Publications Archive

Between 1986 and 1990,249 black petrels (Procellaria parkinsoni) close to fledging were transferred from Aotea (Great Barrier Island) 32 km west to Hauturu (Little Barrier Island) in New Zealand’s Hauraki Gulf. At the same time, 50 black petrels of similar age to those transferred were banded as controls on Hauturu and 229 on Aotea. Searches for these birds returning to breeding sites on both islands began in 1991 but three times more search effort was made on more-accessible Aotea. During their first 4.8 years of life at sea the only recovery came from off Ecuador (close to where two 6 year olds were also recovered). Since then to 2001,32 birds have been recaptured or recovered in New Zealand. Most were first recaptured at 5-6 years old and first breeding at 6-7 years old. A maximum of 42% survived to 6 years old. Survival rates of transferred and control birds were similar. The 1990 cohort had significantly better survival than did the 1986-89 cohorts, and this cohort, just 21% of the experimental birds, contributed 43% of chicks known to have been reared by experimental birds to 2001. Neither body mass at departure nor the El Niño-Southern Oscillation was clearly related to this differential survival. Most transferees returned to Aotea; none of the 1986-89 cohorts was found on Hauturu but 2 of the 3 1990 transferees that were recaptured returned to Hauturu. Given that fledglings were always transferred at a similar stage of development, the earliest transfer of heavy fledglings was the most successful.

The Westland petrel (Procellaria westlandica) is endemic to New Zealand, and nests within a restricted area of the West Coast of the South Is. Surveys of burrow occupancy rate in 2 colonies in 2001 using burrow-scopes showed an average of 21% of burrows contained a chick or egg. The rate was c. 50% of that recorded for other burrowing seabirds and surveyed using burrow-scopes. These findings may suggest that the breeding population may have declined in recent years, or that a large group of non-breeding birds maintain territories on the colonies. Further work is planned to test the 2 opposing hypotheses.

We investigated the habitat use and foraging behaviour of 3 South Island takahe (Porphyrio hochstetteri) family groups on Tiritiri Matangi Island, from Nov 1994 to Oct 1995. Takahe used habitats that offered abundant grasses, specifically grass/shrub mosaic and managed grass tracks, but open grassland was avoided. The preference was attributed to the higher risk of predation by Australasian harriers (Circus approximans) in this habitat as a result of a lack of sheltering trees or shrubs. Temporal patterns in habitat use reflected seasonal changes in food availability and breeding condition (age of chick). Most importantly, takahe family groups used the seasonally available grass seedheads in the grassland/shrub mosaic and the invertebrates in forest when chicks were young. The ability of Tiritiri Matangi to support takahe is likely to decrease as the suitable grass/shrub mosaic reverts to forest under the revegetation programme.

This study provides a first description of breeding biology of the South Island saddlebacks (Philesturnus carunculatus carunculatus) and the first comparisons with North Island saddlebacks (P.c. rufusater), using data collected from Ulva (Stewart Island), Breaksea (Fiordland) and Motuara (Marlborough Sounds) Islands, New Zealand. We found courtship and copulation behaviour to be similar to that of North Island saddlebacks. So too were nest locations, heights and materials, with nest materials determined by their proximity to the nest site. On Motuara and Ulva Islands, most nests were located in natural cavities (54% and 80%, respectively), while on Breaksea Island, 67% of nests were in flax (Phormium cookianum). In the recently established Ulva Island population, saddlebacks had a median and maximum clutch size of two and laid a maximum of two clutches. This contrasts with translocated island populations of North Island saddlebacks where up to four-egg clutches and four clutches per season have been recorded for pairs breeding in the first few seasons post-release. Incubation and brooding behaviour was like that described for North Island saddleback. A small number of yearlings bred successfully on Ulva Island (0.18 birds/ha), but no yearlings bred on Motuara (0.42 birds/ha) and Breaksea (0.42 birds/ha) islands.

Northern giant petrel (Macronectes halli) populations are thought to be increasing at some locations around the world, decreasing at others. The size and status of their breeding populations within the New Zealand region, in particular, is poorly understood: reliable population estimates have never been made at 3 of the 5 breeding locations. A survey of pre-fledging northern giant petrel chicks on Antipodes Island, New Zealand during Jan 2000 yielded a count of 130. The total population was estimated to be c. 230 breeding pairs. Because of an absence of accurate historical surveys, the status of the Antipodes Is population is unknown.

The South Island takahe (Porphyrio hochstetteri), an endangered flightless rail, has been released on 4 predator-free islands to reduce the risk of its extinction. To determine the ability of these islands to support takahe populations, we studied takahe home range size and carrying capacity on one of the islands. We plotted the location of 4 takahe family groups (13 individuals) from Nov 1994 to Oct 1995 on Tiritiri Matangi Island. Mean home range size (95% Minimum Convex Polygon) was 20.7 ha, and tended to be smaller when the proportion of suitable habitat within each home range was higher. We estimate that Tiritiri Matangi can support up to 8 breeding pairs, based on the availability of suitable habitat and estimated individual habitat requirements. However, this number is likely to change in the future depending on the influence of population density increases and successional habitat changes on takahe spatial requirements.