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Part B: Conservation Issues For Specific Species/Groups (continued)

4. Antarctic Tern (New Zealand) and Antarctic Tern (Indian Ocean) - Conservation issues

• 4.1 General Introduction
• 4.2 Taxonomy
• 4.3 Distribution
• 4.4 Population Size and Trend
• 4.5 Breeding Biology, Ecology and Diet
• 4.6 Threats specific to the Antarctic Terns
• 4.7 Issues and Recommendations
• 4.8 References
• Table 4.9: Summary of biological information for Antarctic tern (Indian Ocean) and Antarctic tern (New Zealand)

Antarctic Tern (New Zealand)	Sterna vittata bethunei
Conservation Status	Native subspecies
BirdLife International Status	Least Concern
EPBC Status	Endangered
Antarctic Tern (Indian Ocean)	Sterna vittata vittata
Conservation Status	Native subspecies
BirdLife International Status	Least Concern
EPBC Status	Endangered

4.1 General Introduction

The Sterninae, a sub-family of the Laridae, is comprised of the terns and noddies, a cosmopolitan group of seabirds, with narrow pointed wings and long pointed bills, They are mostly slimmer, longer-tailed and more aerial than gulls. The sub-family comprises about 42 species in seven genera.

The Antarctic Tern is a medium-sized tern (length 32-36 cm, wingspan 72-79 cm) with grey body and wings, white rump, a white deeply forked tail, and distinctive black cap that reaches down to the bill. The bill and feet are red, becoming brighter in the breeding season. It is found in the southern oceans and resembles the Arctic Tern from which it may be difficult to separate. However, many local Antarctic Terns are in breeding plumage when migrant Arctic Terns are in non-breeding plumage (Harrison 1983). The adult in breeding plumage is light grey above with black cap and white cheek stripe, white rump and tail, bright red bill, legs and feet. The adult in non-breeding plumage has a diagnostic combination of white forehead and crown, smudged grey underbody and dark red bill, legs and feet (Higgins and Davies 1996).

In Australian territory, the Antarctic Tern (New Zealand), Sterna vittata bethunei, breeds on Macquarie Island and the Antarctic Tern (Indian Ocean), Sterna vittata vittata, breeds on Heard Island.

4.2 Taxonomy

Higgins and Davies (1996) recognised 42 species in seven genera in the sub-family Sterninae. However, the number of genera varies, Moynihan (1969) recognised only three and others have recognised as many as 10. Higgins and Davies (1996) followed the arrangement of Christidis & Boles (1994) and Sibley & Monroe (1990). The monophyly of the genus Sterna, recognised by Higgins and Davies (1996), has been challenged by the electrophoretic study of Hackett (1989). There are three other subspecies of Sterna vittata, occurring in the South Atlantic Ocean, georgiae, tristanensis and gaini. (Higgins and Davies 1996).

4.3 Distribution

The movements of the Antarctic Tern are not fully understood due to confusion with other terns (Harrison 1983). This is particularly so at the sub-species level. Components of the populations of the sub-species vittata and bethunei appear to be partly migratory. The non-breeding range of all populations is poorly known.

Antarctic tern (New Zealand)

The Antarctic tern (New Zealand) breeds on Macquarie Island. The Australian population has been estimated at 50-250 mature adults (Garnett and Crowley 2000). However, Schulz and Gales (2004) recorded 24 breeding pairs in late November - early December 2003 - this census may have excluded some late-nesting pairs. There are no estimates of former abundance for the Australian population before exotic predators were introduced, but the population was apparently small in the early 20th century (Hamilton 1894, Falla 1937). Some individuals from the Macquarie Island population appear to remain in the area throughout the year (R. Clarke and M. Schulz unpublished), whilst others may disperse as far north as Australia and New Zealand. Otherwise little is known outside the breeding season (Garnett and Crowley 2000). Extralimitally, it breeds on Stewart Island, New Zealand and on New Zealand's subantarctic islands. The global population of this subspecies is considered to be less than 1,000 breeding pairs (Higgins and Davies 1996, Taylor 2000).

Antarctic tern (Indian Ocean)

The Antarctic tern (Indian Ocean) breeds only on Heard Island. Garnett and Crowley (2000) estimated the Australian population to comprise 50-250 mature adults, while Woehler (in press) estimated the Heard Island population to be between 100 and 200 breeding pairs. There are no estimates of former abundance for this population before the 1970s. Extralimitally, the Antarctic tern (Indian Ocean) breeds on subantarctic islands of the Indian Ocean (Crozet Is, Kerguelen Is, Prince Edward Is). The global population has been estimated to be less than 2,000 breeding pairs (Higgins and Davies 1996, Weimerskirch et al. 1989).

