Bats and woodrose

Forest and Bird, Issue 265, 1 August 1992, Page 26

Bats and woodrose

OREST Research Institute scientist Chris Ecroyd has recently made an important ecological discovery. He has been able to confirm that the parasitic woodrose, Dactylanthus tayloni, is pollinated by lesser short-tailed bats. Ecroyd says he had long suspected the flowers of this rare plant were adapted to bat pollination. Their dull colour, strong scent and large quantities of nectar were characteristics consistent with bat-pollinated flowers described in overseas literature. He also knew that Mike Daniel had reported traces of Dactylanthus pollen in bat droppings from Omahuta kauri forest. He also thought that the terrestrial behaviour of short-tailed bats enabled them to pollinate flowers on the forest floor. Proving this theory, however, wasn’t easy. He first studied the timing of nectar flows and flower opening to see whether they correlated with the night-time activity of bats. There was no difference in the characteristics of the flowers between night and day. Next Ecroyd went to Little Barrier Island where Dactylanthus and lesser short-tailed bats were still known to co-exist. He borrowed and set up sophisticated night-vision video camera gear funded by the Lottery Board for kokako research. Instead of recording bats visiting Dactylanthus flowers, the video tape revealed kiore or Polynesian rats destroying them. In April this year Ecroyd had all but given up on proving his theory and turned his attention to filming the effect of possums and ship rats on Dactylanthus. He set up the

video gear in Pureora Forest, west of Lake Taupo, where there had been no confirmed sightings of short-tailed bats. When Ecroyd took the recorded tape home to watch during a lunch break it began much as expected, with ship rats visiting the flowers.

Half an hour into the tape he nearly dropped his lunch. A short-tailed bat appeared, the first of 40 visits in a night. While thrilled with the discovery, Ecroyd’s first reaction was a rational one — to remove the recording tab from the tape. By analysing the tape Ecroyd found all the visits were probably by the same bat, identifiable by tiny markings. Dactylanthus plants, he believes,

could play an important role in shaping the territories of individual bats and their foraging habits. In the North Island, Dactylanthus and short-tailed bat distributions are very closely correlated. In the South Island, outside the known range of Dactylanthus today, fossil records overlap. He believes Dactylanthus flowers evolved over millions of years in New Zealand’s forests to become dependent on short-tailed bats for pollination. Today ship rats may carry out the pollination, but they are destructive in the process. The biggest threat to Dactylanthus is possums, but Ecroyd’s discovery means at least some plants can be protected by wire netting with the mesh size large enough to allow the passage of bats. He says Dactylanthus nectar is likely to have been an important food source for short-tailed bats in the North Island, particularly over autumn, and the increasing scarcity of the plant may be a contributing factor in the decline of the bats. Short-tailed bats are likely to have been present in New Zealand in much higher numbers than even Maori realised, because of their nighttime activity which is confined to thick forest. They were also likely to have played a much more important part in forest ecology than is currently realised. Kiekie, Collospermum, nikau, rewarewa, rata and pohututkawa are other plants Ecroyd believes are pollinated at times by bats. In the forest ecosystem, bats probably fulfilled the roles of insect predators, prey for moreporks, hosts for flies and pollinators of plants.