Causes of mortality at nests of ground-nesting birds in the Upper Waitaki Basin, South Island, New Zealand: a 5-year video study

Abstract

We used video cameras over 5 years to quantify causes of mortality at 172 nests of three species of ground-nesting birds that nest on braided riverbeds of the Upper Waitaki Basin, South Island, New Zealand. The species were banded dotterels Charadrius bicinctus ( n=114), black stilts Himantopus novaezelandiae ( n=23), and black-fronted terns Sterna albostriata ( n=35). Of 77 recorded lethal events (excluding four desertions caused by us), 66 involved deaths of only eggs, and 11 involved deaths of adults and/or chicks, and/or eggs. The main predators were cats Felis catus, hedgehogs Erinaceus europaeus, and ferrets Mustela furo, which were responsible for 43, 20, and 18% of lethal events, respectively. Cats were the only predator species to take adult birds. We recorded only two avian predations: a harrier Circus approximans took a chick and a hatching egg from one nest, and an Australian magpie Gymnorhina tibicen ate chicks at one nest. Other causes of mortality were incubating adult birds, floods, and sheep Ovis aries. Each accounted for <4% of lethal events. Ninety percent of visits (151 of 168) by predators or potential predators happened between sunset and sunrise. We found no evidence that video cameras or infra-red lighting influenced predation rates during 2 years of testing for such effects.