The history and present status of goats on the Auckland Islands (New Zealand subantarctic) in relation to vegetation changes induced by man

Abstract

Goats were liberated in at least 10 places on the Auckland Islands in the late nineteenth century as food for castaways. Only one population now survives, comprising about 100 animals. They live on the north-west side of Port Ross which is one of the driest and warmest parts of the main island.

The vegetation on parts of the island, but particularly where the goats now live, has been occasionally burnt and cleared. In summer 1972–73 the status of the goats and of their habitat was surveyed. A preliminary map was drawn of present vegetation around Port Ross, and permanent plots were established to follow continuing vegetational changes.

At sea level the southern boundary of goat distribution was a shallow stream. They were constrained altitudinally by the distribution of suitable food sources, and by weather conditions in the upland. Virtually the whole day was spent feeding, and reproductive behaviour, play, or inactive rest were not seen. Ninety-two percent of groups contained five or fewer animals who moved around meeting other groups and parting again. Because of the peat substrate, the goats had overgrown, split hooves and they ran poorly. Five goats caught by hand had body measurements that were, in general, above the means for a mainland population. Seventy-five percent were predominantly white or grey. Direct observation showed that open scrub and fine-grass swards were favoured above forest, tussock grassland, and dense scrub as feeding areas; a conclusion supported by the relative quantities of plant species in faecal pellets.

Palatable plants were potentially most abundant in the Myrsine divarlcata community which formed the scrub line. This community was too dense and too wet to be used by goats however, and in practice the best of the accessible sources were low-altitude open scrub, and fine-grass swards. Much of the forest interior was bare but this was due more to site history than to browsing by goats. In canopy gaps, forest plants regenerated within thickets of unpalatables, so that they eventually reached the canopy. In the same way, sites modified by man have regenerated, and this will probably continue even in the presence of goats.

The goats do not endanger plant communities or rare species within their present range, and are not likely to spread.