The greater short-tailed bat has an extremely broad ecological niche, and appears to represent the closest that bats have ever come to re-evolving flightlessness in the absence of any native mammalian predators or competitors – a condition also common amongst many of New Zealand's bird species such as kiwi and moa. However, the greater short-tailed bat also shared the fate of many flightless New Zealand birds following the introduction of exotic mammals to this remote landmass.
Previous distribution
Subfossil remains indicate that greater short-tailed bats formerly occurred across both the North and South Islands of New Zealand before Polynesian arrival in the region c. 700 years ago, as far north as Northland. However, by the twentieth century, relict populations of greater short-tailed bats apparently only survived on two islands off Stewart Island at the southern tip of New Zealand, Big South Cape Island (Taukihepa Island) and the tiny neighbouring Solomon Island. Big South Cape Island was also the last refuge of relict populations of three New Zealand endemic birds, the South Island saddleback (Philesturnus carunculatus), the bush wren (Xenicus longipes), and the Stewart Island snipe (Coenocorypha iredalei).
Evolutionary Distinctiveness
Order: Chiroptera
Family: Mystacinidae
New Zealand is the most remote large landmass in the world, having separated from the prehistoric southern supercontinent of Gondwana over 80 million years ago. Although primitive mammal fossils are now known from the mid-Miocene of New Zealand, the only native mammals in its modern terrestrial fauna are two species of otariid seals and three species of bats: the greater and lesser short-tailed bats and the long-tailed bat. Its terrestrial ecosystems are instead dominated by birds, many of which have evolved into flightless, large-bodied species that can be strikingly convergent with mammals (e.g. kiwis).
The long-tailed bat (Chalinolobus tuberculatus) is a member of the Vespertilionidae, a globally widespread family. It is a relatively recent colonist of New Zealand, and the genus Chalinolobus contains 14 other species found in Australia, New Caledonia, and several other Pacific islands. Conversely, the greater and lesser short-tailed bats are the only modern members of the Mystacinidae. Fossil mystacinids have now been recorded from the Miocene of Riversleigh, Australia, but today this bat family only occurs in New Zealand. This biogeographic distribution is similar to that of other ancient Gondwanan groups such as southern beeches, leiopelmatid frogs, tuatara, acanthisittid wrens, and the giant extinct moa, which are restricted to New Zealand or other fragments of the ancient southern supercontinent of Gondwana.
Mystacina robusta was formerly considered to be a subspecies of M. tuberculata, and was only widely recognised to be a distinct species after it had become extinct.
Description, Ecology and Habitat
M. robusta had a head-body length of 61-66 mm and weighed between 25 and 35 g. It was otherwise very similar to the surviving, slightly smaller lesser short-tailed bat Mystacina tuberculata ( one of the Top 100 EDGE species ). The thick coat was greyish-brown with paler underparts. The wings could be rolled up beneath a leathery membrane on the side of the body when the bat was not flying, allowing the forearm to be used as a normal forelimb for walking and climbing. Sharp claws, short thick legs, and grooves on the soles of the feet all further allowed the bats to run freely and be remarkably agile on the ground.
This species was found in forests and roosted in hollow trees (probably southern beech, kauri, totara, rimu, rata and kamahi), caves, crevices and seabird burrows. This species may have formed colonies of about 500 individuals or roosted in small groups. It has been suggested that births occurred from spring to autumn and a single offspring was produced in a litter. The diet was surprisingly broad, comprising fruit, nectar, pollen, arthropods, and also fat plucked from muttonbirds (juvenile shearwaters) and scraps of meat left to dry by hunters. They appear to have been convergent to some degree on small rodents, in the absence of similar species in New Zealand's pre-human fauna. Aerial prey was located by echolocation, but short-tailed bats are also well adapted for locating prey on the ground using their acute hearing and possibly also olfaction.
Size variation shown by subfossil material of the greater short-tailed bat shows a clinal pattern, with size decreasing significantly southwards across the North and South Islands. This is believed to represent a trade-off between selection for relatively large body size, to exploit the abundant macro-invertebrates and microvertebrates available on the forest floor, and the increasing cold-limitation of body size towards the south, where more energy was required to rewarm the bats from the near-ambient temperatures reached during torpor.
Factors leading to extinction
Greater short-tailed bats were apparently wiped out from the North and South Island mainlands by introduced rats, either the Pacific rat (Rattus exulans) introduced by the first Maori colonists, or black rats (Rattus rattus) and Norway rats (Rattus norvegicus) introduced by European colonists in the late eighteenth century. These rats impacted native bat populations either through predation, competition for food, and/or continual disturbance of roosting sites. These three rat species are also responsible for the extinctions of a large number of other New Zealand endemic species, such as flightless wrens and other ground-nesting birds, lizards and leiopelmatid frogs. Extensive deforestation across much of New Zealand during prehistory and recent history also removed large trees which would have formed important roost sites for this species.
Rats were accidentally introduced to the greater short-tailed bat's last refuge, Big South Cape Island, from a fishing vessel in 1964, but at the time many senior New Zealand scientists refused to believe that introduced mammals could be responsible for eradicating native species in island systems. This scientific resistance led national conservation planners to refuse the translocation of any of the island's threatened native species to other predator-free offshore islands, preventing practical conservation efforts to save these species for several years. By the time a rescue operation was finally permitted, it only proved possible to translocate South Island saddlebacks successfully on the first attempt; the greater short-tailed bat, bush wren and Stewart Island snipe all became extinct before further conservation work was carried out. Greater short-tailed bats were last observed on Big South Cape Island in 1967, and became extinct shortly afterwards.
www.edgeofexistence.org/extinctions/greater_shorttailed_bat.asp
