Bats

Bats are New Zealand’s only native land mammals.

In the short-tailed bat, the tail is only 12 mm (0.47 in) long, but extends for at least half of that length beyond the edge of the uropatagium (the membrane that extends between the thighs), whereas the longer tail of the other species is entirely enclosed within it and is clearly visible.

The Long-tailed bat – Chalinolobus tuberculata –  pekapeka-tou-roa.

Long-tailed bats are widely distributed throughout the mainland and on several offshore islands. They are probably in the Tangihua’s but have not been seen for a long time.

Long-tailed bats were common throughout New Zealand in the 1800s, but by 1900-1930 they were becoming scarce in many districts. They are now rare or extinct in most places.

Description

The long tailed bat is the more ‘common’ bat of the two,  usually found roosting in large, old canopy trees (e.g. rimu, puriri, totara, pukatea), either beneath the bark or in cavities. Bats can also find suitable roosts in mature exotic trees such as pine, gum and macrocarpa.

Characteristics of long tailed bats

• Long-tailed bats are smaller than the short-tailed bat, chestnut brown in colour, have small ears and weigh 8-11 grams.
• They are dark brown to black fur on torso, while the wings are virtually hairless
• They are believed to produce only one offspring each year.
• The bat’s echo-location calls include a relatively low frequency component which can be heard by some people.
• It can fly at 60 kilometres per hour and has a very large home range (100 km²).
• Long-tailed bats are capable of long distance flight – up to 50km in a single night, as they move between feeding and roosting sites.
• An aerial insectivore, it feeds on small moths, midges, mosquitoes and beetles.
• Preyed upon by the native ruru (morepork), feral cats, stoats, possums and rats.

Breeding

Females are generally more gregarious than males and forming crowded maternity roosts during the  gestation period. This  increases the bat’s temperature and consequently decreases the  gestation  period
Long-tailed bats mate in early autumn and a single offspring is born around mid-December. The young takes flight at five to six weeks old and females bear their first young around the age of two or three years.

Roosts

They have more than one roost which they frequently switch between (e.g. day and night roosts). Over winter the New Zealand long-tailed bat  hibernates, for up to four or five months in the colder parts of its range and for just a few weeks in warmer regions.

The lesser short-tailed bat  (Mystacina Tuberculata) Pekapeka-tou-poto

The endangered  lesser short-tailed bat is an ancient species unique to New Zealand and is found only at a few scattered sites. T hey inhabit forests from sea level to the  tree line  at about 1,100 m (3,600 ft)
Short tailed bats are divided into three subspecies:

• the kauri forest short-tailed bat – found only at two sites in Northland and one on Little Barrier Island
• the volcanic plateau short-tailed bat – known from Northland, the central North Island and Taranaki
• the southern short-tailed bat – found on Codfish Island and in the northwest Nelson and Fiordland areas.

In 2012 DOC listed the northern and southern subspecies as ‘nationally endangered’ and the central North Island subspecies as ‘declining’.

Description

Size 6 to 7 cm  long, with a wingspan of 28 to 30 cm. Adults weigh 10 to 22 g , although this may increase by as much as 30% after a full night’s foraging.

• Short-tailed bats are small, robust and stocky with prominent pointed ears.
• Short-tailed bats are found in native forests where they roost, singly or together in a group, in hollow trees such as kauri, rimu, totara, southern rata, kamahi and beech.
• The short tailed bat is thought to be a lek breeder, whereby. males compete for traditional ‘singing’ posts and `sing’ for a female.
• The short-tailed bat has also adapted to ground hunting and is one of the few bats in the world which spends large amounts of time on the forest floor, using its folded wings as `front limbs’ for scrambling around.
• They eat insects, fruit, nectar and pollen. Insects caught in the air or on the ground. Few other bat species eat plant matter.
• They usually fly quite low, around two to three metres above the ground.
• They scramble up tree trunks and along branches with remarkable agility and they burrow in and under leaf-litter on the forest floor to search for their food.
• They don’t do a true hibernation but go into a state of  ‘torpor’ in cold weather for a few days and stay in their roosts.

