Tools for protecting endangered species: eradication, translocation, triangulation

Abstract

This thesis is about the management of endemic New Zealand birds, which have become extinct on the mainland. The translocations of little spotted kiwi (Apteryx Owenii), from Kapiti Island to Tiritiri Matangi Island, provided an opportunity to assess kiwi behaviour in an artificially restored habitat. The transfer was successful in establishing a new breeding population of little spotted kiwi, with a high productivity rate of approximately 1 chick per pair each year. A study of bird numbers on Little Barrier Island following cat eradication is also presented. It is likely that the eradication of cats increased the survival of some species of ground nesting seabirds; however, it was difficult to attribute changes in passerine numbers to reduced cat predation over the fourteen years that passerines were monitored. A broad based approach to research was undertaken to research habitat use and range sizes of resident and newly released kiwi. This research was aided by the technique of triangulating the location of kiwi wearing radio-transmitters (by taking three bearings in the transmitter direction). Despite the precision of triangulation varying by 63 m, the 'spatial' information on kiwi showed home ranges to be three times biqger on Tiritiri Matangi Island (10.8 ha) than at the source location, and that newly released kiwi initially ranged over an area of 28.8 ha. Habitat use results suggest that the introductions of little spotted kiwi to areas of regenerating farmland with approximately ten-year-old regrowth habitat, dominated by tea tree with areas of bracken fern, are likely to be successful (if all predatory threats are absent). Despite the overall preferences for tea tree and bracken fern habitats, analysis at the individual level showed marked differences suggesting that habitat use is flexible. As were the choice of breeding sites, of which 83% were located in regenerating scrub or grassland habitat. These results show that relying on habitat use of relic kiwi populations is not useful in predicting habitat requirements. Genetic models typically assume equal founder contribution in the resulting population; however, this does not reflect reality. For example, the observed founder reproduction rates of a translocated group of saddleback (Philesturnus carunculatus rufusater) were skewed. Eight founders failed to leave offspring as only 16 of the 24 founders reproduced. Seven years after release, offspring produced from three founders accounted for 40% of the total observed saddleback population. In contrast to predictions, the population is self-sustaining, is reproducing at rates greater than at the source population, and has been used for the establishment of further populations. Considering populations of endangered species as a meta-population promotes the use of translocations to decrease the threat of extinction, as a meta-population has many advantages over a single population regardless of size. Since kiwi were widespread in pre-human times, I recommend that conservation managers should use translocations as experimental tests of habitat plasticity rather than to make prescriptions from limited knowledge. Therefore, managers of kiwi should also consider the value of islands or reserve areas of markedly different habitats.