• Summary
• Text account
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• Distribution map
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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). The population trend appears to be fluctuating, and hence the species does not 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.

Population justification
The global population is estimated to number c.300,000-1,500,000 individuals (Wetlands International 2015). The European population is estimated at 66,300-108,000 pairs, which equates to 133,000-215,000 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.50-10,000 wintering individuals in Taiwan; < c.1,000 individuals on migration in Korea; c.50-1,000 individuals on migration and < c.50 wintering individuals in Japan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Russia (Brazil 2009).

Trend justification
The overall population trend is fluctuating, although some populations are stable and others have unknown trends (Wetlands International 2015). The European population trend is estimated to be increasing (BirdLife International 2015).

Behaviour Northern breeding populations of this species are fully migratory whilst tropical breeders are more nomadic or locally dispersive (del Hoyo et al. 1996). The species breeds from May to early-June (Richards 1990) in monospecific colonies of 10-100 pairs (del Hoyo et al. 1996). After breeding it departs for the wintering grounds from late-July to September, returning again between April and May (Richards 1990). The species sometimes forages singly, but is more common in small groups or larger mixed-species flocks on passage and in the winter (Snow and Perrins 1998). Habitat The species utilises a variety of wetland habitats but shows a preference for freshwater marshlands with scattered pools, particularly where the surrounding vegetation is grazed by cattle or horses (Richards 1990). It frequents inland lakes, rivers, marshes, temporary pans (e.g. in Africa), artificial fish-ponds and drainage-ponds covered with water-lilies (e.g. in Italy) (del Hoyo et al. 1996), swamps, river pools, reservoirs, large dams, sewage-ponds, flooded saltmarshes, arable fields (e.g. in Australia) (Higgins and Davies 1996, del Hoyo et al. 1996) and rice-fields (del Hoyo et al. 1996). In Australia the species also occurs along the coast on estuaries, coastal lagoons, creeks in mangrove swamps (Snow and Perrins 1998) and tidal mudflats (del Hoyo et al. 1996). Diet Its diet consists of terrestrial and aquatic insects (del Hoyo et al. 1996) (e.g. Dytiscidae, adult and larval Odonata, Orthoptera, flying ants (del Hoyo et al. 1996) and mosquitoes (Richards 1990)), spiders, frogs, tadpoles, small crabs (del Hoyo et al. 1996), shrimps (Richards 1990) and small fish (del Hoyo et al. 1996). Breeding site The nest is a heap of aquatic vegetation (Richards 1990, del Hoyo et al. 1996) or dry grass (del Hoyo et al. 1996), placed either on floating and emergent vegetation over water 60-80 cm deep or resting on the bottom of very shallow water (del Hoyo et al. 1996). The species nests in colonies, neighbouring pairs spaced between 1 and 5 m apart (del Hoyo et al. 1996), and may forage up to 9 km away from breeding sites (more usually within 1 km) (del Hoyo et al. 1996).

The species suffers nest destruction from the invasive rodent species Myocastor coypus in Italy (Arduin 1997). Within its European range it suffers from the loss of natural wetlands to land reclamation, dry seasons and an increase in drainage schemes (Hagemeijer and Blair 1997), as well as the canalization of rivers (Tucker and Heath 1994). Additionally the following threats have been identified within its European range: increasing tourism and water sports near breeding colonies result in disturbance and the loss of nesting sites (Tucker and Heath 1994) and many nests are lost to adverse weather. It is affected by water quality and so pollution from insecticides and eutrophication are a threat (Martí and Moral 2004); In addition the intensification of fisheries and bycatch in fishing nets are issues (Golemansky 2011). Utilisation Large numbers of eggs are collected for sale and local consumption in India (this may be causing population declines in some areas) (del Hoyo et al. 1996), and fishermen collect eggs in Ukraine (del Hoyo et al. 1996).

Conservation Actions Underway
The following information refers to the species's European range only: Bern Convention Appendix II. The species has been included as a target species in three EU LIFE Projects.

Conservation Actions Proposed
The following information refers to the species's European range only: The species requires the maintenance of a network of water-bodies with well-developed emergent and floating vegetation to provide sufficient breeding habitat. These areas should be protected from disturbance by the establishment of buffer zones around them. Artificial, anchored rafts may be useful in providing nesting sites on intensively managed water-bodies (Tucker and Heath 1994).

Text account compilers
Malpas, L., Ashpole, J, Ekstrom, J., Butchart, S.

Contributors
Dowsett, R.J.

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Recommended citation
BirdLife International (2024) Species factsheet: Whiskered Tern Chlidonias hybrida. Downloaded from https://datazone.birdlife.org/species/factsheet/whiskered-tern-chlidonias-hybrida on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 23/12/2024.