Sampling bias can have dire consequences for research. One potential source of bias is combining different sampling methods in the same study. However, combining methods can be unavoidable, for instance, when sampling method selection depends upon factors such as population density or terrain. A case at hand is the use of night-time encounter catching by people or daytime catching using certified dogs for studies of Apteryx mantelli, North Island brown kiwi, in Aotearoa New Zealand.
This paper examines, theoretically, how dispersal affects the viability of brown kiwi populations in protected areas of different size. Brown kiwi are threatened by introduced mammalian predators in mainland forests and are likely to persist only in managed forests where predators are controlled. In each protected area, the kiwi population will function as a net source, with an outflow of juveniles into the adjoining forest and minimal backflow into the reserve.
Incubation behaviour varies among the different taxa of kiwi. For North Island brown kiwi (Apteryx mantelli) and little spotted kiwi (A. owenii), only the male incubates the eggs, except for in the first week. Meanwhile, for Okarito brown kiwi (A. mantelli) and the tokoeka (A. australis), incubation is shared by both sexes. In addition, amongst southern tokoeka, family group members can assist with incubation to the extent that breeding males may take no part in incubation at all.
Kiwi have declined markedly in abundance and range since human settlement of New Zealand. Three of the four species are still extant in mainland forests, despite decades of co-existence with various introduced mammals. Little spotted kiwi is now probably confined to offshore islands. The role of introduced mammals in these population declines was evaluated by measuring the survival rates of adults, eggs and chicks of brown kiwi (A. mantelli) and great spotted kiwi (A. haastii) in mainland forests.