Bats are the only flying mammals. Their wings are delicate membranes stretched between the greatly lengthened bones of the hand. In some species a tail membrane between the legs provides an additional aid for flight. Except for these membranes, bats, like other mammals, are furred. They have sharp-pointed teeth and suckle their young. The ability to avoid obstacles by detecting echoes of high-pitched sounds is characteristic of the smaller bats. This faculty enables them to fly safely in dark caves, which frequently form daytime roosts, and it is also important for locating their insect food. Two species of bat occur in New Zealand. They are the only known native land mammals and are representatives of two distinct bat lineages. The Maoris called them “pekapeka” and they were the subject of an old native proverb predicting evil. They are named, respectively, the long-tailed and short-tailed bat.
(Chalinolobus tuberculatus (Forster))
This bat is a member of a genus with representatives in Australia, New Caledonia, and several other Pacific islands. The genus belongs to a cosmopolitan group of simple-nosed bats (Vespertilionidae), and New Zealand's long-tailed bat is probably a comparatively recent immigrant, for it is very similar to one Australian species. It is easily recognised, when caught, by the 1½ in. tail which is almost as long as the rest of the animal, and is included in a large tail-membrane which stretches between the legs (diagram 1). The ears are small and rounded, scarcely reaching above the fur of the head, and all the limb elements are long and slender. When fully extended the wings span 10–11 in., but at rest they are furled inconspicuously against the sides of the body. Fur colour varies greatly from black to reddish or chocolate brown.
(Mystacina tuberculata (Gray))
The short-tailed bat is unique amongst all bats and has consequently been placed as the sole representative of a special family, the Mystacinidae. It is probably the remnant of some ancient, more widespread, fauna and over long periods of isolation in New Zealand has undergone remarkable specialisations. These, being superimposed upon characters shared with the more primitive groups of bats, make family relationships difficult to interpret. It is recognised (diagram 2) by its long and rather pointed ears, by its prominent nostrils, and by its short stumpy tail which projects for about½ in. from the upper surface of the small, leathery, tail membrane. Its total length is usually between 2½ in. and 3 in.The remarkably robust limbs and large feet are also characteristic, and the double talons of the claws are a feature not known in any other bat. The wing span reaches from 10–12 in. and the fur colour may vary from light grey, through brown, to black. Individuals of the short-tailed bat from the Stewart Island region differ quite strikingly from North Island and northern South Island representatives. They are larger and more robust, with relatively short ears which do not reach beyond the nostrils as is the case in the northern form.
At rest a complicated wing-folding process occurs whereby the wing tips are enclosed in small pockets at the sides of the body, just forward of the thighs. The only exposed portions of the wings are thickened and leathery, thus protecting the more delicate regions from possible injury. Similarly, the delicate portion of the tail membrane can be tightly rolled against the body leaving only a thickened basal region exposed. This strange folding process is unique amongst bats. In combination with the robust limbs, large feet, and specialised claws, it permits the short-tailed bat especial freedom upon the ground or in trees. It is likely that this bat may obtain much of its food by hunting in such situations.
Very little is known about the ecology of New Zealand bats. Although reports of bats since 1930 include all provinces, as well as Little and Great Barrier Islands, Kapiti Island, Stewart Island, and several of its adjacent smaller islands, the species are nowhere abundant. In the North Island most records come from the Rotorua-Waikaremoana and Upper Wanganui River districts, while in the South Island the north-western corner appears to support the highest densities. Generally, bats are seen at forest margins, in cleared areas adjoining forest, or over rivers, lakes, swamps, etc., when these are near forest. The reduction in bat distribution during the last century has paralleled the extensive reduction of forested areas. Both species have failed to colonise urban areas. Most sightings of bats are made on fine, warm nights and, although only one or two individuals are usually seen, some flights of several dozen bats have been observed over water. The flight of both species is characterised by frequent changes of direction. Some records suggest that the short-tailed bat flies later than the long-tailed bat and that its flight is more direct than that of the latter species. The long-tailed bat emerges in the evening about half an hour after sunset. Sometimes short-tailed bats have been captured in dense forest after flying into lanterns or lighted huts. During the day both species may roost in hollow trees or caves. Sometimes individuals are found beneath the curled bark of trees, and there are occasional instances where bats have been disturbed amongst the folds of sacks in old sheds. Usually the number of bats found together is small, but colonies up to about 30 short-tailed bats and several hundred long-tailed bats have been observed. Whether such large colonies are formed only during certain months of the year for reproductive purposes, as is the practice with many bats in other countries, is a question that as yet remains unanswered.
by Peter David Dwyer, M.SC., Lecturer in Zoology, University of New England, Australia.