Movements and habitat connectivity of New Zealand forest birds: a review of available data

New Zealand's original forested landscape has been greatly fragmented since human arrival, limiting connectivity and habitat quality for forest-dependent fauna. We review the limited available information about forest bird movement behaviour, especially whole-year sociality and movement, natal dispersal, and pasture- and water-gap crossing. Most small insectivores (17 species) and North Island kokako are territorial year-round, but frugivore-nectivores (three species), raptors (two species), and volant parrots (four species) can be highly mobile, presumably to find scattered food. Natal dispersal is the main behaviour by which birds find new habitats and mates, but natal dispersal distances are unknown for half the species we review. There is limited information about species' ability to cross gaps between forests, and more is known about movement over water than pasture. We classify four species (North Island kokako, popokotea, South Island tieke, and North Island brown kiwi) as strongly gap limited, defined as currently unknown to cross water or pasture gaps larger than 500 m. A further eight species (mohua, tititipounamu, pipipi, weka, North Island tieke, kakaruai, toutouwai, and miromiro) are moderately gap-limited, with maximum observed gap-crossing distances of less than 5 km. Pending new data, these twelve species have most need of corridors or translocations to enable them to establish in new, safe, ecosanctuary sites. Habitat connectivity can be increased by strategic planting, but this also risks decreasing populations if birds emigrate from safe to unsafe sites. Many managed ecosanctuaries are too small to accommodate natal dispersal distances expected in continuous forest, so pest control is required at larger scale in the long term to restore natural movement patterns.