Long-tailed bats/Pekapeka

Long-tailed bat/pekapeka

Long-tailed bats at Karori Sanctuary

The long-tailed bat/pekapeka (Chalinolobus tuberculatus) was discovered in the Karori Wildlife Sanctuary in March 2004. While this is the bat most likely to be seen by the public, it is regarded as endangered in status. This discovery is exciting because it is the first time that bats have been confirmed in Wellington for many decades, probably a hundred years. We do not know how long they have been here, how far they roam to forage and where they roost. We are equally uncertain of how many there are and if  they are a new, increasing, population or a remnant, declining, one.

Bats in New Zealand

For millions of years, before people arrived in Aotearoa/New Zealand, bats or pekapeka were the only land mammals living here. Long-tailed bats arrived here about a million years ago, probably from Australia where their nearest relatives are found. As mammals, they are furry, warm blooded and feed milk to their young.

There are nearly 1000 bat species in the world but, in New Zealand, we have only two, the lesser short-tailed bat (Mystacina tuberculata) and the long-tailed bat (Chalinolobus tuberculatus). A third native species, the greater short-tailed bat (Mystacina robusta) is now extinct. In the North Island, most long-tailed bats are found in the Central North Island but there is a small population on Kapiti Island.

It is difficult to know how many still survive in New Zealand but estimates suggest several thousand nationwide. Because long-tailed bats have a large home range, are capable of travelling 25 km in a night to feed and usually roost in a different site every night, they are difficult to observe without specialised equipment, such as transmitters and detectors.

Feeding habits

Both surviving bat species are insectivorous (they feed on insects). The long-tailed bat hunts and catches its prey while flying. This is usually along the bush edge, above the canopy and along stream beds; places where insects are most common. They emerge from their roost sites at dusk and flit around, looking rather like butterflies. Short-tailed bats are unusual in that they often feed on insects on the ground. They are also important pollinators of some of our plants, such as Dactylanthus taylorii (a parasitic wood rose).

Echolocation

Insectivorous bats navigate and find their prey in the dark using echolocation. They make a series of short, very powerful, stabbing sounds—literally shouting repeatedly—whilst flying around and listening to the echoes bounced off objects in front of them. From this they build up a very sophisticated sound picture because the time lapse between sending the call and receiving the echo allows them to estimate distances. They can also interpret subtle differences in the echoes, which provide them with information about the size, shape and speed of the objects in front of them. As they home in on their insect prey or a perch, they send out more rapid signals to help them to manoeuvre precisely.

Different species produce different calls, but we cannot hear them because they are usually at ultrasonic frequencies beyond our hearing range. We can hear sounds below 20kHz, with our best hearing in the speech frequency range between 1 and 4 kHz, whilst bats can make sounds over a much greater range, between 10 and 200 kHz.  We have to use special equipment to detect the calls and then to convert them into sounds that we can hear.

• Listen to a recording of a long-tailed bat call, recorded at Karori Sanctuary in 2004 (15 seconds, wav format, 324 kB).

Recognition

Bats are usually seen at dusk. Long-tailed bats can be confused with swallows as they flit over water or along the bush edge. Each bat is about the size of a mouse but, at between 8 and 12 grams, about half the weight. Their wings make up 80% of their body surface area and have long fingers in them. This is why the scientific name for the bat is Chiroptera, which means hand-wing in Greek. Bats have more control than birds over their flight and are able to fly whilst carrying up to one and a half times their body weight! Because the long-tailed bat’s legs are connected to its tail and wings, it cannot walk.

Behaviour

Line-drawing of a bat

Female long-tailed bats congregate in spring and give birth to one baby which they rear in nursery colonies. They move the babies each night to a new location in the same way that the adults move each night to a new roost site. They usually roost inside large old trees, rarely in caves. Felling of the big trees, deforestation and the introduction of predators like rats, mean that bats are now nowhere near as widespread as in the past and, indeed, their numbers appear to be still in decline.

Long-tailed bats can live between 25 and 35 years, but large scale pest control in the parts of the country where they live will be important if they to continue to survive. Places like Karori Sanctuary can offer safe haven but, because they may only form part of their range the bats may well roost and give birth outside.

Between April and August, when it is cooler and insects are less active, the bats go into a form of hibernation, dropping their body temperature almost to the ambient temperature. They can rouse themselves on warm nights to go out and feed but are normally less active during the winter. As a result, most studies are undertaken during the spring and summer.