Foraging

short-tailed bats tend to forage on the forest floor making it an easy target for stoats and cats. They forage in areas of dense forest and deep leaf litter, and may travel considerable distances from roosting to foraging sites each night.

Diet

They eat insects, especially beetles, flies, and moths, as well as flowers, fruit, nectar, and pollen. The bats may be an important  pollinator  of the  wood rose  (Dactylanthus taylorii), a threatened  parasitic  plant which grows on the roots of trees on the forest floor.

Behaviour

Short-tailed bats are nocturnal, spending the day roosting in hollow trees. Many bats roost alone, using small cavities in the wood, but colonies of over a hundred individuals are not uncommon.
They have also been reported to chew out burrows within the wood using their sharp  incisor  teeth. Such burrows consist of hollowed out chambers connected by narrow tunnels up to several metres in length. They typically spend only a few weeks at any given roosting site, before moving on. Individual roosts may be reused repeatedly over the course of several decades.

The bats emerge from their roosts 20 to 150 minutes after sunset, and forage for much of the night. Short-tailed bats spend only around 30% of their foraging time catching insects in the air, typically flying less than 2 m above the ground,  and a further 40% feeding from plants. The remaining 30% is spent hunting on the forest floor,  a higher proportion than any other species of bat.
To assist with this unusual style of hunting, short-tailed bats are able to fold their wings inside a protective sheath formed from their membranes, and the wings have only a very limited  propatagium ( membranous structure that assists an animal in gliding or fligh) making them more flexible and mobile. Movement along the ground is also assisted by strong hind limbs and a robust  pelvic girdle, and by the additional talons on their claws.

They hunt their prey using scent, passive hearing, and echolocation. Their main calls have a wide bandwidth  and are multiharmonic, with a peak amplitude of 27 to 28 kHz. They also make shorter pulsed,  frequency modulated  calls.
The bats enter  torpor  in cold weather and stay in their roosts for up to 10 days at a time before emerging to feed. They may also enter daily torpor when roosting alone.

Reproduction

Short-tailed bats males occupy individual mating roosts during the breeding season and using repetitive ultrasonic calls to attract females. The males also mark the entrances to their mating roosts with an oily secretion produced in  scent glands  on the throat; the oil has a musky odour, and may help to attract the females. Mating most commonly takes place between February and May.

After mating, the embryo enters a state of  delayed implantation  through the winter, so a single young is born in the summer. Newborn bats are hairless, but otherwise well-developed, and weigh just 5 g. The permanent teeth erupt at three weeks, and the young are fully furred and able to fly by four weeks of age. They leave the maternal roost at six weeks, and grow rapidly; they are fully grown within three months.

Bat conservation

Threats

Causes of decline are combinations of:

• Clearance and logging of lowland forests
• Cutting of old-age trees for fire wood
• Predation by introduced animals such as cats, possums, rats, and stoats
• Exclusion of bats from roosts by introduced mammals, birds, wasps, and human interference.

New Zealand’s bats are rapidly heading towards extinction, often caused by rat plagues.

Saving our bats from extinction

Where you find bats, do not disturb them

– It is safe to watch bats as they emerge from roosts or feed, but sit quietly so they will not be frightened away. Some bats roost in limestone bluffs in late summer and winter, so rock climbers need to be careful not to disturb them.

Retain standing dead trees and old-age trees with cavities

– Dead trees and old trees with hollows and cavities are still valuable for wildlife. Bats rest by day and breed in cavities in old-aged trees. They move to a new roost tree regularly so are not always present at a site, but may return later to reuse it.
A social group can use over 100 different roosting trees. If woodlots are being felled, check trees for cavities first. Ask DOC for assistance in determining how they might be safeguarded.

Protect cabbage trees and other lone native trees on farmland

– Hollows in cabbage trees are also important roosts. Replant natives in these areas to shelter the trees and ensure their long term survival.

Protect old-age willow and poplar forest around ponds where bats feed

– Bats like to feed on aquatic insects over water. Ponds sheltered by overhanging trees help bats to feed in poor weather.