Publications Archive

The natural diet of the kakapo (Strigops habroptilus) is exclusively herbivorous. The bird breeds synchronously with the heavy fruiting or “masting” of certain plant species, including rimu (Dacrydium cupressinum), at intervals of 2 – 5 years, and did so in 2002 on Codfish Island (Whenua Hou) in southern New Zealand. Crop contents of kakapo chicks of 10 – 30 and 31 – 43 days of age, and samples of rimu fruit (entire fruit, red aril, green aril and seed) were collected and chemically analysed for dry matter, organic matter, crude protein, fatty acids, amino acids, fibre, simple sugars and minerals. The crop content samples contained predominantly carbohydrates (76 – 81 % by dry wt.), crude protein (7 – 13 %) and fatty acids (6 – 7 %). Entire rimu fruit contained 7.2 % crude protein, 10.9 % fatty acids, and 78 % carbohydrate predominantly of cellulose, hemicellulose and lignin. The red aril, green aril and seed nutrient composition were similar with the exception of the seed fatty acid profile. There was a large degree of similarity in the nutritional composition of the entire rimu fruit and the crop contents, supporting field observations of the time that female kakapo were feeding almost exclusively entire rimu fruit to their chicks. The nutrient profiles provide the first detailed descriptions of the diet of growing kakapo chicks which can guide the development of supplements and artificial rearing diets for this species. The diet of kakapo chicks up to 60 days of age appears to have a low concentration of essential nutrients and high indigestible matter content when compared with other species, consistent with specialised anatomical features and foraging behaviour of this parrot.

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.

Recaptures of banded birds, and call counts, indicate a population of great spotted kiwi (Apteryx haastii) near Saxon Hut, Heaphy Track, in Kahurangi National Park has remained stable between 1987 and 2004. The number and the locations of occupied territories have changed little. Although few juveniles were encountered during searches with dogs, at least 10 of 22 territorial adults present in 1987 were replaced by a total of 12 birds over 17 years implying that recruitment kept pace with the annual adult mortality of about 4%. We suggest that the incidence of the main predators of kiwi (stoats, ferrets, cats and dogs) was low in this very wet area (rainfall >5500 mm/ year). Our findings support the current ‘Vulnerable’ conservation threat ranking for the species.

We experimentally evaluated the food hoarding behaviour of North Island robins (Petroica australis longipes) at Karori Wildlife Sanctuary, Wellington. Mealworms were offered to free-ranging pairs of male and female robins to evaluate whether their food hoarding behaviour was similar to previous observations of South Island robins. We also tested theoretical predictions derived in the Northern Hemisphere, which argue that competitively subordinate birds should hoard more food than dominant birds. Results showed that the food hoarding behaviour of North Island robins was similar to South Island robins, except that North Island robins repeatedly used the same cache sites, which is rare in South Island robins. Data did not support the prediction that competitively subordinate birds hoard more food than dominant birds. Males acquired most of the mealworms offered to birds during trials, and won nearly all aggressive interactions observed between sexes. Therefore, males appeared to be competitively dominant to females in winter. However, males stored over five times as many mealworms as females, which is opposite to theoretical predictions. We interpret the reluctance of females to cache food as a strategy to avoid food loss to competitively dominant males.

The Australasian crested grebe (kamana: Podiceps cristatus australis) is nationally endangered within New Zealand. A census, conducted on 24 January 2004 by 81 observers, recorded 300 adults and estimated a further 15 as present on 41 of the 93 lakes counted. Assuming approximately 30 grebes to be present on lakes not counted, the national population of adult crested grebes is estimated to be 340-350. This is 40% higher than the population recorded in 1980. In addition, 75 juveniles were counted on 18 lakes. As in the 1980 survey, approximately 55% of the adult crested grebes were recorded on Canterbury lakes. A significant regional change has occurred with birds now present on lakes in Otago, absent from Nelson lakes, and in reduced numbers in Marlborough, North Canterbury, Westland and Fiordland. In addition, a significant decline has occurred at Lake Alexandrina, one of the strongholds identified in the 1980s. Forty percent of the present adult population was recorded on two lakes, Lake Heron and Lake Hayes. We identify priority sites where management to reverse declines could be implemented and we recommend a suite of management actions.

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.

We studied activity rhythms at a gentoo penguin (Pygoscelis papua) colony at Cierva Point, Antarctic Peninsula, during the 1992-93 summer. We counted the number of penguins crossing a specific point on their route to and from the colony. Penguins showed a strong daily rhythm of activity, with a two-peak pattern for those leaving the colony and a one-peak pattern for those returning. The peak of penguins departing to sea was at dawn, with a secondary peak in the afternoon which was coincident with the peak of returns. Although this behaviour could be explained by nest relief schedules, the pattern remained once crèches had formed. The main peak of departures strongly correlated with sunrise, which might support the existence of a light signal synchronizing activity. Even though an external factor could be triggering movements, an endogenous circadian clock might drive both patterns.