Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The global population is estimated to number c.190,000-410,000 individuals (Wetlands International 2015). The European population is estimated at 36,000-53,000 pairs, which equates to 71,900-106,000 mature individuals (BirdLife International 2015). National population estimates include: c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in China; c.100-10,000 breeding pairs, c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Taiwan; c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Korea and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan (Brazil 2009).
The overall population trend is decreasing, although some populations have unknown or increasing trends (Wetlands International 2015). In Europe, the population size trend is unknown (BirdLife International 2015).
This species is breeding through much of Europe, scattered along the coast and inland in parts of Africa, in much of western, central and the extreme east and south of Asia, and in northern parts of Australasia. Migratory individuals expand the range to include most of the coast of Africa, the Arabian Peninsula, the western coast of India and most of the waters of south-east Asia and Australasia, including New Zealand. One seasonally breeding colony is also present on Hawaii (del Hoyo et al. 1996).
Behaviour This is a strongly migratory coastal seabird, which usually fishes in very shallow water only a few centimetres deep, often over the advancing tideline or in brackish lagoons and saltmarsh creeks (del Hoyo et al. 1996). It has the most inshore distribution of all terns. It breeds between May and July in solitary pairs or small monospecific groups usually of 1-15 pairs (rarely over 40 pairs) ,occasionally amidst colonies of other terns (Flint et al. 1984, Richards 1990, del Hoyo et al. 1996, Snow and Perrins 1998). Breeding may be timed to coincide with peak fish abundance (Perrow et al. 2006). Northern breeders depart the breeding grounds from late-July onwards (Richards 1990, del Hoyo et al. 1996), travelling first to moulting sites where they form large roosts before continuing southwards (Tavecchia et al. 2006). The species is gregarious throughout the year and usually feeds singly, in small groups or larger scattered flocks, congregating in many thousands on passage in small wetlands where fish fry are abundant (del Hoyo et al. 1996, Snow and Perrins 1998).
Habitat Breeding The species breeds on barren or sparsely vegetated beaches, islands and spits of sand, shingle, shell fragments, pebbles, rocks or coral fragments on seashores or in estuaries, saltmarshes, saltpans, offshore coral reefs, rivers, lakes and reservoirs (Flint et al. 1984, de Silva 1991, del Hoyo et al. 1996). It may also nest on dry mudflats in grassy areas, but shows a preference for islets surrounded by saline or fresh water, where small fish can be caught without the need for extensive foraging flights (de Silva 1991, del Hoyo et al. 1996, Snow and Perrins 1998). Non-breeding Outside of the breeding season, the species frequents tidal creeks, coastal lagoons and saltpans and may foraging at sea up to 15 km offshore (Urban et al. 1986, del Hoyo et al. 1996).
Diet Its diet consists predominantly of small fish (e.g. Ammodytes spp., roach Rutilus rutilus, rudd Scardinius erythrophthalmus, carp Cyprinus carpio and perch Perca fluviatilis) and crustaceans 3-6 cm long as well as insects, annelid worms and molluscs (del Hoyo et al. 1996). In Scotland, Little Terns feed mainly on small fish and invertebrates, including herring, sandeel, and shrimps (Crangon vulgaris) (BirdLife International 2000). In Portugal, birds were found to feed mainly on sand-smelts (Atherina spp.) and gobies (Pomatoschistus spp.), which were the most abundant fish species in the study areas (Catry et al. 2006). On Rigby Island, Australia, chicks were fed entirely on juvenile fish of the families Clupeidae, Engraulidae, Pomatomidae and Carangidae, including pilchard, southern anchovy and blue sprat (Taylor and Roe 2004).
Breeding site The nest is a bare scrape positioned on the ground in less than 15 % vegetation cover on beaches of sand, pebbles, shingle, shell fragments, coral fragments or rock above the high tide-line and often only a few metres away from shallow clear water (Flint et al. 1984, Richards 1990, del Hoyo et al. 1996, Snow and Perrins 1998). Alternatively, in more marshy habitats (e.g. coastal saltmarshes), the species may build a nest of shells or vegetation (del Hoyo et al. 1996). The species nests in small loose colonies, with neighbouring nests usually placed more than 2 m apart (del Hoyo et al. 1996).
