Justification of Red List Category
There are very few recent confirmed records of this species and sightings have become more and more infrequent, presumably as a result of declines caused by habitat loss and exploitation. No regular breeding, passage or wintering population is known, and the number of remaining individuals must be tiny. For these reasons the species qualifies as Critically Endangered.
The population is assumed to be tiny (fewer than 50 individuals and mature individuals) based on the lack of recent records. There are no recent confirmed sightings of this species within Europe, where it formerly regularly wintered. At the European level, it is classified as Critically Endangered (Possibly Extinct) (BirdLife International 2015). A record of an individual at Druridge Bay, Northumberland (Great Britain) in May 1998 was not confirmed (Collinson et al. 2014).
There are very few recent (uncontroversial) records of this species and they are becoming more infrequent so a continuing decline is suspected, although the rate is not known.
This species has only been confirmed breeding near Tara, north of Omsk in Siberia, Russia, between 1909-1925. It migrates west-south-west from its presumed breeding grounds through central and eastern Europe, predominantly Russia, Kazakhstan, Ukraine, Bulgaria, Hungary, Romania and the former Yugoslavia to southern Europe, Greece, Italy, and Turkey, and North Africa, Algeria, Morocco and Tunisia. It has also been reported from Slovenia, Uzbekistan, Turkmenistan, Saudi Arabia, and Yemen. Reports of birds staging in Ukraine persist but require confirmation. Regarded as very common in the early 19th century, it was already a rare bird by the 20th century, with regular records having dried up by the end of the century. Between 1980 and 1990, there were only 103 records involving 316-326 birds (BirdLife International 1999), and from 1990-1999, this dropped to 74 records involving 148-152 birds (BirdLife International 1999). Although there have been reports from Bulgaria, Ukraine and Uzbekistan of larger groups, most recent verified records have been of one to three birds, with the last nationally accepted record coming from Hungary in April 2001 (G. Buchanan and N. Crockford in litt. 2009, Oláh and Pigniczki 2010). In 1994, the population was estimated at only 50-270 individuals, but the paucity of recent confirmed records suggests it is now lower than 50 birds.
Behaviour: This species is migratory (del Hoyo et al. 1996). It is thought to breed in small colonies with nests between 2-3 m and 10-15 m apart (del Hoyo et al. 1996). Eggs have been found in May (del Hoyo et al. 1996). Early records often referred to the species as occurring in large flocks on migration and in winter. However, it is some decades since any sizeable flocks have been observed. The peak of the autumn migration appears to occur around September, with the spring migration peaking around March (Gretton 1991).
Habitat: Breeding The only known nests were recorded in bog-forest transition zones (Gretton 1991) on the northern limit of the forest-steppe zone in habitat more typical of taiga marsh. This may represent either a very specialised breeding habitat requirement, or an unusual use of habitat at the limit of the species's breeding range (Gretton 1991). Non-breeding On migration and in winter, a wide variety of habitats are used, including saltmarsh, wet grassland, steppe grassland, fishponds, saltpans, brackish lagoons, tidal mudflats, semi-desert, brackish wetlands and sandy farmland next to lagoons. Large coastal wetland complexes may be especially characteristic, and most records come from close to the sea (Buchanan et al. 2010). Where it winters inland it inhabits marsh areas fed with freshwater, but with areas of Salicornia indicating that the ground has a high salt content (Gretton 1991).
Diet: There is little information on its diet: birds at Merja Zerga (Morocco) fed on earthworms and tipulid larvae, while elsewhere insects (there is a suspiscion that orthoptera may have been an important food source [N. Crockford in litt. 2012]), molluscs and crustaceans have been recorded as prey.
Breeding site: A nest found by Ushakov in 1914 was constructed of dry grass with a few leaves of rush Scirpus but little or no sedge (Gretton 1991). The known nests were situated on dry areas of sedge and bog moss some distance from willow scrub or birch grove (Gretton 1991). An analysis of stable isotopes in feather samples from museum skins suggest that the main breeding area was located further south than the historically confirmed sites; in the steppes of northern Kazakhstan and southern central Russia between 48°N and 56°N, with a core area around 50°N (Buchanan et al. 2018).
