.

Cape Kidnappers

Gannets usually breed in colonies on offshore islands. However, in 1880 a New Zealand naturalist, Henry Hill, noted that about 50 gannets had started breeding on an elevated headland at Cape Kidnappers in Hawke’s Bay. The area was protected as a reserve in 1915 and the gannet population steadily increased. By the late 1990s there were 6,500 breeding pairs in four sub-colonies. For nearly a century Cape Kidnappers remained the only mainland colony in New Zealand.

Muriwai

In the 1980s a colony established itself north of Auckland at Muriwai Beach. Two headlands were fenced off to protect nesting gannets that had arrived from nearby Motutara Island. However, the fences eventually prevented the colony from expanding. Once they were removed, in 1996–97, the population more than doubled within four years.

Farewell Spit

Unlike the Cape Kidnappers and Muriwai colonies, which are on elevated sites, the most recently established colony is practically at sea level. The birds breed on shell banks at Farewell Spit, at the north-west tip of the South Island. Beginning with 75 breeding pairs in 1983, the colony grew to around 600 pairs by 1987. The site is vulnerable to storms; the colony was nearly wiped out in January 1997 by Cyclone Drena, but eventually recovered.


Gannets: life history and feeding

Chicks

Females lay a single pale blue egg, the size of a large hen’s egg, any time from mid-September till mid-December. It is laid in a nest prepared from dried seaweed cemented with guano (bird droppings), and incubated by each parent in turn. After 43 days a blind, naked chick hatches, and is fed and cared for by both parents.

The chicks grow rapidly. In the first week they develop white fluffy down, which is replaced during their second and third months by juvenile plumage. By 14 weeks the chicks weigh 3 kilograms, half a kilogram more than the parents, and they begin flapping and stretching their wings for hours each day. Then suddenly in their fourth month of life they take off, not to return for several years. Their destination was a mystery until the 1950s, when juvenile birds were first ringed and tracked: they turned up in coastal waters around the east coast of Australia.

Trans-Tasman flight

Without any previous flight practice, without having had to seek out their own food, and without any accompanying adults, the fat young birds fly 2,740 kilometres across the Tasman Sea to the east coast of Australia in late summer and early autumn. The journey takes 8 to 14 days, depending on the weather and wind direction. Juvenile birds remain in Australian waters for two or three years, and then return to their hatching site in New Zealand in early spring. The two-way journey is fraught with dangers – including storms and predators – and there is a high mortality rate. In a good year, about a quarter of the birds manage to return safely to New Zealand.

Breeding

Most adult birds do not migrate. Once back in New Zealand they spend spring and summer at the breeding colony and then disperse around local coastal waters for the winter months. Birds newly arrived from Australia may not be able to claim a nest site or a mate in their first couple of years back at the gannetry, but once successful, they mate for life and may survive for 30 years.

Diving for prey

Westward a gannet dived in a fire-white streak
Straight to the waters, and so was gone like a stone. 1

Although ungainly on land, gannets are magnificent in flight. When searching for food they fly parallel to the coast, between 1 and 20 metres above the sea, looking for schools of fish or squid. They plunge headlong as soon as they spot their prey. Just before they hit the water, they fold in their wings to swoop down beneath their food. They can enter the water at speeds up to 145 kilometres an hour, relying on inflatable air sacs around the neck and chest to absorb the shock of impact. They grab the prey in their beaks and swallow it whole once they have surfaced.

As good as a goose

Gannets make tasty eating, and have not always been protected by law. Māori used to harvest the young, and at Christmas in 1769 the naturalist Joseph Banks, on board the Endeavour with Captain James Cook, made these entries in his diary:

‘24. myself in a boat shooting … killing cheifly several Gannets or Solan Geese … As it was the humour of the ship to keep Christmas in the old fashiond way it was resolvd of them to make a Goose pye for tomorrows dinner.

‘25. Christmas Day: Our Goose pye was eat with great approbation.’ 2

Food

A gannet will often regurgitate its stomach contents if disturbed or handled; if the bird has recently fed, the prey can be identified. Small fish such as pilchards, anchovies, saury, jack mackerel and squid form the basis of the gannet diet. One of the theories advanced for the dramatic increase in New Zealand’s gannet population is that inshore commercial fishing has reduced the number of large predatory fish, resulting in a corresponding increase in small fish. This abundance of food for adult gannets enables more chicks to survive.

Present status

Australasian gannets are totally protected by law, and the New Zealand population is in a healthy state. However, gannetries are susceptible to the effects of oil spills, and the birds have been caught in set nets or on the lines of recreational fishermen. Adult and young birds can become entangled in the rope ties from nearby mussel farms, which they incorporate into their nests. Mainland colonies are vulnerable to egg predation by black-backed gulls following human disturbance.

Footnotes
    • Robin Hyde, ‘Montaigne on the hillside.’ In Young knowledge – the poems of Robin Hyde, edited by Michele Leggott. Auckland: Auckland University Press, 2003, p. 83. › Back
    • Joseph Banks, Journal (South Seas project, 2004), 24 and 25 December 1769, http://nla.gov.au/nla.cs-ss-jrnl-banks-17691224 and http://nla.gov.au/nla.cs-ss-jrnl-banks-17691225 (last accessed 31 May 2005). › Back

Masked boobies

Like their close relatives the gannets, boobies belong to the Pelecaniformes order and are strictly marine birds, only coming ashore to breed and nest. But unlike gannets, they are birds of the tropics and subtropics. Only one species, the masked booby (Sula dactylatra), breeds in New Zealand, but brown boobies (Sula leucogaster) regularly occur as vagrants, as far south as Nelson.

Distribution

Around 200 pairs of masked boobies breed on the Kermadec Islands, New Zealand’s northernmost offshore group, 700 kilometres north-east of North Cape. Masked boobies are also found breeding on islands belonging to Australia – Lord Howe, Norfolk, Nepean and Phillip islands.

Once numerous, masked boobies were nearly hunted to extinction on Lord Howe Island and Norfolk Island. Today, longline fishing poses a threat to birds at sea.

Sitting ducks

It is believed that the word booby comes from the Spanish ‘bobo’, meaning a dolt, or stupid person. The term was used for large seabirds that were easy to kill.

Description

At a distance, masked boobies resemble white-headed gannets. Named for their mask-like facial skin, which is blue-grey, they are the largest of the boobies – nearly 1 metre long and with a wing span of 1.5 metres. The sexes are similar in size and appearance, although males typically have a brighter yellow bill than females. Adults have white bodies and dark brown-black flight and tail feathers. Juveniles have greyish-brown upper bodies and a grey bill.


External links and sources

More suggestions and sources


How to cite this page: Maggy Wassilieff, 'Gannets and boobies', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/gannets-and-boobies/print (accessed 9 December 2019)

Story by Maggy Wassilieff, published 12 Jun 2006, reviewed & revised 17 Feb 2015