Publications Archive

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.

Kaka (Nestor meridionalis), red-crowned parakeet (Cyanoramphus novaezelandiae), whitehead (Mohoua albicilla), tomtit (Petroica macrocephala), and bellbird (Anthornis melanura) have all recently been reintroduced to sites in or near Wellington city. Prior to or concurrent with these translocations, unmarked individuals of all five species were detected in forested reserves on Wellington peninsula. Based on the number of birds seen, and frequency of sightings, we suggest that red-crowned parakeets, whiteheads and bellbirds have established resident populations in some reserves independent of translocations. We attribute these successful re-establishments to the effective control of possums (Trichosurus vulpecula) and rats (Rattus sp.) undertaken by Greater Wellington Regional Council and the Department of Conservation.

The effects of time of day and observer vantage points on recorded waterbird species diversity and numbers of individuals of each species (especially New Zealand scaup (Aythya novaeseelandiae), the most common species) from a New Zealand wetland were analysed statistically and compared using rank abundance plots. There were significant differences between counts of total numbers of species, total numbers of individuals, and numbers of New Zealand scaup made from three observer positions and this effect was attributed to differences in observer elevation. Time of day had no significant effect on total numbers of species, total numbers of individuals of all species, and numbers of New Zealand scaup counted. However, rank abundance plots indicated a time of day effect on counts made at the least elevated of the observer positions. Overall, these effects were sufficient to introduce bias into waterbird counts and to require they be assessed during long-term monitoring programmes.