Tuatara: Volume 8, Issue 2, May 1960
New Zealand Bats
New Zealand Bats
Bats have a remarkably extensive distribution, even occurring on many remote oceanic islands. Flying foxes and blossom bats are found in tropical and subtropical zones from Africa to Australia and Polynesia. Some flying foxes measure five feet across the wings. These large bats comprise the suborder Megachiroptera, and with few exceptions have claws on both the thumb and index finger. The blossom bats have extremely long delicate tongues which they extend into flowers for nectar and pollen. They pollinate several tropical plants. Flying foxes congregate in roosting areas or ‘camps’ during the day and feed on fruit at night. Only the thumb is clawed in the small bats of the cosmopolitan suborder Microchiroptera. Generally insectivorous, this group includes also the true vampires, or blood-seeking bats, small tailless animals which, contrary to superstitious belief, are found only in tropical America.
Most bats of temperate zones hibernate during the winter months. They may be solitary, roosting beneath the bark of trees or at the sides of birds’ nests, or they may congregate in their hundreds or thousands in caves, hollow trees or disused buildings. Their hands modified to form large wings no longer serve for grasping, and most bats roost upside-down, clinging to rock walls or tree branches by the strong recurved claws of their toes. To many people bats are repugnant. Cold to touch and apparently stiff and moribund by day, these creatures take to the wing at dusk. Their remarkably silent flight is characteristic and it is little wonder that bats are held in superstitious fear. Even to the early Maoris the small ‘pekapeka’ foretold of death and disaster.
Two small bats, of the size of a mouse, are New Zealand's only known native land mammals. The few reports of the existence of a third species have not yet been confirmed. There are, however, instances of Australian bats being found here, but these are considered to be accidental wind-blown migrants. Both New Zealand bats are bush-dwelling animals usually seen only during twilight as they pursue insects over clearings or rivers and lakes. Fine summer and autumn evenings are favourable for observing these secretive animals.
Their rapid erratic flight makes observation on the wing difficult and identification to species virtually impossible. If captured, the species may be immediately distinguished by the length of the tail. In one, the long-tailed bat, the tail is almost as long as the head and the body, and is contained for its entire length in an interfemoral membrane stretched between the legs. The other bat has a short free tail above, but not page 62 reaching the hind edge of, the interfemoral membrane.
This short-tailed bat. Mystacina tuberculata Gray, is peculiar to New Zealand, and Dobson's suggestion that it was unique in being the most active climber of all bats appears to be substantiated by recent observations. Its agility is facilitated by the remarkable manner in which the wings may be folded. For this and other reasons its relationships are obscure and it is considered the sole representative of a family, Mystacinidae. In Chiroptera only the rare Myzopoda aurita of Madagascar shares comparable family status by itself. Some similarities are apparent between these two animals but at present our bat is considered most comparable with the widespread tropical group of free-tailed bats referred to as the family Molossidae.
Chalinolobus tuberculatus Forster, the long-tailed bat, is one of six species of the Australasian genus Chalinolobus. This group of lobe-lipped bats is most nearly related to South Africa's Glauconycteris and is included in the cosmopolitan family Vespertilionidae. The New Zealand Chalinolobus is closely similar to C. neocaledonicus of New Caledonia and C. picatus of northern and eastern Australia.
Knowledge of New Zealand bats dates from Cook's second voyage to this country during the late eighteenth century when Forster captured a long-tailed bat in Queen Charlotte Sound. Considerable confusion resulted from Dr. Gray's subsequent identification of short-tailed bats with Forster's animal. The New Zealand Chalinolobus was later synonymised with an Australian species, C. morio Gray. Past accounts of these animals are therefore difficult to correlate with the species as now known. This is particularly true of C. tuberculatus. Tomes' description, which alone is based with certainty upon New Zealand material, does not mention the characteristic lip-lobule and misses several other notable features. Because of these omissions from his description, the specific status of this New Zealand bat was not recognised. The structures themselves would have been indistinguishable in poorly preserved specimens.
Both species were formerly present over a greater part of New Zealand than now. Even at the beginning of the century they were still to be seen on occasion in some of the main urban areas. They were particularly recorded as roosting in large numbers under the bridges of the river Avon in Christchurch, but they have apparently failed to urbanise.
