The brown teal (Anas chlorotis) is a threatened duck endemic to New Zealand, whose single remaining stronghold is on Great Barrier Island. During a study at Awana from 1985 to 1987 it was concluded that the population was stable. We evaluated this proposition by analysing counts made at flocking sites between 1985 and 2001, examining their demography, and by developing an age-specific demographic model to predict the likely persistence time of the population. Numbers of teal at flocking sites declined between 1985 and 2001 though demographic variables did not change except for duckling survival rate, which increased from 26% during 1996 to 54% during 1999. Previous predictions of stability were based on an incorrect model and our model suggests that the brown teal population will halve every 4.1 years. The decline observed since 1987 could be halted by improving adult survival rate.
The reproductive biology of red-crowned parakeets (Cyanoramphus novaezelandiae novaezelandiae) was studied on Little Barrier Island (Hauturu) during the 1989/90 and 1990/91 breeding seasons. Nests sited in cavities of pohutukawa (Metrosideros excelsa) and puriri (Vitex lucens) trees accounted for all but 1 nest which was found in a hole in the ground. Breeding activity was recorded from Nov to Mar with peak egg laying in Dec. Mean clutch size was 7.0 eggs (range 4-9). Replacement clutches were rare and only followed the loss of young broods. Female parakeets were entirely responsible for incubation that lasted about 23 days. The nestling period averaged 40.8 days (range 32-49) with about a 30% probability of an egg resulting in a fledgling. The main cause of nestling mortality was starvation. Infestation of nests by mites and predation of nestlings were also occasionally recorded. Post-fledging mortality was high, particularly in the 1st 2 weeks, and was attributed mainly to aerial predators such as morepork (Ninox novaeseelandiae). Aspects of nest and roost site characteristics, brood reduction, mortality, and vulnerability to predation are discussed in relation to the conservation of the species.
More than 35,000 southern royal albatrosses (Diomedea epomophora) were banded on Campbell Island from 1941 to 1998. Recoveries of 2187 birds while breeding on Campbell Island during 1994-98 included 54 (2.5%) that were injured by their bands; over all years, 195 (3.4%) injured birds and 225 others with bands fitted incorrectly were reported. Injury rates were higher for birds banded as chicks (7%) than adults (0.5%). Untrained volunteer banders from the island’s meteorological station banded up to 5200 birds annually, and in some years bands were not closed properly. The partially open bands eventually embedded in the leg or ankle, crippling the birds. Six annual banding cohorts were responsible for 83% of injuries and almost half (n = 90) came from the 1979 cohort. Banding quality improved after 1982 and only two injured birds have been found from more recent cohorts. The band’s large circumference relative to its thickness may have contributed to it springing open with time, so a stronger band is recommended. For animal welfare reasons, a band repair operation should be conducted. If nothing is done, the situation will improve over the next 20-30 years as birds die, but regular band maintenance would prevent future problems.
The aim of this study was to associate the distribution of waders (Charadriiformes) with physical attributes of estuaries and map the distribution of estuaries that have the potential to support large diverse wader populations. Maximum wader abundance and the maximum number of species recorded (1983-1994) at 94 estuaries on the North Island, New Zealand were related to physical attributes of the estuaries using General Linear Modelling techniques. Parameters describing the estuary type, area, tidal influence, catchment area, catchment rainfall, intertidal area and temperature were used as independent variables. Anaiysis revealed strong positive relationships between the size and diversity of a wader population and estuary area. A negative relationship between catchment runoff and wader abundance and diversity existed in some estuaries. The model predicted that relatively small estuaries (100 to 999 ha) could support large, diverse wader populations if catchment runoff was low. A map of estuaries predicted by the model to support large diverse populations of wading birds is presented. This study highlights the value of large estuaries in New Zealand in maintaining large populations and high species diversity of migratory and nonmigratory waders.
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.