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.
Dispersal within New Zealand of Australasian shoveler (Anas rhynchotis), banded as ducklings in Otago (n=489) and Southland (n=392) during 1971-1979, was determined from the locations at which 180 were shot by hunters. There were no statistically sigruficant differences in recovery distributions of Otago and Southland birds either when recovered in their year of banding (y-o-b) or in all subsequent years combined (later). About 50% of total recoveries were made in the y-o-b and 2-thirds of these from within 200 km of the banding site. Recoveries in later years were more widely distributed than those made in the y-o-b. North Island recoveries were 28% of total recoveries and were from most large coastal and lowland wetlands as far as Northland, 1400 km from the banding site. Recovery distributions of ducklings were not significantly different from those previously determined for moulting adults banded in the same areas. However, ducklings in their 2nd year of life appear to be more distantly dispersed from their natal sites than during their 1st year or are adults from their moulting sites. We speculate that long distance dispersal may be undertaken mostly by birds that fail to breed in their natal regions in their 1st year of life, and that dispersing birds may become irregular breeders at varying distant locations.
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=0.08). 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.
Nesting pairs of brown skuas (Catharacta lonnbergi), black-backed gulls (Larus dominicanus), red-billed gulls (Larus novaehollandiae), white-fronted terns (Sterna striata), Chatham Island oystercatchers (Haematopus chathamensis) and shore plovers (Thinornis novaeseelandiae) were counted during 10 seasons on Rangatira (South East) and Mangere islands of the Chatham Islands. It was concluded that the small numbers of skuas, oystercatchers, and shore plovers on the islands was a result of habitat shortage, but that populations of the colonially-breeding gull and tern were constrained by food limitation in the surrounding seas. Whereas skuas, black-backed gulls, and terns nested in the open with conspicuous nests the other shore species on the islands had concealed nests. Comparison with nesting on Chatham Island, the New Zealand mainland, and subantarctic islands suggested that concealed nesting by red-billed gulls, oystercatchers and shore plovers was most likely in response to the presence on the islands of the predacious brown skua.
We investigated whether breeding frequency and breeding success of southern Buller’s mollymawks (Thalassarche bulleri bulleri) were influenced by breeding experience and pair bond duration, using data from annual checks at 3 study colonies at The Snares from 1992 to 2001. Most pairs bred annually irrespective of the experience and length of the pair bond, although the proportions that did so varied with pair type. Thus, breeding frequency (% breeding in consecutive years) was lowest among pairs of 1st-time breeders (77%). Breeding frequency of those pairs after their 2nd attempt (89%) became similar to that of established pairs together for at least 1 previous breeding attempt (88%), or newly formed pairs in which one or both birds had previous breeding experience (91%). Overall breeding success was 71% and, in established pairs, breeding failure (loss of egg or chick) was associated with reduced breeding frequency (83% compared to 91% when successful). Lowest breeding success (58%) was associated with the attempts of 1st-time breeders. Performance of these pairs improved until the 3rd attempt (81%), when it became similar to that of established pairs (73%) and newly formed pairs in which one or both birds had previous breeding experience (77%). Divorce was rare (1.1-3.5% annually). First-time and former breeders mated more frequently with birds of similar status (85% and 58% respectively) than expected assuming random pairings. When changing partner, as a result of divorce or death, the average interval before breeding again was 2.1 years for males and 2.6 years for females, and so, on average, each change of partner resulted in the loss of 1 breeding attempt. Thus, the time taken to obtain a new partner has a lifetime reproductive cost.