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Introduction
The foraging ecology and choice of feeding habitat of New Zealand's rarest breeding bird (Hansen 2005), the New Zealand Fairy Tern (hereafter: NZFT) Sternula nereis davisae (Gould 1843), have not been described to date. With a current breeding population of only nine pairs (four-year average 2008/2009-2011/2012; DoC internal reports) at only four known breeding sites (summary of Ferreira et al. 2005, Lagnaz 2010, Meagher 2010, Smith 2010, Zimmerman 2010), the New Zealand taxon is currently ranked as nationally Critically Threatened (Miskelly et al. 2008); with the species classified globally as "Vulnerable" (IUCN 2011). In spite of intensive protection, breeding monitoring and egg and chick management by the New Zealand Department of Conservation (Parrish and Honnor 1997, Hansen 2005) and community volunteer efforts, the NZFT still faces an extinction risk of 39% over the next 50 years (Ferreira et al. 2005).
While the factors identifying suitable breeding habitat have recently been assessed (Brooks et al. 2011), and feeding observations at nest sites indicate the potentially crucial prey spectrum during chick rearing (Parrish and Pulham 1995a), no data on foraging habitat choice and dependency, or foraging behaviour of the NZFT have been published to date.
Reproductive success in small terns has been shown to depend heavily on proximity of productive foraging areas (Perrow et al. 2011a, for Little Tern Sternula albifrons), and availability of high quality prey for chick provisioning (Dänhardt et al. 2011, for Common Tern Sterna hirundo). The conspecific Australian Fairy Tern (AFT) S. n. nereis has been reported to rarely travel beyond 2 km for foraging during the breeding season (Paton and Rogers 2009). Investigation of the feeding ecology of the NZFT is warranted to guide long-term conservation actions for the taxon.
We conducted a field study at Mangawhai Harbour, Northland, New Zealand during the 2010/2011 chick-rearing period (November-January) to address this gap in knowledge. We assessed the foraging ecology of the largest remaining breeding population at Mangawhai Harbour, where five out of the 10 breeding pairs nested on the neighbouring sand spit in the 2010/2011 season (DoC internal reports). Our study combined a specifically designed visual tracking regime that collated 140 hours of direct field observations to establish NZFT foraging habitat use, with...