Gray studied the last natural mainland population of kakapo in Fiordland in the 1970s. Between 1974 and 1977 all 15 male birds located occupied home ranges high on the sides of valleys in areas of diverse vegetation associated with the tree line or avalanche and alluvial fans. Track-and-bowl systems were frequently positioned on the crests of ridges and knolls on well-drained sunny slopes. Studies of feeding sign and of faecal content using cuticle analysis provided detail of kakapo diet, confirming the bird to be an herbivore. About 80 species of plants were eaten in Fiordland. The kakapo bill is adapted to crushing and extracting nutrients and retaining fibre which is expelled as distinctive ‘chews’. A preliminary study of the nutrients in kakapo food suggested that the birds selected the most nutritious plant parts and species.
The recent productivity and survival of the critically endangered kakapo (Strigops habroptilus) is summarised and its population trajectory in a variety of circumstances is modelled by simulation. Simulated kakapo population growth rates decline with decreasing intensity of management, and unmanaged kakapo on Codfish Island increase only slowly and have a significant risk of declining. Kakapo on islands where more than one fruiting species triggers their breeding have much higher growth rates than kakapo on islands where only rimu (Dacrydium cupressinum) triggers their breeding. The models predict that kakapo will reach a predetermined population milestone of 53 females in 2 – 6 years depending on the number of fruiting species that trigger breeding. At this milestone the intensity of conservation management will be reduced. Conservation management will be further reduced at a second predetermined milestone of 150 females in 19 – 37 years.
Results from an analysis of plant remains found in faecal droppings of kakapo (Strigops habroptilus) collected from 1981 to 1998 on Codfish Island (Whenua Hou) and Stewart Island, were analysed statistically to identify patterns in the birds’ diet related to breeding. Females were more likely to have eaten podocarp fruit or leaves of trees or shrubs; males to have eaten fern and Lycopodium rhizomes, monocots (in breeding years), and manuka fruit (in non-breeding years). Podocarp fruits were much more prevalent in kakapo diets in breeding than in non-breeding years. When podocarp fruits were available in breeding years, kakapo were less likely to have eaten several other foods. Conversely, Blechnum fern fronds appeared more frequently in the droppings of females in breeding than in non-breeding years. As podocarp fruits increased in prevalence in the diets of both males and females during the summers of breeding years, the incidence of many other foods declined. The incidence of Hall’s totara leaf in the diet of females increased during summer in non-breeding years, but decreased in breeding years.
We recorded the fate of brown kiwi (Apteryx mantelli) eggs collected from Northland forests for artificial incubation at Auckland Zoo. The hatchability of eggs of different ages were combined with known rates of egg losses in the wild to derive models which predicted that optimal hatching success (>64%) was when the oldest egg in a brown kiwi nest was 41-57 days old at the time the eggs were collected. Collection before this interval risked egg failure resulting from unknown developmental problems associated with artificial incubation of freshly-laid eggs, whereas later collection of clutches risked failures in the wild before the eggs were collected.
Information on the breeding ecology of Auckland Is snipe (Coenocorypha aucklandica aucklandica), Antipodes Is snipe (C. aucklandica meinertzhagenae), and Campbell Is snipe (Coenocorypha undescribed sp.) is summarised. Auckland Is snipe laid between Sep and Jan (peak late Nov), whereas Antipodes Is snipe laid from Aug to early Nov, with a 2nd pulse of breeding from late Jan to Mar. The 5 breeding events recorded for Campbell Is snipe were from clutches estimated to have been commenced between 11 Nov and 8 Jan. All 3 taxa laid 2 large eggs (each 19-22% of female body weight) in nests that were well concealed amid dense vegetation. Chicks left the nest soon after hatching, with each chick cared for by a single adult. Exceptions to this were adult Auckland Is snipe seen with 2 or 3 young chicks on 3 occasions. Chicks remained with adults until down-free and capable of flight. The only notable differences from the more thoroughly-studied Snares Is snipe (C.aucklandica huegeli) and Chatham Is snipe (C. pusilla) were the earlier breeding by Antipodes Is snipe, and its bimodal breeding season. Snipe were encountered more frequently on the Auckland Is (0.6 person–h-1 of walking on Adams I) than on Antipodes I (0.2 person–h-1) and this was also reflected in the frequency with which breeding events were recorded. We suggest that the impact of house mice (Mus musculus) on the invertebrate food supply available for snipe is the most plausible explanation for the much lower abundance of snipe on Antipodes I.
