Effect of controlling introduced predators on kaka in Rotoiti Nature Recovery Project

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Summary

Stoats were introduced into New Zealand to control rabbits (Oryctolagus cuniculus) in the late 19^th Century but have since become a major predator of native bird species (King 2005). The South Island kaka is a forest dwelling parrot endemic to the South and Stewart Islands of New Zealand that is declining principally as a result of predation by introduced predators, including stoats (Heather and Robertson 1996; Wilson et al. 1998; Powlesland et al. unpublished).

The Rotoiti Nature Recovery Project (RNRP) is one of six New Zealand Department of Conservation (DOC) ‘Mainland Island’ Projects established in 1996 (Saunders 2000). The term ‘Mainland Island’ is used to designate areas of land on the main islands of New Zealand within which introduced pests are managed so as to create ‘islands’ of safe habitat for indigenous species, analogous to the offshore island sanctuaries that have provided safe refuge for many  endangered New Zealand endemics (See Saunders (2000) for a detailed account of the Mainland Island initiative). The RNRP has the goal of restoration of a beech (Nothogagus spp.) forest community, with emphasis on the honeydew cycle (Butler, 1998). The primary objective 7 is to reduce the abundance of certain introduced pest species, including stoats, to levels that allow the recovery of indigenous species, including the kaka (Butler, 1998). The RNRP has associated ‘non-treatment’ sites where no pest management is undertaken, which provide a control for management within the RNRP (after Butler, 1998). For information on kaka ecology and breeding biology see Heather and Robertson (1996), Wilson (et al. 1998) and Powlesland (et al. unpublished). For information on stoat ecology in New Zealand see King (2005).

From 1984 to 1996 Landcare Research scientists investigated the decline of South Island kaka in beech forest in the Duckpond Stream catchment of Big Bush Conservation Area (DPS), an area subsequently incorporated into the RNRP in November 2001 (Wilson et al. 1998). This study concluded that introduced predators, particularly the stoat, were the probable main cause of the decline of kaka populations on the main islands of New Zealand.

From 1997 to 2006, nesting success of the South Island kaka within the RNRP was monitored to assess the effect of mustelid (specifically stoat) control undertaken there. Kaka were selected for monitoring because they were known to be vulnerable to stoat predation (Wilson et al. 1998) and therefore would be expected to benefit from effective stoat control.