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Studies on the Two New Zealand Bats

II. Wing Folding and Terrestrialism in Mystacina tuberculata Gray (Chiroptera: Mystacinidae)

II. Wing Folding and Terrestrialism in Mystacina tuberculata Gray (Chiroptera: Mystacinidae)

Mystacina tuberculata Gray is one of the two bat species present in New Zealand, and is the sole representative of the family Mystacinidae. Some attention has been directed to a number of peculiarities in this bat which have been interpreted as adaptations suitable for terrestrialism. These conclusions were first indicated by Dobson (1876) who considered that the basal talons of the claws, the manner in which the wings could be protected from injury when .the bat was not flying and the structure of the foot were adaptations for climbing, and he suggested accordingly that "Mystacina hunts for its insect food, not only in the air, but also on the branches and leaves of trees, among which its peculiarities of structure most probably enable it to walk about with security and ease."

Dobson stated that in repose the first phalanx of the third digit is folded forwards upon the ventral surface of the metacarpel, the second phalanx is folded backwards on the first and the third forwards on the second. Hutton and Drummond (1904) and Miller (1907) claim that the first phalanx of the third digit is flexed upon the upper surface of the corresponding metacarpal when the wing is folded at rest. I find, however, that the manner in which the wing is folded differs considerably from the descriptions given by previous authors.

The following description is based upon a single female specimen of M. t. tuberculata in which the left wing was in the position of repose. The form of the metacarpophalangeal and the phalangeal joints would not permit the wing to fold otherwise. (Figs. A, B, C.)

In folding, the membranous portions of the wings are carried beneath the forearms and against the body and the uropatagium is rolled forwards beneath the tail. Ventrally the reduced propatagium extends beneath the stout forearm as a strong band which takes origin from the metacarpal region of the thumb. On each side this is produced beyond the posterior margin of the forearm so that a distinct concavity is formed between the band and the plagiopatagium. The delicate proximal portions of the wings are concealed within these concavities. The tips of the wings are contained within small lateral pouches present at the sides of the body, just forward of the thighs, and extending along the underside of the thighs. Only the thickened leathery portions of the wings remain exposed. Behind the wrist the ventral and medial aspects of the folded palm are protected externally by a thickened region of the membrane between the second and third metacarpals and by the fifth metacarpal together with a narrow, thickened ridge present immediately lateral to this metacarpal. This ridge extends onto the upper surface of the membrane for almost half the length of the metacarpal.

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 the fifth digit remains extended along the line of the metacarpal. The second phalanges of the third and fourth digits, and the flexible page 7distal region of the terminal phalanx of digit five turn backwards and lie close along the side of the body within the pouch formed between the thickened wing membrane and the cutaneous flap extending from the side of the body. This flap continues onto the thigh and conceals the terminal phalanx of the third digit which is directed outwards along this portion of the hind limb.

The distal portion of the uropatagium is rolled forwards beneath the tail so that it lies close against the body at the base of the tail. Only the thickened basal portion remains exposed. The calcar lies along the inner surface of the shank.


Mystacina is not, as far as can be ascertained, a crevice dweller, and the extreme protection of the delicate membranes from possible injury correlated with a maximum degree of freedom for the limbs must be interpreted in relation to terrestrial locomotion. Similar protection of wing membranes occurs in the molossid Cheiromeles torquatus with the wing tips being folded into pouches, but here the pouches are in the armpits and open backwards (Kitchener, 1954). In the molossids the ability to crawl rapidly is possibly an adaptation related to roosting. Eumops, for instance, is unable to take flight from a level surface (Vaughan, 1959). In Mystacina freedom of the limbs provided by the reduced propatagium and wing folding process, the robust limbs, the specialized claws, and the wide range of movement of the femur permitted by the form of the acetabulum are terrestrial or arboreal adaptations. The ability to take flight from level ground has been recorded for Mystacina and terrestrialism in this bat is not connected with roosting but is rather to be associated with foraging habits. The scanty information available pertaining to the ecology of this species does appear to substantiate Dobson's earlier conclusions.

M. t. tuberculata; Wing Folding

M. t. tuberculata; Wing Folding

Fig. A, Dorsal; Fig. B, Ventral; Fig. C, Diagram showing the relative positions of the metacarpals and phalanges of the folded wing, left ventral aspect.

Abbreviations: 3m, 4m, 5m, metacarpals of digits 3, 4 and 5; 3 ph. 1, 3 ph. 2, 3 ph. 3, phalanges of digit 3; 4 ph. 1, 4 ph. 2, phalanges of digit 4; 5 ph. 1, 5 ph. 2, phalanges of digit 5.