4.4 Population size and trend

Garnett and Crowley (2000) assessed Australian populations of the Antarctic tern (New Zealand) and Antarctic tern (Indian Ocean) as endangered. Both subspecies were estimated to have Australian populations of 50-250 mature adults, with 100 and 200 breeding individuals respectively (see also Schulz and Gales 2004). Woehler (in press) estimated the Heard Island population to be between 100 and 200 breeding pairs, which would suggest a maximum total population of approximately 500 individuals at HI. While these populations were considered to be stable, the restricted geographic distribution of both subspecies was considered precarious for their survival (Garnett and Crowley 2000). In Australia, the area of occupancy was estimated to be 2 km² for the Antarctic tern (Indian Ocean), and 3 km² for the Antarctic tern (New Zealand).

BirdLife International (2004) recently assessed the global conservation status Sterna vittata at the species level as Least Concern. This species has a large range, and the global population was estimated to be 140,000 individuals.

4.5 Breeding Biology, Ecology and Diet

Biological and ecological knowledge has been well summarised by Higgins and Davies (1990). Table 4.9 provides a summary of known biological information for the two subspecies.

Antarctic terns breed colonially, with colonies rarely exceeding 40 widely-spread nests at any one locality. At Macquarie Island most birds nest singly rather than colonially (G.Copson unpublished; Schulz and Gales 2004). The clutch is invariable one and eggs are laid in a shallow pebble-or shell-lined scrape on the ground on rocky beaches and glacial moraines. On Macquarie Island, the majority of nests are located on offshore stacks (Schulz and Gales 2004) in sites that are not frequented by seals. At Heard Island, laying occurs between October and January, and fledging of the chicks occurs between January to May (Downes et al. 1959). On Macquarie Island egg-laying is more protracted and extends to the end of December and possibly to March (M.Schulz unpublished), similar to that on New Zealand's sub Antarctic Islands (Bailey and Sorensen 1962).

The parents attend their young for several weeks after fledging, (Woehler and Clippingdale undated). During incubation an adult tern will leave its nest when an observer approaches within 25 metres, and call loudly to attract the attention of other members of the colony who return and add to the clamour (Downes et al. 1959, Woehler unpubl. data).

Antarctic Terns are gregarious feeders that fish in flocks of up to several hundred birds. Typically they forage inshore in the kelp zone up to 200m from the shore, where they feed on small fish and plankton (Higgins and Davies 1996). They also scavenge in the intertidal zone for stranded littoral organisms including small crustaceans, polychaetes and shell fish (Woehler and Clippingdale undated). They normally feed by hovering 2-15m above the sea, dipping or plunging into the water to catch their prey. At Macquarie Island birds are more regularly seen foraging alone (R. Clarke and M. Schulz unpublished), perhaps reflecting the small size of the local populations.

4.6 Threats specific to Antarctic Terns

Both subspecies of the Antarctic Tern are considered threatened because the populations are small, restricted in distribution, and therefore vulnerable to stochastic events such as storms and cyclones (Garnett and Crowley 2000).

Successful Antarctic Tern breeding is thought to be severely affected by disturbance and predation (Peter et al. 1988). Heard Island is predator free and hence there is no immediate threat posed by feral pests. However, maintenance of strict quarantine procedures is essential to ensure this situation remains. Cats on Macquarie Island were identified as possibly the most significant predator preventing pairs from breeding successfully (Rounsevell and Brothers 1984). Cats have since been eradicated from Macquarie Island, but rats still remain. Rats are thought to be the primary cause of failure to breed on the main island at Macquarie Island (M. Schulz and J. Lynn unpublished data) - the virtual restriction of breeding to offshore stacks may be due to the absence of rats at these sites.

Adult Antarctic terns co-operate to defend their colonies. However, skuas and kelp gulls still occasionally manage to take eggs or chicks from unattended nests in colonies following disturbance events (Woehler and Clippingdale undated).

