Diet overlap and potential competition between North Island brown kiwi chicks (Apteryx mantelli) and ship rats (Rattus rattus) for limited resources on Ponui Island, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

• Main Author: Shapiro, Lee Mark
• Format: Thesis
• Language: English
• Published: Massey University 2005
• Subjects: New Zealand > Ponui Island; Ponui Island (N.Z.); North Island brown kiwi; Rattus rattus; Black rat; New Zealand
• Online Access: http://hdl.handle.net/10179/8379

The introduction of mammals to New Zealand has devastated the native avifauna. Although not the most severely affected native bird species, all five species of kiwi (Apteryx Spp.) have sustained a severe loss of numbers and range. Kiwi have declined on the mainland from a failure to replace their numbers due to a high mortality rate of kiwi chicks. The main reason for this mortality is predation by introduced stoats (Mustela erminea). Many kiwi mainland populations have predator control enabling the recruitment of chicks. However a consequence of predator removal can be an explosion of rodent populations at control sites. Rodents do not directly prey on kiwi chicks but prey on invertebrates and these rodent population explosions may affect the number of invertebrates available to other forest dwelling animals such as kiwi. The potential exists for competition between rats and kiwi chicks as both feed on soil surface and leaf-litter invertebrates. Evidence from Kapiti Island where kiwi chick recruitment was high following rat eradication supports the competition hypothesis. The aim of the current study was to investigate the diet overlap and thus establish whether there was potential for competition for food between rats and kiwi chicks on Ponui Island in Auckland's Hauraki Gulf. Ponui Island is an ideal location for this research because there is a rat population and a high density of North Island brown kiwi, but no stoats. Kiwi chicks were measured and weighed weekly to determine growth rates, transmitters were changed every second week. Kiwi chick faecal samples were collected weekly from radio tagged individuals and the contents compared to those from ship rat stomachs, and the invertebrates available. Kiwi chicks and ship rats overlapped in the surface dwelling invertebrate component of their diets. Pitfall traps revealed no overall difference in the number and type of invertebrates found in bush and scrub habitat but weta and spiders were more abundant in scrub than bush, this was also the preferred kiwi ...