Bird species introduced to New Zealand from high northern latitudes are expected to change their breeding behaviour to conform to well-known geographic gradients in avian reproductive parameters. Here, we demonstrate reductions in average egg size and clutch volume for eight species of exotic passerine originating in the UK, and show that the magnitudes of these reductions appear to trade-off against reductions in annual variation in clutch size. Possible reasons for the trade-off are discussed.
Satellite telemetry can provide unique information on the biology and behaviour of mobile animals such as albatrosses. Determining areas of concentrated activity, essential resources and time-related changes in range use is of great importance for theoretical biology, practical conservation, and fisheries management. Utilisation Distributions (UDs), from a probabilistic model of the relative time spent by an animal in an area, were prepared using a kernel function in a Geographical Information System. Properties of the model were investigated, using satellite-tracking data from six northern royal albatrosses (Diomedea sanfordi) during eight over-wintering visits to seas off South America. We analysed UD areas and shape for different settings of the kernel smoothing parameter, a variety of location subsets associated with different sample sizes, sampling time periods and telemetry regimes. Small samples and intermittent transmission regimes reduced the UD range area. Individual bird data sets were combined to give comparable UDs. The UD model may help comparison of range areas and the identification of resource use, but they cannot identify an activity without additional information. For pelagic seabirds, UD preparation and interpretation require judgement and care.
Accounts of magpie Gymnorhina tibicen attacks on birds in New Zealand were collated from literature and a survey of the public, and then summarised to identify the frequency and characteristics of reported attacks on different species. Magpies were reported attacking 45 bird species. Species commonly found in rural habitats (e.g., harrier hawk Circus approximans, blackbird Turdus merula) where magpies are abundant were attacked most; however, a directly proportional relationship between species abundance in rural habitats and reported attack frequency did not occur. Species consuming similar foods to magpie tended to be attacked more often, probably because these foods are more abundant in rural areas. Attacks on smaller birds (e.g., grey warbler Gerygone igata) regularly (66%) resulted in death, but deaths declined as victim weight increased. Non-contact attacks were most common for the largest species (e.g., kereru Hemiphaga novaeseelandiae). Non-contact and non-lethal contact attacks occurred throughout the year while attacks resulting in death occurred mainly during the magpie’s breeding season (July to November). This study indicates that magpies can attack a wide range of species but fails to determine why (no one explanation satisfies all cases). Limitations of the dataset and future research to control these are discussed.
We analysed 13C and 15N isotopic enrichment in Australasian harrier (Circus approximans) eggshell and two discarded harrier feathers from Motunau Island, a regionally important seabird breeding island. Among the prey remains found at the nest was a prion (Pachyptila sp.) wing fragment and a predated blue penguin (Eudyptula minor). We combined isotope data from the prey remains, plus potential prey items obtained from the mainland, to reconstruct harrier diet and evaluate incorporation of seabird nutrients. During egg material formation, blue penguins made up a major part of the female harrier’s diet. During autumn, when feathers were re-growing, the two feathers (which may or may not have been from different individuals) gave very different results. The feather with the more marine signature was growing when harrier diet included a significant proportion of blue penguin and/or fairy prion (Pachyptila turtur) material. Formation of the other feather may have occurred while harrier diet was primarily terrestrial. Our results are indicative of the usefulness of stable isotopic analysis in elucidating nutrient flows and contributions to animal diet.
A survey was undertaken in the Te Waiiti Stream, Bay of Plenty, in summer 2002/2003, to identify blue duck (Hymenolaimus malacorhynchos) roost habitat. Thirty-six roosts were identified along 18.5 km of stream channel, averaging three roosts per blue duck pair. Stable undercut banks were most commonly used as roost sites (42%), followed by log jams along stream banks (25%). Large woody debris (LWD) was a component of 50% of the roost sites, and there was a positive relationship between LWD loadings in the stream channel and number of LWD roosts. All roosts provided overhead and lateral cover, most likely an adaptive response to current and historic avian predators, and all were located at the water’s edge. The location and composition of roosts provided easy access to the stream channel, discrete cover for rearing juveniles and for moulting, and daytime shelter. There were indications that channel morphology characteristics in the lower section of the survey reach may be limiting roost habitat availability and blue duck occupancy. Suitable roost habitat is a year-round requirement for blue duck and should be considered when evaluating their habitat.