The Disappearance of the Slender-billed Curlew

The Slender-billed Curlew (Numenius tenuirostris) was a migratory shorebird belonging to the sandpiper family. It once occupied a broad breeding and wintering range across Eurasia and parts of North Africa. Adults measured roughly 40 cm in body length with a wingspan of about 80 cm. The principal breeding region was believed to lie in western Siberia of Russia extending into northern Kazakhstan. During the non-breeding season the species ranged widely, occurring across eastern Europe, central Asia, the Mediterranean basin, and the coastal regions of North Africa.

The bird's plumage was characterized by dark brown spotting across the body. The head and nape bore dark brown streaks, while the underparts were generally pale or whitish. During the breeding season the spotting became more pronounced. Like many members of the sandpiper family, the species typically foraged in coastal lagoons, salt marshes, and other shallow wetland environments where it searched for small invertebrates.

Specimen of Numenius tenuirostris（Image source：Huub Veldhuijzen van Zanten， CC BY-SA 3.0 ）

The last confirmed observation of the Slender-billed Curlew occurred on 23 February 1995 at the Merja Zerga wetland in Morocco. A few additional reports were made between 1997 and 1998, but these sightings were never verified with clear photographic evidence. After that time, no reliable observations have been recorded. Using an extinction probability framework developed by the International Union for Conservation of Nature (IUCN), researcher Graeme Buchanan estimated that the probability the species has already gone extinct reaches approximately 96%. This level meets the statistical criteria used by the IUCN for classifying a species as extinct, suggesting that the Slender-billed Curlew most likely disappeared near the end of the twentieth century, even though it is still formally listed as “Critically Endangered” in current assessments.

Numenius tenuirostris（Image source：Henrik Grønvold，CC0 1.0 ）

Several interacting pressures probably contributed to the disappearance of the species. Habitat loss within its breeding grounds appears to have played an important role. Large parts of western Siberia and northern Kazakhstan underwent extensive agricultural expansion during the late twentieth century, which greatly reduced the amount of suitable breeding habitat. Hunting may also have been a significant factor. Historical accounts indicate that the species was frequently hunted in its wintering areas, and specimens were sometimes collected for museum collections. Such pressures likely intensified the decline of an already small and shrinking population.

The fate of the Slender-billed Curlew illustrates that even species with wide geographic distributions can vanish within a relatively short period of time. A closely related species occupying a similar ecological niche, the Eskimo Curlew (Numenius borealis), is now also classified as critically endangered and possibly extinct. Preventing other threatened migratory birds from following the same path requires coordinated international action and the use of modern conservation technologies.

The disappearance of the Slender-billed Curlew also highlights a broader lesson for conservation biology. Protecting only isolated locations or limited portions of a species' range is rarely sufficient. Migratory birds depend on a chain of habitats across their entire annual cycle. Effective conservation must therefore safeguard breeding grounds, migration routes, and wintering areas simultaneously. Only by addressing the needs of species throughout their full life cycle can long-term survival be ensured.

Author: Shui-Ye You

Reference:

Buchanan GM et al. (2025). Global extinction of Slender-billed Curlew (Numenius tenuirostris). Ibis.