Notes from New Zealand by Edward Kanze

Author:Edward Kanze [Edward Kanze]
Language: eng
Format: epub
Tags: Nature/Animals
ISBN: 9781640191501
Publisher: New Word City, Inc.
Published: 2018-04-02T16:00:00+00:00

Tuatara eat mostly invertebrate animals, such as cricket-like wetas and sow bugs; they also occasionally devour other tuatara and seabirds. For the island to support so many tuatara, it must hold an unusually large population of prey animals. According to ecological principle, a massive source of sustenance - plants, ultimately - must also be present to feed the tuatara’s food. And the plants themselves must have nourishment.

The driving force of the Stephens Island ecosystem is guano. Petrels and shearwaters defecate here in spectacular quantity. Their guano nourishes vegetation; the plants nourish small animals; the small animals nourish larger animals. At the top of the food chain, Old Beakhead sits like a king, awaiting the next insect, earthworm, seabird chick, or young tuatara to pass before his toothy mouth.

Tuatara inhabit Stephens Island in great number also because, as reptiles, they require a modest amount of food. Energy requirements are far lower for a tuatara than for a warm-blooded animal of comparable size; the tuatara wastes no calories in generating body heat. Tuatara live fairly passive lives (further conserving energy) and thrive at lower temperatures than any other reptile.

A staple food of the Stephens Island tuatara is a wingless cousin of the grasshopper called the giant weta. The giant weta is an endangered species (actually there are several species, but just how many remains to be resolved); it was common on the mainland until introduced predators eliminated it. Now its range is mostly limited to predator-free islands. A tuatara eating a weta is an irony - one endangered species feeding upon another.

Among New Zealand’s coastal islands, dozens are home to colonies of seabirds and invertebrates, yet none possesses a density of tuatara to match Stephens’s. Something is clearly special about Stephens Island, but the nature of that specialty has long remained a mystery.

At last, someone - Mike Thompson - seems close to a solution. By collecting tuatara eggs and incubating them under a variety of conditions at the university, he has demonstrated that they will not hatch if kept at temperatures below twenty degrees Celsius (about sixty-eight degrees Fahrenheit). Astonishingly, probes buried in soil in the Keeper’s Bush on Stephens Island have shown that the ground temperature there never reaches the twenty-degree Celsius threshold; the soil, shaded throughout the day, is always cool. Mike suspects that tuatara eggs buried under trees cannot develop because the soil is never warm enough to incubate them. Tuatara eggs planted in sunny paddocks, if left undisturbed, always seem to flourish.

This finding must be unsettling to the Wildlife Service, which has devoted considerable funds and manpower to re-vegetating Stephens Island with bush. If Mike’s preliminary findings prove correct, tuatara are flourishing on the island largely because of the sheep, not in spite of them, as had been long assumed. This theory could explain why bush-covered islands have fewer tuatara. On those lands, the reptiles may nest successfully only on treeless, north-facing cliffs. (In the Southern Hemisphere, slopes oriented toward the north receive direct sun.)

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