To catch a thief

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The subject didn’t know he was being filmed, but this wasn’t Candid Camera, and nobody was prattling on about what a rewarding job being an insurance rep had turned out to be. What we had on this occasion was a robber.

It was a dark night, and only an ultra-sensitive electronic eye could have detected the beam of infra­red light which was producing the black and white image on the security monitor.

The villain was instantly recognisable: a notorious Australian crim. His name has been mentioned in connection with various offences, including swal­lowing the embryos of endangered species—a real animal.

A brush-tailed possum, in fact, and this time he had put himself right in the frame. The security camera had caught him in the act of robbing a kokako nest, and consuming the pre­cious clutch of eggs it contained.

Conservation biologist John Innes, of Landcare Research in Rotorua, has spent the last two years studying kokako breeding in Rotoehu Forest. He’s long suspected that nest predators are contributing significantly to the decline of the species in the North Island, but information about which particular predators are involved has been hard to obtain. Catching a predator in the act of robbing a nest is not easy, especially since the nests are in trees, some­times 30 metres above the ground, and most of the attacks happen at night.

Last year, Innes started using security surveillance equipment to monitor some of his kokako nests. Elec­tronic surveillance causes a minimum of disturbance to wildlife, and new time-lapse videotape recorders developed for the security industry have made it unnecessary for scientists to get up in the middle of the night to change the tape.

The new recorders can be set to record at a much slower speed than the 24 frames a second used in a normal television picture. At one frame a second, for instance, a three-hour tape will run for 72 hours. When played back at normal speed, the effect is to speed everything up, and the villains caper about like characters from the silent film era. But they are still readily identifiable in a freeze-frame. During the kokako breeding season—from November to March­Innes managed to record two kokako nests at Rotoehu. The possum incident took place at one of these nests, but at the other, two kokako chicks  were successfully hatched.

During filming of the second nest, a ship rat visited the sitting female kokako on most nights, but her presence seemed to be enough to deter any serious attempt to attack the chicks. Whether this was a case of a particularly gutless rat matched against a braver­than-average kokako isn’t known, but Innes thinks that rats are more frequent predators of eggs than they are of chicks.

However, just when the chicks were half-grown, and the threat posed by rats was beginning to diminish, the drama unfolding on the tape moved into tragedy: the nest was discovered by a harrier.

In less than two minutes, the harrier carried off one chick and left the other one badly injured. When this second chick died, the kokako parents abandoned the nest, and that night the rat moved in again to scavenge the pathetic remains.

Rats are usually considered to be messy feeders, often leaving half-chewed remains and indigestible items scattered around. But by the following morning all that was left in the nest were the quills of two small pin feathers; no horny bill, no feet, no major bones.

Despite the sadness of the outcome, the primary object of the surveillance experiment had been spectacularly successful. The identities of two of the kokako’s nest predators have been confirmed, but what is also beginning to emerge from the tapes is that predation evidence is more difficult to interpret than was previously thought. At the second kokako nest, neither harrier nor rat had left any signs which would have been regarded as characteristic of the predator involved but even if the rat, for instance, had left the usual clues, they would probably have been misinterpreted. Without the video evi­dence, the rat would have been assumed to have been the killer, whereas its role in this case had only been that of a scavenger.

Nevertheless, rats are significant predators, and Innes says that it would be foolish to draw general conclusions from the slim evidence from only two nests. And, since kokako numbers continue to drop, more information is certainly needed, not just about predation but about the behaviour of kokako themselves. Next summer the security cameras will be out again in Rotoehu Forest.

Meanwhile, in nearby Pureora Forest, Chris Ecroyd, of the New Zealand Forest Research Institute, has been using electronic surveillance to solve a botanical mystery. For some time, Ecroyd had suspected a link between the rare plant Dactylanthus taylorii and the equally rare short-tailed bat.

A plant parasite,causes the formation of a flower-shaped woody growth on the roots of its host tree. (See “Flowers of Hades”, Issue 6)

Unfortunately, the popularity of these so-called wood roses as curios has contributed to the decline of the species. For many years, local collectors have dug them up, destroy­ing the parasite in the process. The flowers of the real Dactylanthus are of little interest to collectors other than as site markers, but for Ecroyd they yielded important clues to the solution of a botanical puzzle.

Dactylanthus flowers are drab, but they possess a strong musky scent and large quantities of nectar. What was the purpose of these attributes, wondered Ecroyd. They hardly seemed necessary for the heterogeneous selection of ants, flies and beetles that visited the flowers during the day. Ecroyd postulated the existence of an un­known specialist pollinator. An animal, he suspected. One which was large, nocturnal and used scent rather than sight to locate the nectar.

Video surveillance seemed to offer an ideal opportunity for the mystery visitor to reveal itself.

For the first few nights of the plant watch, rats hogged the limelight, almost destroying the male Dactylanthus flowers in their eagerness to get at the nectar. And while they also pollinated some of the female flowers in the process, Ecroyd doubted that they were the answer to his puzzle.

He felt he might have better luck on Little Barrier Island. But here, little Polynesian rats (kiore) completely destroyed the flowers, and there was still no sign of the creature he was hoping for.

Beginning to lose hope, Ecroyd returned to his original site in Pureora Forest. There, one April night, the wait was re­warded, and something else dropped into the frame. Scuttling through the leaf litter on its elbows and toes, the newcomer made its way over to the Dactylanthus. Pollen grains dusted its muzzle as it lapped up the nectar before flying out of the picture frame.

This was the first of many visits which short-tailed bats were to make to the plant that night—dramatic confirmation for Ecroyd of his theory that the bat and the plant parasite had evolved a close relationship over the millennia that they have coexisted here.

There’s a spin-off, too. Ecroyd speculates that if he can synthesise Dactylanthus nectar, it could be used as a lure to help locate elusive short-tailed bat populations.

Video surveillance looks like being in demand for many more wildlife research projects in the future.

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