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Bats

by  Veronika Meduna

Few people will have seen New Zealand’s thumb-sized native bats – the country’s only native land mammals. In pre-human times, they darted about the forests in their millions, but today they are reduced to a few scattered groups. We are only now beginning to learn more about these tiny creatures of the night.


Bats in New Zealand

New Zealand has only two native land mammals, and they are both bats – the long-tailed bat (Chalinolobus tuberculatus) and the lesser short-tailed bat (Mystacina tuberculata). They have bodies the size of a person’s thumb (5–6 centimetres from nose to tail) and a wingspan of nearly 30 centimetres. The Māori name for both species is pekapeka.

Greater short-tailed bat

New Zealand was recently home to a third species, the greater short-tailed bat (Mystacina robusta). It disappeared from the main islands of New Zealand soon after the Polynesian rat arrived, about 750 years ago. From 1840 until the 1960s the greater short-tailed bat was confined to Big South Cape Island and Solomon Island, off the coast of Stewart Island. These rat-free islands were a refuge for birds, bats and insects that had disappeared from the main islands. However, the arrival of ship rats on Big South Cape and Solomon islands some time in the 1950s or early 1960s was devastating for animals and plants alike. Greater short-tailed bats have not been seen alive since 1967. The species is considered extinct.

Flight and echolocation

Bats are the only mammals capable of sustained flight, thanks to transparent wing membranes supported by extended finger bones. Both New Zealand species are skilled fliers. Lesser short-tailed bats have been timed at speeds of up to 60 kilometres per hour.

Like most bat species, New Zealand’s bats rely on echolocation for foraging and navigation. They emit rapid pulses of high-frequency sounds and detect the echoes from objects nearby. Most of the sounds they make are above the level of human hearing.

Time of activity

The lesser short-tails are nocturnal, flying well after dusk. Long-tailed bats are active both at dusk, and into the night.

Reproduction

Bats are mammals and give birth to live young. Mating occurs in late summer, but there is a delay before pregnancy begins in spring. After a pregnancy of six to eight weeks, New Zealand’s bats give birth around December or January to one naked, blind pup, about a quarter of the mother’s size.

Pups are born in a communal maternity roost, usually a large cavity in an old tree, and they are carried to a new nursery roost each night by their mothers. The mothers return to feed them several times during the night. By four or five weeks of age the pups are covered in fur, their eyes are open and they can fly. It is not known whether they continue to be fed by their mothers once they start flying.

Age

Bats are generally long-lived. The life-span of New Zealand bats has not been determined, but long-tailed bats that have been banded are known to live more than 11 years, and short-tailed bats at least seven years. It is possible that both species could live for 30 years.

Torpor and winter hibernation

Bats can enter a state of torpor where they become motionless and their body temperature drops to a level close to that of their surroundings. This strategy helps bats conserve energy in unfavourable conditions. Long periods of torpor extending into weeks or months are known as hibernation. During winter both New Zealand species hibernate. Winter hibernation is usually made up of periods of torpor lasting for 6–10 days, with bouts of activity that may last for a few hours or a few days.


Lesser short-tailed bats and long-tailed bats

New Zealand’s two native bat species are the lesser short-tailed bat and long-tailed bat.

Lesser short-tailed bats

Lesser short-tailed bats (Mystacina tuberculata) are stocky little animals with pale grey-brown fur, long pointed ears and a stumpy tail. They are the only surviving members of the Mystacinidae family of bats.

Scientists once considered short-tailed bats to be one of New Zealand’s ancient animal species. DNA evidence now suggests they are more recent arrivals. Species like the tuatara and peripatus have been present since the breakaway of New Zealand from Gondwana 85 million years ago. But Mystacinidae fossils occur in Australia, and it is likely that the ancestors of New Zealand’s short-tailed bats crossed the Tasman Sea from Australia between 16 and 28 million years ago.

Unique adaptations

Once they arrived in New Zealand, lesser short-tailed bats continued to evolve. They developed characteristics not found anywhere else in the world and have become a biological oddity. They are the only bat species that forages for food on the ground, like small rodents. Several adaptations make this possible: their robust hind legs have small claws, and their wings fold down completely and can be tucked away under side flaps of thicker skin. This allows the bat to use the elbow part of the wings as front legs.

