The slender-billed curlew (Numenius tenuirostris) is a species of bird that is no longer alive. It once lived in parts of Eurasia and North Africa. Studies suggest most of the birds bred in the Kazakh Steppe, even though some were found in Siberian swamps. These birds migrated, spending their winters in shallow freshwater areas near the Mediterranean Sea. Occasionally, they were seen in places like western Europe, the Canary Islands, the Azores, Oman, Canada, and Japan.

In November 2024, scientists declared the slender-billed curlew extinct worldwide. The last confirmed sighting of the bird was in Morocco in February 1995.

Description

The slender-billed curlew was a small bird, 36–41 cm (14–16 in) long, with a wingspan of 77–88 cm (30–35 in). It was about the same size as the Eurasian whimbrel but had plumage more similar to the Eurasian curlew. The adult during breeding season had greyish brown feathers on its back, a whitish rump, and a lighter lower back. Its underparts were white and heavily streaked with dark brown. The sides of its body had round or heart-shaped spots. In non-breeding plumage, the bird looked similar but had fewer spots on the sides. Males and females had the same colors, but females had longer bills, which helps reduce competition for food between the sexes. Juvenile birds looked similar to adults, but their sides had brown streaks, and the heart-shaped spots appeared only later in their first winter.

Compared to the Eurasian curlew, the slender-billed curlew had a whiter breast, tail, and underwing. Its bill was shorter, thinner, and slightly straighter at the base. The Eurasian curlew had arrowhead-shaped spots on its sides, while the slender-billed curlew had round or heart-shaped spots. The head pattern of the slender-billed curlew had a dark cap and a whitish stripe above the eye, similar to the Eurasian whimbrel. However, the Eurasian whimbrel also had a central stripe on its head and a more clearly defined pattern, making the slender-billed curlew’s pattern harder to see in the wild.

This bird showed more white than other curlews. However, the white underwing has been overemphasized as a key feature for identification. Instead, recent studies highlight other traits, such as the dark underside of 4 to 6 outer wing feathers, darker legs (black in adults or grey in younger birds), and a white tail with fewer dark bars.

The call of the slender-billed curlew was a short, high-pitched "cour-lee," similar to the Eurasian curlew but more melodic. Its alarm call was a quick "cu-ee." The only known recording of this bird was made by French ornithologist Claude Chappuis. After his death in 2021, his collection, including the slender-billed curlew, was donated to the Macaulay Library at Cornell University in Ithaca, New York.

Distribution

The only known places where the slender-billed curlew is confirmed to have bred are a small area of wetlands north of Omsk, Russia, between 1909 and 1925. Scientific studies suggest that the main breeding area of this species was a narrow region in Kazakhstan near the 50th parallel north. This area is mostly steppe, with some parts covered by forest steppe.

In recent years, the bird mostly traveled to the Mediterranean and southern Arabia. Some reports mention sightings in the northern parts of the Persian Gulf, Kuwait, and Iraq. Historical records show the bird was also seen in other areas. For example, an ornithological dictionary from Gibraltar, written in 1895, notes that the slender-billed curlew was observed as a passing migrant in Málaga, Spain.

Behaviour

Little is known about how the slender-billed curlew breeds. However, the nests that have been seen contain four eggs each.

This bird mainly eats small animals by using its bill to search through soft mud. It also sometimes picks small prey from the ground when possible. During times when it is not breeding, the slender-billed curlew often stays in groups and is commonly found near other similar species, such as the Eurasian curlew.

Decline and extinction

Over many years, the number of slender-billed curlews decreased steadily. By the late 20th century, the birds were extremely rare, with fewer than 50 adult birds remaining. The last confirmed sighting of the species was in Morocco in 1995.

The last well-documented nest was found in 1924 near Tara in Omsk Oblast, Siberia (57°N 74°E). Since then, the nesting areas of the species have not been located, even after several searches. This is difficult because the search area covers more than 100,000 square kilometers. The decline of the species is also shown by the absence of wintering birds at sites in Morocco where they were once regularly seen.

The reasons for the species’ decline are not fully understood. Both hunting and habitat loss have been suggested as possible causes. Hunting of the bird was recorded as late as the 1980s in the Merja Zerga wetlands in Morocco, one of the last wintering areas for the species. As the bird became rarer, hunting pressure may have increased because people sought its feathers. Specimens were found in markets in Italy and other parts of Southern Europe, likely shot during migration.

The predicted breeding area of the bird in the Kazakh steppes was changed into farmland as part of the Soviet Virgin Lands campaign in the 1950s. This campaign caused the loss of habitat for many bird species, including the slender-billed curlew. However, the decline of the species began decades before the farming campaign. Habitat changes into farmland in the region had already started in the 19th century. Wetlands in wintering areas, such as Morocco and Hungary, were also converted into farmland during the same period, which likely contributed to the decline.

In 1995, 20 birds were reported in Italy, but this record is now considered unreliable. Photographs and recordings confirmed the birds were actually a different species, Numenius arquata orientalis (Kirwan et al., 2015). A potential sighting of a young bird was reported in England in 1998, but it was later removed from the British List after a review.

Since then, the species has been seen in some Western Palearctic locations, but these sightings are not confirmed. Claims of single birds in Italy and Greece have not been proven with clear evidence. A sighting at RSPB Minsmere in 2004 is now believed to have been a Eurasian curlew instead.

In 2007, a report in British Birds magazine mentioned a sighting of a single bird in Albania in 2006 by a team including ornithologists from EuroNatur. The species was officially declared extinct in 2024, with the IUCN updating its listing on 10 October 2025. This study did not consider any sightings after the last confirmed report in Morocco in 1995 to be reliable.