Foraging range In Spain, 95% of foraging terns were observed less than 4 km away from the nearest colony (Bertolero et al. 2005). However, the foraging range of individuals varies according to whether they are currently breeding. In Norfolk, UK, birds with an active nest occupied a range of <6.3 km2 with a range span of up to 4.6 km, whereas failed birds ranged widely, travelling up to 27 km in a single foraging bout (Perrow et al. 2006). In Portugal, ranges were found to be significantly greater during incubation (April-May) than during chick rearing (June-July) (Paiva et al. 2007). Little Terns prefer channels and lagoons for foraging, rather than deeper marine habitats (Bertolero et al. 2005, Paiva et al. 2007). They also prefer areas with abundant resources, entrance channels and main lagoon channels with strong currents, and areas with alternative feeding resources nearby (Paiva et al. 2007). Areas subjected to strong human pressure and salt marshes are avoided (Bertolero et al. 2005, Paiva et al. 2007). The species tends to forage preferentially at low tide (Paiva et al. 2007).
Habitat loss and degradation through the development of foreshore poses a significant threat to the Little Tern, with relative sea level rises predicted due to climate change also threatening beach nesting habitats. The Red Fox Vulpes vulpes was noted as the main cause of breeding failure in New South Wales (Australia) in 1995/96 (NSW National Parks and Wildlife Service 2003), and a constant threat at various protected colonies in the UK, such as those in North Wales, where Common Kestrel Falco tinnunculus predation was also considered a factor (Gronant Little Tern Report 2015). The population of Red Fox in the UK has increased in size and range due to changing game-keeping practices, meaning they are likely an increased threat (Tapper 1992). In some parts of the range, birds are also vulnerable to nest predation by the Silver Gull Larus novaehollandiae. The Silver Gull population in New South Wales (Australia) has risen from a few pairs to over 50,000 (NSW National Parks and Wildlife Service 2003). Gulls are also likely to be problematic in other areas, with the culling of predatory gulls in Carleton, Quebec (Canada), key to fledging success (Magella and Brousseau 2001).
Little Terns are vulnerable to disturbance from birdwatchers, photographers and the general public, leading to nest failures (Gronant Little Tern Report 2015, BBC 2017). In the UK, 69% of the population breeds on mainland beaches in East Anglia and seems to negatively select for beaches with high disturbance level (Ratcliffe et al. 2008). Expensive interventions and volunteer effort is required to limit anthropogenic disturbance (Ratcliffe et al. 2008, Gronant Little Tern Report 2015). Egg collection is an ongoing threat, and has been recorded on multiple occasions at Crimdon (BBC 2017), one of the few colonies in the UK.
Conservation Actions Underway
The species is listed in Appendix II of the Convention on Migratory Species and is covered under the African Eurasian Waterbird Agreement. It is on Annex II of the Bern Convention. Within the EU, it is listed on Annex I of the Birds Directive. Protective measures, such as fencing-off sensitive nesting areas, erecting warning signs and wardening, are effective measures of increasing the breeding success of this species on sandy beaches (Richards 1990, Medeiros et al. 2007). There is also evidence that earlier breeders benefit more (i.e. have higher reproductive success) from protective measures, suggesting that conservation efforts can be maximised if concentrated earlier in the season (Medeiros et al. 2007). Breeding pairs are also known to be attracted to coastal locations where artificial nesting sites have been constructed (e.g. beaches of bare shingle and islands or rafts covered with sparse vegetation) (Burgess and Hirons 1992). A conservation scheme for the protection of breeding colonies of gulls and terns in coastal lagoons and deltas (e.g. Po Delta, Italy) involves protection from human disturbance, prevention of erosion of islet complexes, habitat maintenance and the creation of new islets for nest sites (Fasola and Canova 1996). The scheme particularly specifies that small bare islets of 0.1-0.8 ha with reduced vegetation cover (less than 30 %) and sward heights less than 20 cm should be maintained or created as additional nesting sites for this species (Fasola and Canova 1996). Within Europe, there are 258 Important Bird Areas identified across the species's range. Within the EU, there are 648 Special Protection Areas which include this species.
Text account compilers
Hibble, R., Butchart, S., Ashpole, J, Malpas, L., Martin, R., Calvert, R., Ekstrom, J., Stuart, A., Hatchett, J.
BirdLife International (2019) Species factsheet: Sternula albifrons. Downloaded from http://www.birdlife.org on 11/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 11/12/2019.