In the “Taxon plan for Northland brown kiwi”
Prior to human arrival, kiwi were found in high numbers throughout New Zealand, with the distribution of Northland brown kiwi likely extending throughout Northland from the Aupouri Peninsula in the north to the Auckland region in the south. By the 1970s, their range was limited to mostly forest and shrubland areas between Awanui and the Brynderwyn Ranges (Pierce et al. 2006) (Fig. 1). Unfortunately, the 1970s and 1980s saw a rapid decline throughout much of Northland, resulting in the localised extinction of kiwi from many areas, largely as a consequence of predation from introduced mammals (Pierce et al. 2006). In 1996, McLennan et al. (1996) calculated that North Island kiwi had probably declined in abundance by at least 90% in the previous 100 years.
The current distribution of Northland brown kiwi extends from Whakaangi in the north to the translocated population at Tawharanui Open Sanctuary in the south (Fig. 1). They are also present on offshore islands from the Bay of Islands in the north to the Hauraki Gulf in the south. Islands with kiwi include Motukawanui, Motuarohia Island (Roberton Island), Moturua, Limestone (hereafter referred to as Matakohe-Limestone Island), Kawau and Motuora (Colbourne 2005). Kiwi are all but extinct from southern Northland and the Aupouri Peninsula in the far north.
A mixed-provenance population exists on Ponui Island (Chamberlins Island) (hereafter Ponui Island), of Northland and Hauturu/Little Barrier Island founders. There are also unconfirmed reports of kiwi present in northern parts of the Auckland region around Leigh and Tapora (Thelma Wilson, DOC Northland, pers. comm.), the latter as a result of translocations in the 1980s.
The 25 population clusters of Northland brown kiwi are distributed within seven main geographical groupings (Pierce et al. 2006):
- Bay of Islands
- Western/Kauri Coast—Opouteke, Tutamoe-Trounson-Waipoua area
- Eastern—coastal locations from Russell Peninsula to Whangarei Heads
- Southern Central—Purua-Marlow-Motatau and Pipiwai areas
- Tawharanui Open Sanctuary
- Offshore islands
Northland is considered to be a stronghold for brown kiwi, as it contains around 32% of the total New Zealand population. If current management effort is maintained, this population is expected to climb from 8000 birds in 2008 to 8500 birds by 2018. This estimate is based on a 3% annual decline for unmanaged populations and an annual increase of 9% in managed locations (Hugh Robertson, unpubl. data in Holzapfel et al. 2008).
This small predicted increase assumes that current efforts are simply maintaining the population rather than leading to further recovery. As noted in the Kiwi Recovery Plan (Holzapfel et al. 2008), while only 20% of Northland birds are currently under management, their increase approximately equals the assumed decline in the unmanaged populations.
The population potential for Northland brown kiwi in managed habitats is not well understood. There are historical records from the late 1800s that estimate densities of 0.4–1 adult kiwi per ha in North Island forests (Buller 1877, 1888 in McLennan et al. 1996). These densities are not unheard of today, with current densities of one pair per 2–5 ha in well-managed Northland forests. Pierce et al. 2006 estimated that if all components of a forest were well managed, 1000–2500 ha could potentially accommodate 500 pairs.