144Wildlife Conservation Plan for Seabirds

144 Wildlife Conservation Plan for Seabirds

White-fronted Tern (Sterna striata)

TABLE Species information for the White-fronted Tern (Sterna striata)

The White-fronted Tern (Sterna striata) is a medium sized ‘commic’ tern with a long straight slender bill and a very long, deeply forked tail. It is the largest and bulkiest commic tern, proportionally similar to Common Tern (S. hirundo). The species is endemic to Australasia, breeding on the North and South Island of New Zealand, Stewart Island, the Chatham, Auckland and Snares Islands off the coast of New Zealand, and Flinders and Cape Barren Island off the north-east of Tasmania. It is also a winter visitor to Australia, from south Queensland to Tasmania and west to South Australia.

This species can be found in coastal areas, nesting on rocky or sandy beaches and shingle islands in rivers, also on coastal cliffs and deserted barges, often close to the surf. It feeds along the shore and in bays, and over oceanic waters in winter. It feeds almost exclusively on fish, but will also take shrimp, feeding in the surf zone or several kilometres out to sea. It often feeds in flocks by plunge-diving from 7-10 m with or without hovering, and by contact-dipping. Nesting takes place from October to December with most colonies containing 100-500 pairs, although solitary pairs are recorded at the edges of the range (del Hoyo et al. 1996).

In New Zealand, S. s. striata has been considered to have a population size of

5,000-20,000 mature individuals, and S. s. aucklandoruna was considered to have a population size of 1,000-5,000 mature individuals (Robertson et al. 2017). In Australia, (S. s. incerta) the breeding population is considered to be 120 mature individuals (Garnett et al. 2011), however, there have been no surveys since 1986 when 13 breeding locations were known (Garnett et al. 2011). Based on the subpopulation trends and subpopulation sizes from Garnett et al. (2011) and Robertson et al. (2017), the species may be decreasing. The overall decrease depends on the population size, but would fall in the range 5.2–29.1 per cent over 3 generations (30.3 years) and is considered Near Threatened by BirdLife International (BirdLife International 2019).

The species habit of nesting in densely packed colonies leaves it at considerable risk of predation by invasive predators (Mills 2013). It is also vulnerable to predation by native species, with an entire colony at Kaikoura (New Zealand) abandoned following chick predation by a single Northern Giant Petrel (Macronectes halli) (Mills 2013). There is also potentially a risk from the spread of the invasive weed Sea Spurge (Euphorbia paralias); however, this does not seem to be significant at present. It is possible that, in the future, the effects of climate change could have an adverse impact on food sources and breeding habitat.