VU
Fairy Tern Sternula nereis



Justification

Justification of Red List Category
This species is classified as Vulnerable owing to recent declines over much of its breeding range. Predation by introduced species, disturbance and inappropriate water level management are thought to have contributed most to this decline. However, data is patchy, and a clarification of trends in its strongholds may lead to its status being revised.

Population justification

Population estimates indicate that there are a few hundred pairs of Fairy Terns breeding in South Australia (in the Gulfs region) and Tasmania, 120-150 pairs in Victoria with up to 70 individuals in New South Wales. The statement cites a population of 1,600 pairs for Western Australia although this likely to be a significant under-estimate. All up the population of Australian Fairy Terns is currently considered to consist of between 5,000 and 10,000 individuals across all age classes. In New Zealand, davisae numbers 40-45 individuals. In New Caledonia, exul numbers 100-200 pairs. The total population is best placed in the band 2,500-9,999 mature individuals.

Trend justification
Data indicates a decline of 23% due to, perhaps most importantly, disturbance and predation.

Distribution and population

Sternula nereis occurs in Australia (subspecies nereis), New Caledonia (to France) (exsul) and northern New Zealand (davisae). Population estimates in the 2011 listing advice (Commonwealth of Australia 2011) indicate that there are a few hundred pairs of Fairy Terns breeding in South Australia (in the Gulfs region) and Tasmania, 120-150 pairs in Victoria with up to 70 individuals in New South Wales. The statement cites a population of 1,600 pairs for Western Australia although this likely to be a significant under-estimate. All up the population of Australian Fairy Terns is currently considered to consist of between 5,000 and 10,000 individuals across all age classes (Burbidge et al. 1996). Though it may be stable in Western Australia, numbers elsewhere in Australia have declined rapidly during the last thirty years. In New Zealand, davisae to three pairs in 1983 but, due to intensive conservation efforts has increased and in 1998, totalled 25-30 birds and 8-10 pairs over four sites. In 2006 this had increased to 30-40 individuals and 10 pairs (Parrish and Honnor 1997, Taylor 2000, S. Garnett in litt. 2007). By 2011, this had increased again to 40-45 individuals and c.10 pairs (P-J. Pridham in litt. 2011). In New Caledonia, exul numbers 100-200 pairs, but was formerly much more abundant (F. Hannecart per. M. Pandolfi in litt. 1999, N. Barre in litt. 2007). One small population in the Southern Lagoon of New Caledonia may be increasing (Baling et al. 2009). 

Ecology

It breeds on sheltered mainland coastlines and close islands, usually on sandy beaches above the high tide line but below where vegetation occurs (Higgins and Davies 1996). Breeding occurs at different times at different locations, but generally occurs from mid to late October until February (Higgins and Davies 1996), though exsul is a winter breeder both on the Coral Sea and in New Caledonia from at least May to December (Carter and Mustoe 2007, Barre et al. 2012). Adults have been observed to conduct post-fledgling parental care in New Zealand (Preddey 2008). It feeds on fish mainly by following shoals of feeding predatory fish (Higgins and Davies 1996) and also on small benthic fish as gobies, from shallow water in estuaries and harbours (I. Southey in litt. 2017). It lays one or two eggs. The oldest recorded individuals are at least 18 (New Zealand) and 17 years (Australia). Observations over one season on New Caledonia revealed a low rate of nesting success, with only one May to September (Barre et al. 2012) in five nests producing a fledgling (Baling et al. 2009). 

Threats

This species nests on low lying areas close to the sea and has been identified as a species vulnerable to flooding of nests due to future sea level rise, high tides and/or storms. Colonies in New Caledonia (Barré et al. 2012) have suffered high chick morality due to flooding during storms, strong winds have caused desertion of nests in New Zealand, and rising sea levels are also affecting Australian populations, with declines in Victoria attributed in part to severe weather reducing breeding success and killing adults (Dunlop 2015, Garnett and Franklin 2014). Fairy Terns are vulnerable to human disturbance which can cause nest desertion and reduce reproductive success if breeding is interrupted as later breeding attempts are more likely to fail due to adverse weather and predation (Dunlop 2015). Colonies have been abandoned in Victoria and along the west coast of Australia, which sustains the highest population concentration of Fairy Terns. This has been associated with increased access for humans, which results in direct destruction and desertion of nests due to human trampling, dogs, and vehicles (Baling 2008). Small populations in New Zealand and New Caledonia (Baling 2008, Barré et al. 2012) are also affected by human disturbance, despite intense management in New Zealand (New Zealand Fairy Tern Charitable Trust 2017).

