Natal dispersal, habitat selection and mortality of North Island Brown Kiwi (Apteryx mantelli) at the Moehau Kiwi Sanctuary, Coromandel

Abstract

The Moehau Kiwi Sanctuary is one of five sanctuaries established in 2000 and managed by the Department of Conservation. The objective of the sanctuaries is to protect the most endangered kiwi taxa, and increase kiwi survivorship. Operation Nest Egg (ONE) is a programme utilised by the Moehau Kiwi Sanctuary for artificially incubating abandoned Kiwi eggs and captive rearing chicks until they begin to show a gain in weight. ONE chicks were then released back onto Moehau or adjacent protected areas. Kiwi populations are declining on the mainland at an average of about 3% per year in areas where predators of kiwi are not controlled. The main cause for this decline is chick mortality due to predation by stoats (Mustela erminea). During natal dispersal kiwi are known to disperse significant distances of between 5–20 km, and this has influenced the size of management areas needed for the protection of kiwi (10,000 hectares). The type of forest-cover is an important element in determining where management areas are located, as kiwi has preferences for certain forest types over others. This study conducted at Moehau, Coromandel, on the North Island Brown Kiwi advances our knowledge of kiwi by examining differences in rates and distances of dispersal among chicks, sub-adults, non-territorial and territorial adults, as well as between genders. This study investigates kiwi selective use of roost site types, ground-cover types, forest types and physiographical features. Addressed in this study are differences in dispersal, habitat selection and mortality among age-classes and between genders over the months of the year, and across elevations. Comparisons between ONE and wild-reared kiwi dispersal and mortality are included. Data were collected between 2001 and 2008 from observations of kiwi located during daytime hours. The data recorded included the grid reference, elevation, ground-cover type, forest type, physiography, and the type of roost site. The sample size for this study was significantly larger than for any previous studies thus enabling a greater confidence in estimated dispersal rates and dispersal distances, habitat selection and factors relating to mortality. All wild-reared kiwi displayed dispersal and were not philopatric to their natal area. Dispersal distances were found to be further than previously estimated, with the net distance of natal dispersal differing among age-classes, from an average of 834m (SE +/- 131) for kiwi chicks to 7,553m (SE = +/- 1167) for non-territorial adults. Female sub-adult kiwi dispersed further (7,215m) than male sub-adult kiwi (4,226m) (p = 0.04). The time taken to travel one km during natal dispersal ranged from an average of 131days/km (SE = +/- 9) for chicks to 89 days/km (SE = +/- 13) for sub-adults. Habitat selection has been observed in other studies on kiwi but not specifically for Coromandel North Island Brown Kiwi, and selection for ground-cover types by kiwi when roosting on the surface has never been previously studied. Roost site selection of kiwi differed among age-classes (p <0.001), between gender (p <0.001), and across elevations (p <0.001). Female kiwi were found more often in surface roosts (64%) than hole roosts (32%), and male kiwi were found at similar frequencies in holes (46%) and on the surface (47%). Sub-adults used holes to a greater extent as elevation increased, and selected for sub-alpine forest over broadleaf forest (p <0.001). This study is the first to recognise that selection of ground-cover types by kiwi differs among age-classes (p <0.001). Kiwi chicks were more often found on the surface under dead fern fronds and debris (39%) than other ground-cover types. The mortality rate was highest in chicks (33%), with predation responsible for 60% of these deaths; conservation management techniques were responsible for a further 20% of deaths; the remaining 20% of deaths were due to natural or unknown causes. Summer (December-February) was the season in which 81% of kiwi chick deaths occurred. The high proportion of deaths from monitoring techniques and the use of radio-transmitters (22%) indicates improvements need to be made to current management practices. ONE chicks were found to disperse shorter distances and had a greater mortality rate than wild-reared chicks. Therefore, recommendations are made for changes to ONE management practices. Further recommendations are made for the enhancement of kiwi habitat that could reduce kiwi mortality, and for increasing the habitat available to kiwi, thereby potentially increasing population sizes and/or densities.