The Birds of Great Barrier Island

Environmental News Issue 6

Many of the referendum forms highlighted the need for more information on Great Barrier Island’s endemic birds. John Ogden, Associate Professor of Ecology at Tamaki Campus (AU) illuminates the subject and invites those of you interested in ‘hands on’ ecology to participate...

The Trust has recently received some funding to gather base-line data on the birds of Great Barrier. While there is detailed information for some species, such as brown teal and black petrel, for the majority of species nothing is known about their current population sizes, nesting success or trends over time. Moreover, much of the available data are hidden in Department of Conservation Reports, or obscure publications, so that getting an overview picture is difficult. The excellent general account by Tim Lovegrove in "Great Barrier Island" (Armitage 2001) does not discuss numerical aspects. Recent events, such as the influx of bellbirds following rat eradication on Little Barrier, and the recent introduction of robins to two locations on the island, have highlighted the need to better integrate the information available and to set up a system for monitoring change.

Before outlining the Trust’s proposals, I’ll provide some background. The total species checklist for Great Barrier stands at 111 species. This includes some species no longer found here, and some marine species only occurring on land as ‘beach wrecks’. Eightytwo of these are currently present, or at least are known to be occasional visitors to the island. This can be compared with 328 species known from the whole of the New Zealand region since 1995 - we have about a quarter of the total! Of the difference between the 111 which have been recorded, and the 82 now present, 11 are known to have gone extinct on the island since 1868, when Hutton visited the island and made a list. The remaining 18 are very rare visitors or of uncertain status. If the birds are divided according to main habitats we get the results in the table opposite.

Since Hutton’s list was made in 1868 the island has lost eleven bird species, predominantly from forest habitats. Stitchbird, saddleback, kokako and others can now be seen on the restored Tiritiri Matangi Island, but not on Great Barrier. Over the same time period the island has gained 25 introduced species. These are predominantly generalist European birds, such as sparrows and starlings, associated with people and inhabiting open areas. Clearly the shift in the landscape, from the forest of Hutton’s day, to the more open farmed landscape this century has resulted in massive changes in bird populations. In percentage terms we have lost 33% of our forest bird species, and many of those remaining, such as pigeon and kakariki, are in much smaller numbers than formerly. Meanwhile we have gained 74% of our farmland birds, flooding into the new man-made habitats.

In contrast, marine and coastal environments appear to have suffered little change. This however may not be quite as it seems, because we have almost no data on some species. Mostly they’re only identified for sure when they’re washed up dead on a beach. As with many off-shore islands it is likely that Great Barrier once had huge nesting colonies of marine birds. Although many of these may have been exterminated before European contact, their loss may still be having its influence on other aspects of the ecology of the island through the loss of many tons of nitrates and phosphates formerly deposited as guano annually into the soil of the island. With the elimination of rats and cats from Little Barrier I anticipate that we’ll start to get more nocturnal visits from Cook’s petrels and other sea birds looking for nesting sites. However, unless we also eliminate cats, all we’ll see of them will be their disembodied wings on our bush tracks.

We have lost one coastal bird—the shore plover. The New Zealand Dotterel seems to be holding it’s population steady at c. 40-50 birds, but is still at risk from increased visitors, and their dogs, on the nesting beaches over Christmas. We have an interesting suite of waders visiting the Okiwi spit during migration: bar-tailed godwits and Pacific golden plover, and occasionally rarities such as whimbrel and large sand dotterel. Some of these species migrate to and from Siberia each year. In addition we have South Island visitors such as wrybills, banded dotterel and pied oystercatcher. Even our resident dotterels and variable oystercatchers seem to mostly go to Whangapoua for their winter holidays.

We are fortunate in still having one large wetland, Kaitoke Swamp, but unfortunately it, like the others, is inhabited by rats, cats and pigs. Despite that, it is the key site for fern-birds in the Auckland region. Other wetlands, such as those formerly behind the dunes at Awana, Claris and Medlands, have been drained and their native birds have been replaced by the introduced generalists. We still have banded rail; spotless crake is probably, and marsh crake possibly, still present. Bitterns turn up occasionally, but seem to be nesting no longer. Brown teal are hanging on due to intensive management at Okiwi, but grey duck may have been totally replaced by mallard.

The Great Barrier Island Charitable Trust proposed a monitoring plan, and has received funding for it from the Dept. of Conservation (Advice Fund) to produce an annotated checklist. We’ll carry out counts of selected species over one weekend every three months. This will require a team of observers, scattered at key locations across the island and co-ordinating their counts. If you’d like to be involved or want to get more information contact John Ogden (09 4290 980) Email: j.ogden@auckland.ac.nz) or the Trust secretary Fenella Christian (Fenella@xtra.co.nz). You don’t need to be a whiz ornithologist to do this. If you have a pair of binoculars it will certainly help, but counting sparrows, kingfisher nest holes in roadside banks or moreporks calling at night, is not rocket science. The main requisite is enthusiasm!