Publications Archive

Between 1961 and 1999 the number of adult sooty shearwaters found dead on beaches in northern New Zealand declined by about 64.4% and the number of fledglings by about 77.7%. Only 2 factors that we know about have been acting on the sooty shearwater population during the period studied and could have caused such a dramatic decline; a rise in sea temperature perhaps as a result of movement of the Sub-Antarctic Front and increase in harvest. Two other more recent phenomena, north Pacific fisheries mortality and climatic variation (El Niño Southern Oscillation and Pacific Decadal Oscillation), may be involved, but we cannot find any direct evidence of their impact in our data. The impact of this decline has been recently found on the breeding islands. More study is required to fully understand how weather, patrol frequency, deposition rate, persistence rate, and live bird numbers vary and interact. Deposition and persistence experiments similar to those reported from overseas need to be done in New Zealand.

The incidence of predation on house sparrows (Passer domesticus) and hedge sparrows (Prunella modularis) by captive brushtail possums (Trichosurus vulpecula), and the bird tissues consumed following predation, were recorded over 26 weeks in a facility where possums were housed in single sex groups. A total of 44 sparrow carcasses was recovered; on average 1.7 birds were killed per week (range 0-9 sparrows per week) in pens that each housed 8-12 possums. Tissue was eaten from fewer than half (48 %) of the birds killed. There were no significant differences in the incidences with which different tissues (brain, breast, legs, or viscera) were eaten. This study corroborates observations of bird predation by possums in the wild. Importantly, it shows that a high proportion of birds killed by possums are not eaten.

We compared the behaviour, energy expenditure, and food intake of male and female South Island pied oystercatchers, Haematopus ostralegus finschi, breeding in pasture and crop paddocks in Canterbury. In this monogamous species, females spent more time inactive than males (P=0.03) and there was a trend for males to spend more time in territory defence than females (P=O.O8). There were no significant differences in other behaviours and the sexes did not differ in their food intake rates. We used literature values for this species to estimate the energy expended in each activity and the energy expenditure rate over the breeding season. Despite the differences in the proportion of time spent in territory defence and inactivity by the sexes, males had a lower rate of energy expenditure than females over the breeding season (P=0.07). We suggest that behavioural differences are unlikely to compensate female South Island pied oystercatchers for their costs of gamete production and the difference in energy expenditure may reflect the uncertainty of paternity of males.