Invasive species pose a significant threat to the Fairy Tern. Domestic cats Felis catus and dogs Canis familiaris, have been described as 'likely to harass' Fairy Terns near urban areas (Dunlop 2015). Cats were also seen to cause breeding failure on Rams island in Victoria (Lacey and O'Brien 2015). Red Foxes Vulpes vulpes are a significant predator of the Australian population of Fairy Terns. The majority of nesting attempts in the Younghusband Peninsula over 4 years were disrupted by foxes (Paton and Rogers 2009, Dunlop 2015). Invasive weeds reduce suitable nesting grounds, suspected to be one reason for the massive decline in the New Zealand population. Studies on Little Terns Sternula albifrons, which nest in very similar locations, show that breeding occurs on areas with only 20% vegetation cover (Hill 1991, Owen 1991). A more recent study has found Fairy Terns nesting at 82-85% (relatively flat, ground-hugging) vegetation cover, possibly an adaptation to human disturbance or nesting in sub-optimal habitat (Kohout et al. 2013). Yet, the taller introduced grasses reshape the habitat, creating a ground cover that is unsuitable for Fairy Tern nests.

Extraction of water from the Murray-Darling river system for human use has caused declines in prey numbers (Hardyhead fish) in the Coorong wetlands due to an increase in salinity, with the absence of breeding Fairy Terns from South Lagoon within Coorong thought to be directly related to a loss of certain Hardyhead species (O'Connor and Rogers 2013). The Coorong region holds a large proportion of the Western Australian population of Fairy Terns. Recovery occurred after 2009-2013, but droughts and extraction still threaten the region. It is likely that Fairy Terns moved to sub-optimal habitats with higher levels of pollution and/or more risk of damage from storms and tides (Paton and Rogers 2009). Coastline development in Australia, both for commercial and residential use, clears breeding sites and allows invasive predators such as foxes to access colonies (Dunlop 2015). Mangroves clearance in New Zealand would greatly reduce food supply for the already very restricted population (Ismar et al. 2014, Bellingham 2013).

Conservation actions

Conservation Actions Underway
Many colonies in Australia are regularly monitored, and intensive management has led to an increase in the population on New Zealand.

Conservation Actions Proposed
Monitor all breeding colonies annually to assess trends. Control introduced mammals and other nest predators at important breeding sites. Oppose developments which would encroach on breeding colonies. Restrict access to important breeding colonies.

Identification

25 cm. Very small white and grey tern with black cap. Upperparts pale grey; white forked tail; underparts white; legs orange-yellow; bill yellow-brown; white forehead with black crown, nape and line to eye. Similar species Very similar to Little Tern S. albifrons except upperwings more uniformly grey and forehead steep. Voice Flight call high pitched 'zwitt'.

Acknowledgements

Text account compilers
Moreno, R., Palmer-Newton, A., Stuart, A., Ekstrom, J., Anderson, O., Butchart, S., Garnett, S., Harding, M., Mahood, S., Martin, R., Calvert, R., McClellan, R.

Contributors
Burbidge, A.H., Holmes, D., Burbidge, A., Menkhorst, P., Barré, N., Christidis, L., Baker, P.E., Herman, K., Beauchamp, T., Saunders, D., Garnett, S., Dunlop, N., Ford, H., Southey, I., Wilson, D., Paton, D., Lacey, G.


Recommended citation
BirdLife International (2019) Species factsheet: Sternula nereis. Downloaded from http://www.birdlife.org on 24/06/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/06/2019.