Of the islands adjacent to New Zealand, Little Barrier and Kapiti in the north and Stewart Island and its subsidiary islets in the south still support numbers of bats. Of these the southern islands have a considerable population of Mystacina but Chalinolobus has not been positively reported from them. The southern Mystacina are remarkably robust and differ in several other respects from their more delicate northern relations sufficiently to suggest a distinct subspecies. Data are as yet insufficient to determine the northern limit of this larger subspecies.
Our bats are nocturnal and generally insectivorous. Chalinolobus emerges in the early evening from late spring to autumn, and while occasionally seen on damp cloudy evenings it is more frequently reported on the fine warm nights of late summer and early autumn months. Flight is quick, soft and noiseless, and characterised by many rapid changes of direction. Group flighting is usual and regular feeding areas may be established; these changing only slightly from year to year. The numerous observations of C. tuberculatus over areas of water suggest that mayflies and mosquitoes form a substantial part of this bat's diet. The remains of these insects are found in bat droppings. Small moths and larger insects are sometimes taken and the rapid jaw action quickly reduces such items to a pulp.
Mystacina appears later, after dusk. On Stewart Island it has been found most active from 10 p.m. to midnight, but in the Rotorua district observations show that during the late summer it probably leaves its roost about 8 p.m. This two-hour interval would appear to correlate with the difference between the twilight times for the two areas. During summer this difference is of the order of two hours.
Mystacina pursues insects on the wing, flying at times close to the ground. It may come into the vicinity of lights and has sometimes stunned itself against torches and lanterns. In captivity Mystacina readily accepts food from the floor of the cage, and this together with its ability to run quite rapidly and its adeptness when climbing suggest that it may capture much of its food on the branches and leaves of trees. Food includes fairly large insects; spiders, crickets and moths being quickly accepted. Strong transverse ridges on the tongue of this bat are suitable for scraping flesh from animal carcasses and Mystacina has at times caused considerable damage to the bodies of mutton birds when these were hung to dry. It has not yet been determined whether this bat behaves as a natural scavenger.
Both New Zealand bats congregate in some numbers during the day although occasionally one or a pair of bats may be found beneath the bark of trees such as that of Kahikatea. The roosts occur in the hollow branches and trunks of large forest trees or in caves if these are near bush. A single roost may be inhabited for long periods and great accumulations of droppings are sometimes found. Such roosts are characterised by a strong musty smell.page 65
A roost of Mystacina usually contains seven to ten individuals of both sexes. A favoured hollow can be deserted for a week or more before being reoccupied. C. tuberculatus may form colonies of many hundreds but even such numbers as these are small in comparison with those of species elsewhere.
During the day the body temperature of bats drops. If disturbed at this time they are extremely sluggish and require a period of warming up before becoming active. This process involves yawning and stretching and disturbed bats may produce a shrill squeak. Of our bats only C. tuberculatus undergoes true hibernation.
The roosting habits permit ready transfer of ectoparasites between individuals and the fur of bats is usually infested. A relatively large bat flea is known from both our species. Mystacina is frequently host to numerous small mites.
Moreporks are the only native predators of bats and the wings of bats are sometimes found in their nests. Bats have been seen to escape an attack by flight in a fast upward spiral. Rats and the introduced mustelids are suspected in some localities of preying on at least Mystacina, and while records exist of capture by cats and dogs these latter animals would play but little part in reducing the numbers of our bats.
There has been a decrease in the distribution of native bats which is correlated with the restriction of forest. Over the hundred years for which we have information there does not seem to be any suggestion that the density of bats has decreased in unmodified forest. Food does not seem to be scarce. It has been suggested that increased predation is a major factor in limiting numbers but there is no good evidence supporting this view. Therefore it is suggested that the low numbers are not to be interpreted in terms of changes during the period of current knowledge, but rather as a result of long-standing factors. The possibility that low fertility or high mortality occur should be investigated, and accordingly studies of bat roosts are most desirable.
