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

Abstract

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.