Hitchhikers

Colonies of wingless batfly (Mystacinobia zelandica) live alongside short-tailed bats. Adult batflies and their maggots feed on bat guano (manure). When bats leave one roosting site for another there are usually a number of batflies clinging to their fur. By hitching a ride, the insects can set up colonies in new bat roosts.

Short-tailed bats are the only species of small bat which carry out lek mating (where males assemble in a special area and compete for the attention of females). During late summer, male short-tailed bats gather at strategic trees near communal roosts and attempt to attract females with prolonged singing bouts.

Feeding behaviour

Lesser short-tailed bats feed on almost anything, including insects, fruit, pollen, seeds and nectar. They often scurry around on the ground like small mice, fossicking under leaf litter in search of bugs. They rely on sound and smell to locate food on the ground, but use echolocation to catch flying prey. They do not usually fly until well after dusk, and typically stay within 10 metres of the ground.

Long-tailed bats

Long-tailed bats (Chalinolobus tuberculatus) are more delicate than the robust short-tailed bats. They have chocolate-brown fur, short ears, and a tail that is enclosed within a membrane stretched between their legs.

They belong to a genus of bats found commonly in Australia, Norfolk Island, New Guinea and New Caledonia. Ancestors of long-tailed bats were probably wind-blown across the Tasman Sea relatively recently (within the last 2 million years).

Although they are more common than short-tailed bats, long-tailed bats are seldom seen. They emerge from their roosts around dusk and fly off to hunt. They feed exclusively on flying insects.

Long-tailed bats form complex social groups. Research on radio-tagged bats in Fiordland’s Eglinton Valley has shown that the bats frequently switch between roosting alone and roosting with a colony, often staying only one night at the same place.


Habitat, distribution and conservation

Habitat

Both species of New Zealand bat are found in native forests from sea level to the treeline. Their natural habitat is mature forest with many large hollow trees. These trees are used as roosting sites by the bats, either singly or in colonies of up to 100 individuals. Long-tailed bats also roost in caves at times, and some colonies have become established in mature pine (Pinus radiata) forests.

Human impact

Lesser short-tailed bats and long-tailed bats were once numerous and widespread in forested regions. The most conservative estimate for the pre-human population of lesser short-tailed bats in the central North Island is 12.5 million.

Human settlement had a drastic effect on the number of bats. Causes for their decline include:

  • loss of habitats through clearance and logging of lowland forests
  • introduction of new predators
  • competition for roost sites from introduced mammals, birds and wasps
  • human interference and disturbance of roost sites.

Rats, stoats and cats are key predators, particularly during winter when roosting bats are immobilised by torpor for long periods. The short-tailed bat’s ground-feeding habit also makes it an easy target.

Distribution

By 2005, short-tailed bats were restricted to 13 populations:

  • two large ones on Little Barrier Island (in the Hauraki Gulf) and Whenua Hou/Codfish Island (off Stewart Island)
  • seven in the central North Island, with about 40,000 bats
  • four small, isolated populations (two in the North Island, two in the South Island).

Long-tailed bats are found in scattered populations, from the north of the North Island through to the western South Island and south to Halfmoon Bay on Stewart Island. They are also found on Great Barrier, Little Barrier and Kapiti islands. They survived in some cities until the 1920s and 1930s.

Conservation status

Although both species are under threat, the lesser short-tailed bat is ecologically more precious as it is the only remaining species within its family.

Conservation programmes

Department of Conservation (DOC) programmes focus on protecting roosting sites, enhancing habitats and controlling predators, as well as education. DOC has a recovery programme which aims to ensure the survival of bats, and to establish new populations within their historical range.

Pollinating plants

Lesser short-tailed bats are important pollinators for a number of indigenous forest plants, including kiekie, pōhutukawa, wood rose and perching lilies. While none of these plants depends solely on bats for pollination, bats are often more effective at it than birds. Lesser short-tailed bats also spread plant seed in their droppings.

Captive husbandry of bats is possible, and captive breeding is being attempted. Short-tailed bat pups bred in captivity were successfully moved to predator-free Kapiti Island in 2005.

Live bats are protected by the Wildlife Act 1953 and must not be disturbed. If any dead bats are found, their bodies should be sent to a major museum or the nearest DOC office, with information about where, when, and by whom they were collected.


External links and sources

More suggestions and sources


How to cite this page: Veronika Meduna, 'Bats', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/bats/print (accessed 20 November 2019)

Story by Veronika Meduna, published 24 Sep 2007