Skeletal Differences between New Zealand Bats
Skeletal material of bats is occasionally found in caves. This may be used for the identification of the two species. The very short (about 1.3 cm.) broad skull of C. tuberculatus is readily distinguished from the longer (about 2.0 cm.) and narrow skull of Mystacina. Immediate differences are apparent if the dentition is examined, for although C. tuberculatus has four upper incisors and six small lower incisors between the large canine teeth, Mystacina has only two relatively large upper incisors and a single pair of lower incisor teeth closely crowded between the canines. Two premolars and three molars are present in the upper and lower jaws of each bat but in Chalinolobus the first of the upper premolars is minute and easily overlooked.
A difference exists in the number of vertebrae present. Thus, while page 66 seven cervical, five lumbar, and eight caudal are present in each species, Chalinolobus has only eleven thoracic in contrast to the thirteen of Mystacina. The caudal vertebrae of Chalinolobus are greatly elongated, being half the length of the skull, while those of the short-tailed bat are much reduced.
In Mystacina the presence of three phalanges in the third digit and of accessory talons at the base of the claws provide a further distinction between the species.
The New Zealand Short-Tailed Bat
Mystacina tuberculata Gray (Figs. 1, 2)
Mystacina is represented in New Zealand by two distinct forms. One occurs throughout the North Island and is present in at least northern areas of the South Island, but the other is known only from Stewart Island and a few neighbouring islets. Skeletal differences other than those of size are not apparent between these two groups, but in their external appearance they are clearly distinct. In the absence of a full range of specimens the groups are here considered as subspecies.
The northern subspecies is a small delicately proportioned bat characterised by the length of the ears which reach to or beyond the tip of the muzzle, and by the remarkably prominent, though narrow, nostrils. Total length does not exceed three inches and the wing span is up to eleven inches. Gray's plate illustrates an animal which is clearly of this northern subspecies and this can therefore be provisionally recognised as M. t. tuberculata. In contrast the southern subspecies is larger and extremely robust with a total length of three or more inches and a span up to twelve. It has the ears falling short of the muzzle tip, and has the wide nostrils lying relatively close against the muzzle. Provisionally this subspecies may be recognised as M. t. robusta (Fig. 2). The following remarks may be considered to apply generally for any member of the species unless particular reference is made to the subspecies concerned.
LEGEND TO FIGURES
Fig. 1: Mystacina tuberculata, dorsal view. Fig. 2: (a) Head of M. t. tuberculata, ventral view; (b) head of M. t. robusta, ventral view. Fig. 3: Chalinolobus tuberculatus, dorsal view. Fig. 4: Head of C. tuberculatus, lateral view. Abbreviations: AB, antebrachial membrane; ATr, antitragus; BL, basal lobe of ear; C, calcar; E. ear; IF, interfemoral membrane; LL, lip lobule; PCL, post calcareal lobe: Ta, tail; Th. thumb; Tr, tragus.
Body colour varies from light grey, through brown to black, with the underside paler than above. The nostrils, ears and limbs are generally black but may be yellowish in grey forms of M. t. tuberculata. The membranes are usually dark brown or black. The hair comprises a close layer of short wavy underhair, with a sprinkling of longer, coarse overhairs or guard hairs. These guard hairs occur more densely in southern animals. All the hairs are tipped with white and unlike those of most other bats they do not show characteristic scale form. Their outlines are smooth and the scales are distinguished only with difficulty. Around the muzzle a number of stiff black hairs radiate in every direction. Short hairs occur on the ears, on the limbs and on the thickened portions of the membranes.
The crown of the head is raised only slightly above the level of the face, and the conical muzzle is long, obliquely truncated and terminated by the nostrils. The jaws are simple and relatively small, and the eyes are almost concealed by large fleshy lids. Extending well beyond the fur of the head are the simple ears, and arising from within each ear a long attenuate projection termed the tragus extends outwards from the side of the face.
Folds of the wing conceal the upper arm from above. The forearm provides a robust support for the membranes. The stout and somewhat hairy thumb carries a strong claw which bears a small subsidiary talon at its base. The long metacarpal bones of the palm radiate from the wrist and with the fingers of the hand support the wing membrane. The second digit comprises a single rudimentary phalangeal bone, the third has three phalangeal bones, and the fourth and fifth each have two. With the wing fully extended the third and longest digit reaches the full span, and the fifth reaches backwards from the wrist to provide the width of the membrane.