Because of the Reserve status and isolation of both Macquarie and Heard Islands, there are no current threats to the avifauna from direct exploitation, competition from commercial fisheries or pollution. A total prohibition on commercial fishing within 13 nautical miles of Heard Island and within 3 nautical miles of Macquarie Island likely minimises against potential interactions with Antarctic terns at these sites. The shallow and inshore foraging behaviour of the Antarctic Tern also makes them unlikely candidates for interactions with commercial fishing operations.

Visitor access to breeding sites should be strictly controlled to minimise the impact on eggs and chicks as both are very cryptic and easily trampled by unwary visitors. The presence of visitors at nesting sites may also cause birds to leave eggs and chicks unattended, exposing them to the risk of predation by skuas and gulls.

4.7 Issues and Recommendations

• Continue monitoring of breeding population size and breeding success on Macquarie Island.
• Conduct monitoring program for breeding population and assess breeding success on Heard Island using minimal impact non-invasive techniques.
• Progress feral pest eradication program on Macquarie Island to mitigate possibility of rat predation on eggs and chicks.
• Continue rabbit control on Macquarie Island
• Ensure effective stringent quarantine programs at all sites to minimise the introduction of pests.
• All colonies to be managed in such a way that human disturbance is minimised.

4.8 References

Bailey, A.M. and Sorensen, J.H. (1962). Subantarctic Campbell Island. Proceedings of the Denver Museum of Natural History 10.

BirdLife International. (2004). Threatened birds of the world 2004. CD-ROM. Cambridge, U.K: BirdLife International.

Christidis, L. and Boles, W.E. (1994). The taxonomy and species of birds of Australia and its Territories. Royal Australasian Ornithologists Union Monograph 2. RAOU: Melbourne.

Downes, M.C., Ealey, E.H.M., Gwynn, A.M. & Young, P.S. (1959). The Birds of Heard Island. ANARE Report Ser.. B. 1.

Downes, M.C., Ealey, E.H.M., Gwynn, A.M. and Young, P.S. The birds of Heard Island. ANARE Reports Series B. Volume 1. Zoology. Antarctic Division, Dept of External Affairs: Melbourne.

Environment Australia. (2001). Macquarie Island Marine Park Management Plan, http://www.deh.gov.au/coasts/mpa/macquarie/plan/

Gardenfors, U., Rodriguez, J.P., Hilton-Taylor, C., Hyslop, C., Mace, G., Molur, S. & Poss, S. (1999). Draft Guidelines for the application of the IUCN Red List Criteria at national and regional levels. Species 31-32:58-70

Garnett, S.T. & Crowley, G.M. (2000). The Action Plan for Australian Birds 2000. Environment Australia: Canberra.

Hamilton, A. (1894). Notes on a visit to Macquarie Island. Trans. Proc. N.Z. Institute 27:559-579

Harrison, P. (1983). Seabirds: An identification guide. Sydney: Reed

Higgins, P.J. & Davies, S.J.J.F. (eds). (1996). The Handbook of Australian, New Zealand and Antarctic Birds. Volume 3. Oxford University Press, Melbourne.

Peter, H.-U., Bannasch, R., Bick, A., Gebauer, A, Kaiser, M. Moenke, R. & Zippel, D. (1988): Effects on anthropogenic influences on abundance and reproduction of Antarctic birds and seals in the southern parts of King George Island.- Fifth SCAR Symposium on Antarctic Biology. Abstracts,66

Rounsevell, D.E. & Brothers, N.P. (1984). The status of seabirds on Macquarie Island. Pp. 587-592 in Status and conservation. Pp. 609-625 in Status and conservation of the world's seabirds. ICBP Tech. Publ. No. 2. J.P. Croxall, P.G.H. Evans & R.W. Schreiber (eds). ICBP, Cambridge, U.K.

Schulz, M. and Gales, R. (2004). Breeding of the Antarctic Tern (Sterna vittata bethunei) on Macquarie Island. Notornis 51: 114-116.

Taylor, G.A. (2000) Threatened Species Occasional Paper No.16, Action Plan for seabird conservation in New Zealand, Part A, Department of Conservation, Biodiversity Recovery Unit, Wellington, NZ

Weimerskirch, H., Zotier, R. & Jouventin, J. (1989). The avifauna of the Kerguelen Islands. Emu 89:15-29

Woehler, E. & Clippingdale, M. (undated). http://www.aad.gov.au/default.asp?casid=1476

Woehler, E.J. (1991). The status and conservation of the seabirds of Heard Island and the McDonald Islands. ICBP Tech. Publ. 11:263-277.