Conservation Week bat chat draws keen crowd
Dr Brian Lloyd points to the location (red dots) of bats detected in Golden Bay. Historical bat sightings are marked by blue dots.
Some 50 people turned up during Conservation Week at the Community Centre to hear native bat researcher Dr Brian Lloyd.
Dr Lloyd spoke and presented his work on a five-year-long bat conservation programme that aims to evaluate the state of the species in the top of the South Island and raise awareness of our only endemic terrestrial mammals, which few New Zealanders know much about. Of particular interest to his Golden Bay audience was his identification of a remnant population of long-tailed bats up the Aorere Valley, and the strong likelihood of other colonies in eastern Golden Bay.
Said Dr Lloyd: “Our image of pre-human New Zealand is that it was islands inhabited by millions of birds, but it’s just as likely at night that our primeval forests were full of flying bats. These probably started disappearing with the arrival of the kiore or Polynesian rat, which came with the first Maori migrations. Then we had the introduction of ship rats and stoats. Slowly these predators have chipped away at the populations until we have what’s left today.”
One species, the greater short-tailed bat (Mystacina robusta), survived right up until the 1960s as small remnant populations spread over Big South Cape Island and Solomon Island, off the bottom of Stewart Island. It was thought that a plague of ship rats arrived and eradicated them around 1967, however a recent sighting of bats flying on a nearby rock stack suggests this may now not be so.
For any practical purposes though, New Zealand now has only two species left. The long-tailed bat (Chalinolobus tuberculatus) is active both at dusk and into the night, while the lesser short-tailed bat (Mystacina tuberculata) is more nocturnal, not venturing out to fly until well after dusk, which is why these ones are less seen. Both species have bodies about the length of a person’s thumb, around five to six centimetres from nose to tail, with membrane wings stretching out to 30cm. Dr Lloyd said of handling short-tailed bats that they have the sharpest of teeth and attack like a “little rottweiler”. The Maori, he said, called all bats pekapeka, and left them quite alone.
Bats are the only mammals capable of sustained flight, thanks to translucent wing membranes supported by extended finger bones. Both New Zealand species are skilled flyers, achieving speeds of 60km per hour.
Like most bat species, our two bats rely on echolocation for foraging and navigation. They emit rapid pulses of high-frequency sounds and interpret the echoes from these sounds to “visualise” their surrounding environment. Explained Dr Lloyd, “Most of the sounds they make are well above the level of human hearing, lucky for us, because if we could hear them, it would probably sound as loud as standing next to a revved-up 747.”
The point was made many times in the evening just how social these animals are. Short-tailed bats live in tight colonies of up to 4,000 to 5,000, although populations of 10,000 are not unknown. In most other countries bats are often found living in caves, but ours prefer to roost in tree cavities, filling hollow cores or holes which they then excavate further with their sharp teeth. They shift roosts endlessly, whole colonies just moving from one night to the next between their old “colonial” roost trees and newer tree cavities, which can be kilometres apart. They do fly into caves, but mostly just to socialise with each other, postulates Lloyd.
Mating occurs in late summer, but there is a biological delay in the pregnancy, which doesn’t activate until the spring. This means all the baby bats are born in early summer. Bats give birth to live young, a single, naked, blind pup a quarter the size of the mother, which they then proceed to suckle. The mother carries her baby from roost to roost, coming back to feed them several times in the night.
Dr Lloyd says that, because a bat can lift an object one-and-a-half times its own weight, it’s no trouble for the mothers to carry their babies. “One I saw was hanging down from its flying mother, attached by its mouth and swinging from her nipple.” By four or five weeks the pups are covered in fur, their eyes have opened and they can fly.
Bats live up to 30 years, comparatively long for such a small animal. During winter, bats hibernate, which entails periods of torpor lasting six to ten days, interspersed with bouts of activity that may last a few hours or a few days.
Dr Lloyd confirmed the presence of a long-tailed bat colony at the head of the Aorere last summer, but says there is also strong historical evidence to suggest bats still exist amongst the beech forests on the eastern side of Golden Bay, along the Abel Tasman, Wainui hinterland and Pikikiruna Range. He is sure there are also bat colonies existing in the St Arnaud area. “You really know when you come to an occupied short-tailed bat roost tree in the beech forest, especially in the afternoon from about 4pm when they wake up and get ready to leave for the night. It’s like the tree is singing; their combined squeaking can be heard from at least 20 metres away. Also there can be a pile of guano two metres high up the tree trunk.”
Dr Lloyd says the bat’s future is not all that bright, especially as there is no long-term plan to help them. “We don’t know numbers for sure, but we can likely say their populations are still subject to a gradual whittling away. Everything from beech forest logging to rat and stoat predators have taken their toll.”
The possible effect of 1080 and rat poisons on bats is unknown, said Dr Lloyd, “but there is some evidence to suggest we should be concerned about the effect pest control operations is having on short-tailed bat populations because the species feeds on the ground. However, it is very unlikely that the poisons affect long-tailed bat populations because the species only feeds on flying insects.”
All in all though, Golden Bay people can rightly be proud of the fact they have some bats in their backyard. Dr Lloyd’s visit was arranged by NZ Forest & Bird’s Golden Bay branch.
Gerard Hindmarsh