The membranes are remarkable for the thick and leathery appearance of those portions adjacent to the body. Strong cutaneous ridges passing from the sides of the body produce this texture. The ridges of the wing membrane pass over the upper surface of the thigh and are continuous with those of the basal portion of the interfemoral membrane. A reduced antebrachial membrane lies in the angle between the upper arm and the forearm and is similarly thickened. Elsewhere the membranes, while thin, are exceptionally tough and smooth contrasting with the delicate membranes seen in C. tuberculatus.
The thigh and lower leg are short and stout, but the foot is extremely large and the loose skin of the sole is deeply wrinkled. Basal talons are present on the claws of the foot as on the thumb. A weak calcar extends from the heel of each foot to support the posterior margin of the interfemoral membrane.
Only a short basal portion of the tail is included within the thickened part of the interfemoral membrane, and distally the tail extends from the membrane as a short projection curving above it. The membrane when page 69 fully extended is rounded posteriorly but it may be rolled forwards beneath the tail so that the distal half is entirely concealed by the thickened basal portion.
Adaptations for Climbing in Mystacina
In bats the forelimbs greatly exceed the hind-limbs in size. These latter generally play but little part in movement and are usually short and reduced. Most bats can only crawl or scramble on the ground. These animals usually furl the wing against the body when roosting, or at the most fold it in some simple manner. However, the Molossidae and the New Zealand Mystacinidae differ from other bats in that peculiar folding processes of the wing enable the forelimb to function fully in walking. These bats crawl of run quite actively by using their wrists.
Mystacina is remarkably agile and will run or climb even over smooth surfaces with complete freedom. The large and adhesive soles of the feet, and the basal talons at the base of the claws provide security when climbing. It is, however, the unique folding process of the wings in which the membranous portions are carried beneath the forearm and against the body, and the strange manner in which the interfemoral membrane may be folded beneath the tail, which facilitate the use of the limbs for walking, and make Mystacina the most ‘sure-footed’ of all bats.
When folded, the delicate portions of the wings are concealed beneath the forearm and within small cutaneous pouches at the sides of the body and along the thigh, so that they are protected from injury by the thick leathery portions which alone remain exposed. The folding process commences with the proximal phalanx of the third digit being turned inwards beneath the membrane. This carries with it the proximal phalanx of the fourth digit and the second (terminal) phalanx of the fifth digit. The short first phalanx of this fifth digit remains extended along the line of the metacarpal. The second phalanges of the third and fourth digits, and the distal region of the terminal phalanx of digit five turn backwards and lie close along the side of the body, between the thickened wing membrane and a cutaneous flap extending from the side of the body. This flap continues on to the thigh and conceals the terminal phalanx of the third digit which is directed outwards along this portion of the hind limb.
The interfemoral membrane is rolled forwards so that it lies close against the body at the root of the tail. Only the thickened basal portion remains exposed. With the wing and tail concealed in this manner the limbs are in no way impeded and can be used quite freely for walking.
The New Zealand Long-Tailed Bat
Chalinolobus tuberculatus Forster (Figs. 3, 4)
C. tuberculatus is a small delicately-proportioned animal characterised by the possession of a tail which is nearly as long as the body, and which for almost its entire length is included in a large interfemoral membrane continuous laterally with the membrane of the well-formed wings. When fully extended the wings may span from ten to eleven inches. The length page 70 from the tip of the snout to the root of the tail is about one and three-quarter inches and that of the tail one and a half inches.
Body fur varies in colour from black to reddish- or chocolate-brown, with the head and shoulders darkest, often black, and the underside paler. The pubic region may be yellowish brown. Limbs and digits are generally dark above and pale below, and the membranes appear brown or black. Fur is present over most of the head and body, is represented as bristles on much of the muzzle, and is somewhat sparse in the pubic region. It extends only slightly on to those portions of the membranes adjacent to the body and, with this exception, the limbs and membranes may be described as free of fur. The fine hairs measure up to 7 mm. in length, and under magnification show the peculiar scale structure so characteristic of bats. Unlike Mystacina there is no differentiation into overhair and underhair.
