Responses of the Maud Island frog, Leiopelma pakeka, to artificial displacement

Abstract

Movement is one of the most important behaviours exhibited by an animal and can have a great deal of impact on an individual's success. lt is also an important factor to consider in the conservation management of a species. Following the 2005 re-introduction of one hundred and one Leiopelma pakeka from Maud Island to Long Island, Marlborough Sounds, New Zealand, several aspects of their movement were examined. I looked at the behaviour post-release on Long Island as well as frog movements following short-distance displacements within the source population. In addition, the recolonisation of individuals following the removal of resident frogs from Maud Island was investigated. A review of amphibian and reptile re-introductions, translocations, and supplementations published from 1991-2006 was also undertaken.

By resighting frogs that were moved to Long Island during an inter-island reintroduction, I determined that L. pakeka tended to move downhill from the release site. Eight months after release, dispersal distances ranged from 0.28 to 15.52 m. Bearings taken by frogs were not uniformly distributed with mean bearings being in a southerly direction. There were no significant differences in the directions or distances moved by frogs in the long-term based on whether they were released with neighbours or non-neighbours.

Short distance displacements on Maud Island showed that L. pakeka were able to home, though this ability declined with relocation distance. Arena experiments also showed that frogs were able to move in a homeward direction even in the absence of visual and chemical cues from their environment. This tendency to move in a homeward direction was evident during the breeding season but not earlier in the year.

To test the recolonisation ability of L. pakeka, resident frogs were removed from a plot on Maud Island. The area was invaded by other individuals and frog densities returned to levels within the range of other undisturbed areas on Maud Island after only six months. After one year, the relative abundance of individuals within the eight quadrats in the plot was no longer significantly different from the initial distribution of resident frogs, indicating that the spatial distribution of frogs had also returned to normal. Invading adult frogs had significantly lower body condition indices and snout-vent lengths than resident frogs. Proportions of subadults and adults were similar between recolonising and resident groups.

A review of worldwide amphibian and reptile re-introductions, translocations, and supplementations since 1991 showed that only 29.4% of the projects reported resulted in success. This was higher than the success rate of herpetofauna relocations reviewed in 1991. Factors including motivation for and decade of relocation were related to the project outcome.

If re-introductions, translocations, and supplementations are going to be used for the conservation of New Zealand's native frogs, groups involved need to realise that this is not a fail-proof method. In order to make these relocations more successful, factors such as homing and post-release movement in addition to many others should be taken into consideration. Also efforts should be taken to restore or create habitat adjacent to current frog populations that are habitat-limited, as Leiopelma frogs appear to easily colonise vacated habitat.