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The shearwater and tuatara share a home

Posted in Animals, Birds, Nature, Wildlife on Thursday, 28 February 2013

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This edited article about animals originally appeared in Look and Learn issue number 165 published on 13 March 1965.

tuatara, picture, image, illustration

Tuatara

Nature often arranges odd partnerships between different creatures which can be of use to each other. For years one such alliance was believed to exist in the waterless offshore islands of New Zealand, where the tuataras, lizard-like creatures, were popularly supposed to make use of the burrows dug by colonies of sooty shearwaters, which are members of the petrel family of sea-birds.

Such an arrangement could work quite well, for the swift-flying sooty shearwaters only use their burrows for nesting or occasionally for resting in at night, while the tuataras are nocturnal creatures which retire underground during the day.

When the tuataras want to hibernate for the winter the shearwaters have already winged their way northwards. Consequently the two creatures would rarely need to occupy a burrow at the same time.

Unfortunately for this theory, the latest observations do not bear it out. Not only are the islands in question riddled with burrows, so that it is impossible to say whether they were dug by the sea-birds or the lizards, but the tuatara is known to eat the shearwater’s young. Not the act of a friendly lodger!

What are these creatures like that inhabit these lonely islands, and why could they have been believed to have worked a “lodger” system?

The slow-moving tuatara (sphenodon punctatus, from the rhynchocephalia group) is one of the most primitive reptiles left. Sometimes described as a “living fossil,” it is the sole survivor of the beak-head reptiles which flourished millions of years ago, before the age of the dinosaurs.

Fossils of this reptile have been found in South Africa, South America, Eurasia and even Britain, but the actual tuatara has survived only in the remote islands of New Zealand where, because of lack of water, there are no creatures like weasels, rats or wild cats to hunt it down. It is such a valuable specimen that it is protected by government law from slaughter.

Olive-brown and yellow spotted, with a crest of yellow scales down its neck and back, the tuatara has a remarkable “third eye” in the top of its head. In young reptiles, a transparent scale covers this opening in the roof of the skull, with a “lens” but no iris. As the reptiles grow older, the skin thickens over this big brown “eye” until it is doubtful whether any light enters at all.

The tuatara was said to keep the burrow free of pests while the owning shearwater bird was away. This should have been easy, for the tuatara lives on a diet of insects, worms, snails and the wingless grasshoppers native to New Zealand.

Many burrows are dug by the shearwater bird, which uses its hooked beak to delve deep into the thick compost of leaves, twigs, shells, feathers and dead insects which litter the ground under the canopy of trees on the islands. As the shearwaters live in colonies the islands are riddled with burrows beneath the topsoil, sometimes three to a square yard.

The shearwaters (also called the mutton-bird) belong to the petrel family (procellardiidae) of web-footed sea-birds. Magnificent in flight, they can glide on their black, pointed wings, for nearly a mile above the surface of the ocean, dipping down to catch fish or plankton. The distances they cover are fantastic, over thousands of miles to Greenland and the Faroe Islands each winter in search of warmer ground and back each spring (September) to breed on the New Zealand islands.

One of the strangest things about the sooty shearwaters is that when they set off for their wintering grounds in the Northern Hemisphere, they leave their young behind. Somehow the young birds manage to find their own way over the vast seas to join the parent birds – by what instinct no one has yet discovered. . . .

Meanwhile, as the fledgling shearwaters swoop off northwards across the oceans the tuataras settle themselves peacefully into their own burrows for the winter. . . .

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