Slender-billed curlew  (Numenius tenuirostris)

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1). Listed on Appendix I of CITES (3), and Appendix I of the Convention on Migratory Species (CMS or Bonn Convention) (4).

The slender-billed curlew is one of the rarest and least understood bird species that occurs in Europe (5). This medium-sized wader is a mottled brown-grey colour with white underparts that are marked with black spots on the flanks (6). The sexes are similar in appearance, although the female is generally larger in size (2). The long, slender beak is slightly decurved and tapers to a narrower tip than that of the curlew (Numenius arquata), and the long legs are a bluish-grey colour (2). The common name is derived from the soft 'cour-lee' call given in flight (6).

This migratory species has proven to be extremely elusive and despite numerous searches, neither the breeding nor wintering grounds have been satisfactorily discovered (7). The species was confirmed to breed near Tara in Siberia between 1914 and 1924 but no further nests sites have been seen (7). Slender-billed curlews historically over-wintered in North Africa and reports of large flocks were common in the region. Recently however, only one regular site has been identified (Merja Zerga in Morocco), and only a single bird was observed there in the winter of 1994 to 95 (7). As the species makes its annual journey from the supposed breeding grounds in northern Russia to wintering grounds in North Africa, it passes through a number of central and eastern European countries (6), and recently the species has also been confirmed from Northumberland in the United Kingdom (8).

During its migratory passage through Europe the slender-billed curlew uses a variety of different habitats including saltmarsh, steppe grasslands, fishponds, saltpans and brackish lagoons; wintering grounds show a similarly diverse range (7). Due to the paucity of sightings, the breeding site near to Tara, Siberia is assumed to represent typical nesting habitat and consists of taiga marsh at the northern limit of the steppe-forest zone (6).

Very little is known about the natural ecology and behaviour of the slender-billed curlew due to the elusive nature of this species. In 1914, a single nest was found which contained four eggs, and a colonial nest site containing 14 nests has also been reported (7). These birds feed by walking slowly and occasionally pecking at the surface until a food item is located (7). They have been reported to feed on earthworms, insects and molluscs (7).

The decline in the population of slender-billed curlews may have been due to the extensive hunting of waders for food in the early 20th Century (7). Curlews were a prime target due to their large size, and slender-billed curlews are often tamer than other species making them easy targets (7). The threat of hunting is reduced today but the loss and degradation of wetlands in the Mediterranean and North Africa may be a potentially serious threat (6). Population estimates based on migratory birds put the number of slender-billed curlew precariously low, at between 50 and 270 individuals (6).

The slender-billed curlew is protected in the majority of range states through which it passes and is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) (6). It is also listed on Appendix I of the Convention on Migratory Species (CMS), under which a Slender-billed Curlew Working Group (SbCWG) has been established (8). The group works to allow the cooperation of scientists and governments for the conservation of this species (8), and BirdLife International produced an Action Plan for the conservation of this species in 1996 (7). If the slender-billed curlew is to be saved from extinction, however, it is vital that the breeding sites are discovered so that any threats can be minimised and this enigmatic species can be better understood (7).

For more on the slender-billed curlew and conservation measures see:

• BirdLife International’s World Bird Database:
  http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3011&m=0
• BirdLife International (2000) Threatened Birds of the World. Lynx Edicions and BirdLife International, Barcelona and Cambridge.
• Gretton, A. (1996) International Action Plan for the Slender-billed Curlew (Numenius tenuirostris). Birdlife International, UK. Available at:
  http://ec.europa.eu/environment/nature/conservation/wildbirds/action_plans/docs/numenius_tenuirostris.pdf
• BirdLife International. (2001) Threatened Birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, UK.

Authenticated by BirdLife International Secretariat.
http://www.birdlife.org

• Brackish: slightly salty water.
• Colonial: relating to or belonging to a colony (a group of organisms living together in a group).
• Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
• Taiga: the sub-arctic forest of the high northern latitudes that surrounds the pole and is mainly composed of coniferous trees.

1. IUCN Red List (March, 2008)
   http://www.iucnredlist.org
2. Erritzoe, J. (1993) The Birds of CITES and How to Identify Them. The Lutterworth Press, Cambridge.
3. CITES (October, 2002)
   http://www.cites.org
4. Global Register of Migratory Species (March, 2008)
   http://www.groms.de
5. CMS (September, 2002)
   http://www.cms.int/species/sb_curlew/sbc_bkrd.htm
6. BirdLife International. (2000) Threatened Birds of the World. Lynx Edicions and BirdLife International, Barcelona and Cambridge.
7. Gretton, A. (1996) International Action Plan for the Slender-billed Curlew (Numenius tenuirostris). Birdlife International, UK. Available at: http://ec.europa.eu/environment/nature/conservation/wildbirds/action_plans/docs/numenius_tenuirostris.pdf
8. Birdguides (September, 2002)
   http://www.birdguides.com/birdnews/article.asp?a=35