The head is short, broad and moderately hairy, with the terminal nostrils represented as low prominences. The jaws are well formed and may be opened to an angle of nearly ninety degrees; they are characterised by the possession of a small fleshy lip-lobule projecting laterally on each side near the angle of the mouth. The minute eye is almost covered by the well-formed fleshy lids. The ears stand slightly higher than the fur of the head, and lie behind the eyes. They have a small backwardly-directed lobe at the base of the inner margin. The ear tip is rounded and the outer margin of the ear is continued along the face, beneath the eye, as an antitragus which terminates just behind the lip lobule. The more pronounced tragus extends from within the ear above the antitragus. It is narrow at its base but widens above and is rounded distally.
The body is compact, tapering somewhat in front of the shoulders but not conspicuously behind. In both species of bat the short pendent penis in the male makes distinction between the sexes readily apparent.
The bones of the forelimb are, with the exception of those of the thumb, very long and slender. The small thumb projects freely from the wrist and carries a long curved claw. Bones of the palm and hand support the delicate wing membrane, but in contrast to Mystacina no bony phalanx is associated with the second metacarpal, and only two are represented in each of the remaining digits.
A well-developed antebrachial membrane extends between the anterior borders of the humerus and forearm. The extensive wing membrane proper extends from the sides of the body and from the full length of the legs except the toes. It is produced laterally to include the full extent of the fingers as shown in the figure.
In Mystacina the leg bones are short and stout, but in Chalinolobus they are long and slender, and the small foot is turned outwards. The calcar extends from the heel as a strong process, and lies along the posterior border of the large interfemoral membrane to provide support for almost half the length of this border. A small rounded post-calcareal lobe occurs near the base of the foot.
Relationships with Australian Bats
Six species of Chalinolobus are currently recognised and these fall neatly into four groups. C. tuberculatus, C. neocaledonicus from New Caledonia, and C. picatus from northern and eastern Australia and New Guinea form a single group readily distinguished from the three remaining species by the absence of fur on the wing membranes. In their colour pattern and in the form of their skulls members of this group are remarkably alike. Some doubt exists as to the validity of their specific standing.
In the remaining species body fur extends on to the underside of the wing membrane to a line passing from the elbow to the knee, and to a lesser extent it is also present on the upper surface. C. gouldi, the largest member of the genus, with head and body two and a half inches and tail two and a quarter inches, is represented in Australia generally, and occurs on Tasmania and Norfolk Island. It is distinguished by the presence at the mouth corner of a vertical skin tag which is an extension of the antitragus. The small C. rogersi is characterised by its hoary grey appearance, and by the absence from the upper tooth row of the minute first premolar found in other members of the genus.
C. morio, which at one time was confused with the New Zealand C. tuberculatus, is certainly more distinct from this animal than is any other member of the genus. It is a small chocolate brown bat occurring in Tasmania and south-eastern Australia, and differs markedly from others of the genus in the absence of the basal ear lobe, in the pointed ear tip and tragus, and in the larger postcalcareal lobe which is supported internally by a minute arm of the calcar.
I would like to express my appreciation to the Directors of the Dominion Museum and the Auckland Institute and Museum who have made study material available. The New Zealand Deer Stalkers' Association has actively co-operated in obtaining many recent records and observations from members throughout New Zealand. The New Zealand Speleological Society has located useful skeletal material and Miss P. Lewis has made available the details of four years’ regular observation. I am indebted to numerous other persons for their assistance in collecting data and to Professor L. R. Richardson for his supervision and instructive criticism throughout this study.
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GRAY, J. E., 1844 - Zool. ‘Erebus ‘and’ Terror’, No. IV, Pl. 22.
MYERS, J. G., 1921 - N.Z. Journ. Sci. Tech. 4: 139-141.
PARHAM, W. T., 1959 - Forest and Bird. No. 131, p. 8.
ROACH, R. W., and TURBOTT, E. G. 1953 - N.Z. Sci. Rev. 11 (11): 161.
STEAD. E. J., 1937 - Trans. Roy. Soc. N.Z. 66: 188.
TATE. G H. H. 1942 - Bull. Amer. Mus. Nat. Hist. 80 (7) pp. 221-297.
TOMES, R. F., 1857 - Proc. zool. Soc. Lond., part XXV, p. 134.