Fanged pitcher plants and other shelters

Our captive Hardwicke’s woolly bats (Kerivoula hardwickii) preferred pitchers of bat-adapted Nepenthes hemsleyana  plants (see previous blogs), and all woolly bats radio-tracked by Michael and Caroline Schöner in their primary study area consistently returned to the preferred N. hemsleyana pitchers. However the Schöners also found woolly bats in other kinds of plants. Even in their study area they occasionally found an apparently desperate bat roosting in fanged pitcher plants (Nepenthes bicalcarata). This amazing plant relies on a pair of sharp, fang-like, nectar-producing structures above its entrance to facilitate capture of ants that climb down to reach nectar. Approaching ants lose their footing near the tips of the narrowing “fangs,” falling into the water-filled pitchers. Bats can use these pitchers only if they are first drained.  This requires a drain hole near the base. No one yet knows whether these holes are made by inventive woolly bats short on alternative shelter or by birds or other animals, perhaps seeking a meal of captured insects.

At other locations, where the bat-adapted N. hemsleyana plants are not available, the Schöners also found woolly bats roosting in yet a third kind of pitcher plant (Nepenthes ampullaria), as well as in the unfurling leaves of wild ginger plants (Alpinia sp?). This raises an interesting question. Are similar bats, using different kinds of roosts actually cryptic, but distinct species yet to be discovered? Genetic analyses currently being carried out by the Schöners may reveal fascinating surprises.

Pitchers of N. ampullaria are clearly not well adapted for bats. Like those of  N. bicalcarata, they must be  punctured and drained of water before bats can even consider attempting to roost in them. Also, they do not provide a protective lid or operculum that would help shield bats from rain or predator detection. This plant has largely moved away from carnivory and now acquires much of its nutrients from capturing leaf litter that falls to the forest floor, though it still provides a spiny-looking “ladder” to help climbing insects enter. Unlike N. bicalcarata, it rarely has nectar glands for attracting  them. By comparison with these two species, N. hemsleyana pitchers, which now rely on nitrogen from bat droppings, are seven times less efficient than related species at trapping insects and seldom obtain energy from falling leaf litter.

Following a shaky beginning, our trip did have a wonderful ending. In addition to documenting the Schöners’ classic research, and the unique behavior of their woolly bats, local biology professor Dr. Ulmar Grafe organized a lecture in which Merlin was able to inspire members of the Brunei Nature Society at the Universiti of Brunei Darussalam with a much greater appreciation of bats and their conservation needs.  And on departure, we were able to supply Dr. Grafe and the Schöners with complete documentation of pitcher plant research, as well as 51 photos illustrating Brunei bat diversity and values, now to be used in producing educational materials. A week after our 34-hour-long return trip, we are still finding it difficult to adjust to an 11-hour time change, but are most grateful to our hosts, Michael, Caroline and Ulmar for making this trip such a success.