Bats and bat flies

Forest and Bird, Issue 265, 1 August 1992, Page 25

Bats and bat flies

Tim Higham

N 1973 when Kopi, the legendary giant kauri of Omahuta Kauri Sanctuary, toppled over a remarkable discovery was made. Lesser short-tailed bats killed during the tree’s collapse were found to have unknown spidery-looking flies crawling through their fur. The mouthparts of the flies, rather than being modified for piercing skin, were suited to eating guano and their claws were adapted for moving over fur. Subsequent work by the DSIR’s Beverley Holloway saw the flies described as the sole representative of a new family, Mystacinobiidae, a distant relative of the vinegar flies, Drosophila. Assisted by the fall of a second bat roosting tree in 1975, Holloway found the bat flies were totally dependent on the short-tailed bats for their survival. Wingless and blind, they fed entirely on yeasty droppings and required the constant 30° C incubator-like conditions of the bat colony. Female bat flies lay two batches of eggs in the guano-coated walls of the colony and die shortly afterwards.

Males act as a guard caste producing high-pitched sound through vibrating membranes near where their wings should be. The noise prevents the bats from interfering with the community or from eating the flies during grooming. When bats change roosting sites a

new colony of bat flies is started by those adults clinging to the fur of departing bats. Those that remain die with the cooling of the colony and depletion of the food supply. The greater short-tailed bat is thought to have had its own bat fly which became extinct with its host.

He says the lesser short-tailed bat is currently classified as vulnerable, but with rodents, feral cats and stoats present in its North Island localities he believes it will soon be endangered. Cyanide and 1080 poison baits for possums may constitute an additional threat. The north-west Nelson population, the only known South Island population, is already endangered, he says. Only

Codfish Island and Little Barrier Island appear to have healthy populations, despite the presence of kiore. Even the relatively common longtailed bat has declined markedly in European times through forest clearance and predation. Last century roosts were reported to contain hundreds and even thousands of bats. Few large roosts have been reported in the last 30 years and the majority contain between one and 50 animals, and average only about ten. Daniel says bats pose unusual conservation management problems, and methods which have proved successful for birds are probably not applicable to bats. In the vast North Island forest tracts the most immediate problem would

involve location of roost sites. On 1,359hectare Codfish Island many of the 15 large, periodically-used roosts were found only after considerable effort. Bats are very susceptible to roost disturbance and if transferred to island refuges would probably try to fly back. Even if roosts could be located the only currently available option is protection of that site from predators and from disturbance by humans. The only hopeful sign Daniel offers is that the lesser short-tailed bat has to date shown a propensity for "hanging on"’. Meanwhile regional DoC offices want to hear from the public about bat sightings, particularly in the lesser shorttailed bat areas of Northland kauri forests,

the volcanic plateau and East Cape, Tararua Forest Park and North-West Nelson Forest Park. All bats are totally protected by law and if found dead should be sent to the nearest DoC office with information about where and when they were found. A lot more work and some lateral thinking may be required before the draft recovery plan, about to be circulated among conservation managers and scientists, reaches its final form.

is a journalist

specialising in natural history. He currently works for DoC in Southland.