Good news for gannet fans

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In some respects, the 25-kilometre stretch of Fare­well Spit is the last place you would expect to find a colony of gannets. Else­where in the New Zealand biological region the birds characteristically choose craggy offshore islands to build their mounded nests of seaweed, soft plants, earth and guano. Of these 20 or so colonies, the Cape Kidnappers site has been a very viewable mainland exception, while the rock stack of Motutara at Muriwai also provides reasonable viewing from the shore.

Farewell Spit is home to over 90 species of birds, so it isn’t surprising that a few gannets have made an appearance on the orni­thologist’s record sheet, along with kea, sparrows, spoonbills and a veritable who’s who of waders. A census of gannets taken in 1946-47 recorded some 21,000 pairs breeding in New Zealand, a number which doubled to 43,000 in a 1980 reassessment. Together with non-breed­ing roosters a likely popu­lation of some 90,000 adults can be deduced today.

Such a successful breeding pattern gives no surprise to the fact that from 300 birds recorded on Farewell Spit in 1983 there are now over 900 nesting sites. But what is surprising is where they have chosen to nest: three adjoining hillock-like sandy shellbanks two kilometres past the lighthouse. The establishment of this second mainland colony represents a departure from their preferred craggy headland roosts.

The Australasian gannet (Sula serrator) lays its single egg between Septem­ber and December. Incuba­tion is shared by the parents for the 43 days before the black and naked chick emerges. Within a month the chick’s plumage is fluffy white, but it later changes to a brown-and­white mottle—the juvenile coloration. By May most of these juvenile birds have left the Spit to begin their flight over the Tasman. They will spend anywhere up to three years around the Australian coast south of Queensland before returning to New Zealand to breed.

Although some will begin breeding as early as their fourth year, most will wait until their fifth year, or even later. Gannets form strong pair bonds with a lifetime partner.

From August, a wonder­ful procession can be observed on the Spit as the males fly down to the high tide mark in front of the lighthouse to gather their nesting material. Debris, seaweed and marram grass are plucked up, then the birds circle around the foreshore before returning to their nests. Observers have likened the manoeu­vre to aircraft in a holding pattern: individual birds collect their cargo, then take up their position in what looks like an endless circular conveyor belt before shuttling back to their nests one by one.

The females stay to guard their sites—a neces­sity, given that unattended nests are raided and even wholly dragged away by opportunistic males. Sandy grit and faeces are the cement which holds the building materials together, and the final structure is a substantial bowled nest positioned a metre or so from its neighbour—just out of pecking range!

Why have these gannets chosen this unusual nesting site? Certainly, other colonies are under severe population density pres­sure as numbers increase and nesting sites become scarce. A 1987 survey reported the Spit popula­tion to be composed of mainly younger birds. In established colonies these individuals would be working hard to establish territory, and would often end up as fringe dwellers. Farewell Spit offers an almost unlimited number of sites and an extended feeding range through 360 degrees.

As a result of migration to the Spit, the birds have become a common site in Golden Bay, gliding across the water, then plummet­ing into the sea from heights of up to 30 metres to take sprats, squid and school fish. For anyone who has wondered how their bodies can withstand the crushing impact with the water when they dive, their 145km/hr entry is cushioned by inflatable air sacs beneath the skin on the lower neck and breast.

Because public access to the Spit is under strict control (the area has been designated a wetland of international importance).