NZ wrens among the world’s living fossils
BOB BROCKIE
Rock wrens are one of New Zealand’s smallest birds, with no tails and such short wings they rarely fly more than 20 metres.
Few people see a rock wren because they live high up in the snowy Southern Alps. They used to live in the North Island but rats put an end to them there. These days, rock wrens are few and far between as stoats and mice are eating their way through their dwindling populations.
Rock wrens puzzled early bird watchers as they rarely saw these birds in winter, and they wondered where they went. It turned out that the watchers were standing on them, as the birds spent the winter living and feeding among the rock debris under the snow.
Until recently, New Zealand had two other kinds of wren – the bush wren and the Stephens Island wren. Bush wrens used to live in North and South Island forests, but rats and stoats wiped them out in 1972. No other animal has gone extinct in New Zealand since then.
It is often said that the lighthouse keeper’s cat caught and extinguished the only specimen of the Stephens Island wren in 1895, but that’s not the case. Birds were collected by the cat, by the lighthouse keeper and by professional collectors, who sold at least 16 of them to Walter Buller and Lord Rothschild for £5 each (about £500 pounds in today’s money).
These specimens have ended up in museums in London, Liverpool, New York, Philadelphia, Massachusetts, Otago and Te Papa.
These three wrens, and their cousin, New Zealand’s smallest bird, the rifleman, collectively belong to the same family that ornithologists call the acanthisittidae.
The amazing thing about these birds is that they are the most ancient of songbirds. DNA sleuths reckon that our wrens evolved about 80 million years ago and sit on the lowest branch of the songbird family tree. Although classified as songbirds, our wrens don’t actually sing. They squeak.
Our wrens originated in the southern continent of Gondwanaland, from which Australia and New Zealand broke away. In Australia the songbirds evolved into manikins, hornbills, swifts, swallows and many other kinds of bird.
From Australia they spread northwards to settle every country on Earth. All these birds would have looked down from their trees on dinosaurs pottering round beneath them, until 65 million years ago when that big asteroid hit the Earth.
The meteoric cataclysm wiped out the dinosaurs but, amazingly, all these songbirds, including our wrens, flew and sang their way through it. The molecular clock shows us that other songbirds, such as pigeons and cuckoos, tits, honeyeaters, thrushes, and crows, evolved after the cataclysm to become today’s nearly 6000 delightful species.
Because our wrens are among the world’s living fossils, and because stoats and mice are threatening their existence the Department of Conservation has gone to a lot of to trouble transfer more than 40 to Fiordland’s almost predator-free Secretary Island. They appear to be breeding successfully.