Threats on the breeding grounds are unknown. Within its potential breeding range, the taiga has been little modified, the forest-steppe partially cultivated and much of the steppe modified by agriculture. Habitat loss in the wintering grounds is of unknown importance. There has been extensive drainage of wetlands in the Mediterranean and North Africa and potentially important areas in Iraq. The conversion of European wetlands and central European steppes to arable farmland may have heavily impacted the species by depriving it of important habitats during migration (Gretton 1991). Historically hunting was high, and may have been the key factor in its decline. Following the initial decline, breakdown of social behaviour patterns may have prevented recovery. Historically a gregarious species, smaller groups or individuals may have difficulty in locating suitable stop-over sites on migration (Gretton 1991). Individuals may join flocks of N. arquata, being led to unsuitable wintering habitat and rendered unlikely to find a mate (Gretton 1991).
Conservation Actions Underway
CITES Appendix I. CMS Appendix I and II. A Memorandum of Understanding, established under the auspices of the CMS, came into effect in 1994, and a working group was established in 1998 (Gallo-Orsi and Boere 2001). An international action plan was published in 1996. National action plans are in place in Italy (Nagy and Crockford 2004), Bulgaria and Ukraine. Several of the sites within the EU where the species has been recorded are designated as Special Protection Areas. There have been several international initiatives to survey passage and wintering sites (van der Have et al. 2001, Azafzaf and Feltrup-Azafzaf 2003, T. R. Cleeves in litt. 2006) and potential breeding areas (Gallo-Orsi and Boere 2001, Gretton et al. 2002), collate records (Gallo-Orsi and Boere 2001), protect key sites, raise public awareness (Azafzaf and Feltrup-Azafzaf 2003) and educate hunters.
Details of a 'last push' to locate any remaining populations (focusing initially on surveys of historical wintering areas) were announced at the Ninth Meeting of the Conference of the Parties to the Convention on Migratory Species in December 2008 (BirdLife International 2008, Crockford 2009, RSPB 2010). Surveys across the potential non-breeding range (from Morocco, perhaps as far as Japan) took place in 2009-11 with a particular focus on wintering and potential moult sites (G. Buchanan and N. Crockford in litt. 2012). The Slender-billed Curlew Working Group has developed a tool kit to assist people to identify and report Slender-billed Curlew in the field (available at: www.slenderbilledcurlew.net). If any can be found and caught then the sites used during the annual cycle could be determined by satellite tagging. An attempt to narrow down the search for breeding and moulting sites using stable isotope analysis and Strontium analysis of museum skins commenced in 2002 (Hilton 2003); results suggest that the main breeding area may have extended from southern central Russia into northern Kazakhstan (Nagy and Crockford 2004, G. Buchanan and N. Crockford in litt. 2012, Buchanan et al. 2018).
Conservation Actions Proposed
Continue to monitor key former and potential wintering and passage sites. Search for breeding grounds in the steppes of Kazakhstan, taking into account results of stable isotope analysis. Attach satellite transmitters to captured birds. Provide training in species identification along the migration route. Promote protection of habitat. Provide legal protection for this and similar species. Increase public awareness.
36-41 cm. Small, mottled brown-grey curlew. White underparts, adults marked with black heart-shaped spots on flanks. Decurved bill tapers to distinctly fine, sharp tip with narrow base and is completely dark in adults. Short, dark grey legs. Pale, barred inner primaries and secondaries contrast markedly with brown-black outer primaries. Always shows white under-wing coverts and axillaries. Rump virtually unmarked and tail has four to five dark bars on white background. At all ages lacks the cross-barred feathering of Eurasian Curlew N. arquata. Similar spp. Eurasian Curlew is larger and darker. Less contrast between dark feather centres and darker upperparts. Longer, more decurved bill, lacking fine tip. Lacks heart-shaped spots but often has scattered flank spots. Generally less patterned underwings. The legs are paler. N. a. orientalis is paler with whiter underwing. Whimbrel N. phaeopus darker with thicker bill and prominent, pale median crown-stripe. Paler N. p. alboaxillaris is difficult to separate. Voice Quiet cour-lee in flight. Like soft, accelerated N. arquata.
Text account compilers
Symes, A., Bird, J., Ashpole, J, Calvert, R., Benstead, P., Derhé, M., Hermes, C., Peet, N., Pilgrim, J.
Crockford, N., Hilton, G., Cleeves, T., Gallo-Orsi, U., Buchanan, G., Smith, K.
BirdLife International (2020) Species factsheet: Numenius tenuirostris. Downloaded from http://www.birdlife.org on 28/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/10/2020.