Petroica Longipes Research Articles

Predation at nests of two New Zealand endemic passerines; implications for bird community restoration

Predation at North Island Robin Petroica australis longipes and North Island Tomtit Petroica macrocephala toitoi nests was studied in New Zealand over the 1993/94 breeding season to determine impacts of predators. Infra-red, time-lapse video photography and sign left after predation were used to identify predators at nests. Accurate estimates of predation rates depended on early detection of nests. Previous studies of predation may have greatly under-estimated predation rates and therefore predation impacts. Predation was patchy and intense, resulting in failure to produce young in some territories despite up to ten nesting attempts. A maximum of 82% of nests were preyed on (n = 65; 95% confidence interval 72.4%?90%) and Ship Rats Rattus rattus were probably responsible for at least 72% (95% confidence interval 57.4%?84.4%) of predations. Nine of 24 territories lost breeding females, mainly to Ship Rats, which significantly impacted on population productivity. Ship Rat predation was equally intense at exposed and concealed nests (at the site and patch levels). Predation attributed to avian predators was strongly correlated with exposed nests (at the patch level). Restoration of New Zealand's threatened forest bird communities is dependent on a commitment to further research into the significance of different predators and predation impacts on bird populations.

Effects of familiarity on the outcome of translocations, II. A test using New Zealand Robins

Research on birds has shown that familiarity between mates and neighbours leads to lower aggression and higher reproductive success. This study addresses the hypothesis that founder groups used for translocations will do better if made up of individuals that are familiar with one another. The study involved a translocation of a territorial forest bird, the North Island robin Petroica australis longipes to an offshore island. I created both ‘familiar groups’ (made up of birds that had been adjacent to one another at the source location) and ‘unfamiliar groups’ (made up of birds that had been widely separated). I released the groups in separate forest patches on the island, and assessed the effects of familiarity on aggression, dispersal, survival and pair bonding. While the study was limited by the sample sizes possible, there was no indication that ‘familiar groups’ performed differently than ‘unfamiliar groups’, or that familiarity at the source location affected behavioural interactions following translocation. Post-translocation familiarity was clearly important, for aggression declined according to how long birds had been neighbours at the new location. There was little aggression in general over the first two to five weeks, the period when an effect of prior familiarity on aggression may have been most important. In addition, breakup of ‘familiar’ groups by dispersal meant that there was limited opportunity for interaction among familiar birds. These results suggest that familiarity within founder groups is unlikely to have strong effects following translocation.