In the “Taxon plan for Northland brown kiwi

The Northland brown kiwi is unique in terms of its genetic makeup, behaviour and ecology, and is slightly larger and heavier than the three other brown kiwi taxa.

The Northland brown kiwi grows to around 40 cm in height and, as with all species of kiwi, there is a marked difference in size between the sexes. The adult females are, on average, about 30% heavier than the males, weighing around 2.7 kg. The males average 2.1 kg (Heather & Robertson 2005; Pierce et al. 2006; Hugh Robertson pers. comm.).

Female Northland brown kiwi have a bill length ranging from 117 mm to 156 mm, and male Northland brown kiwi have a bill length ranging from 86 mm to 119 mm (Colbourne & Kleinpaste 1983; Hugh Robertson, unpubl. data). It is not possible to distinguish a juvenile female from an adult male based on physical attributes alone (Heather & Robertson 2005), and so sexing of males and juveniles is best done from analysis of DNA in a sample of their feathers (Huynen et al. 2003).

Northland brown kiwi are usually monogamous and generally pair-bond for life. The male undertakes the preparation of the nest and the incubation of the eggs. On occasion, the female may be found in the nest, either by herself or with the male (Colbourne 2002) and/or chick(s) (Pete Graham, DOC Northland, pers. comm.). The nest is typically an excavated burrow, but may also be under vegetation or beneath logs and tree roots (Pierce et al. 2006).

Because of the relatively warm climate in Northland, and when conditions are suitable (i.e. there has been adequate rainfall), Northland birds demonstrate year-round breeding activity, although egg laying typically starts in June and July, with second clutches laid from October to December (Pierce et al. 2006). Eggs are laid about 3 weeks apart, with the first egg often left unattended during this time. They are then incubated for 75–85 days (Pierce et al. 2006) before the chicks hatch up to 13 days apart as fully feathered, largely independent miniatures of the adult. Northland brown kiwi generally produce two eggs per clutch, and can produce three clutches per season, although one or two is more usual (Burbridge et al. 2003).

Northland brown kiwi can successfully breed at 1 year of age (e.g. on Motuora Island, Rogan Colbourne, DOC Wellington, pers. comm.), but 3–5 years is more common (Hugh Robertson, pers. comm.). Northland kiwi have the highest productivity levels of all kiwi species, but they also have the highest adult mortality rates. Life expectancy of Northland brown kiwi is only 14 years compared with 40–65 years elsewhere in the country (Robertson et al. in press). This is largely a consequence of predation in unmanaged populations, particularly by dogs.

The preferred habitats of Northland kiwi are damp gullies in both indigenous and plantation forest, and dense shrubland. They also commonly utilise wetlands, gorse-dominant shrubland and rough pasture.

Northland brown kiwi are nocturnal, although young chicks are occasionally observed foraging during the day. They generally have multiple daytime shelters within their territory comprising burrows, fallen nīkau fronds, hollow logs, tight vegetation and slash from land-clearing or plantation forest harvest (McLennan et al. 1987).

Adult brown kiwi are territorial, and they will remain in an area for as long as suitable habitat is retained (Pierce et al. 2006). An adult bird will have a territory that tends to overlap with its mate’s. It will allow chicks and juveniles into its territory, but generally will not tolerate the presence of other adult kiwi (Colbourne & Kleinpaste 1983). Juvenile kiwi usually remain within 1 km of their natal site for their first 6 months of life before dispersing up to 20 km away (Pierce et al. 2006). Sub-adult kiwi will usually settle into a territory prior to their first mating attempt (Miriam Ritchie, DOC Northland, pers. comm.). Territories are largely maintained through vocalisation (Colbourne & Kleinpaste 1983; McLennan & McCann 1991), but birds will become combative if they need to.

Territorial boundaries and the number of kiwi in an area largely depend upon resource availability. Territory sizes may be smaller where there are more invertebrates and the soil is easier to probe. Territory placement is important for kiwi, particularly during dry summer months. Those without access to lower, wetter slopes and swamp margins are likely to lose condition (Colbourne & Kleinpaste 1983).

Kiwi diet predominantly consists of invertebrates such as insect larvae, wēta, crickets, centipedes, moths, earthworms and spiders, but it may also include occasional fruit, berries and leaves (Robertson & Colbourne 2003).

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