The Earth's biodiversity is considered to be facing a crisis at a global level, with many experts believing that species may be going extinct at a rate as high as during the great extinctions recorded in the fossil record. Despite this, it is very hard to determine how many species are going extinct, in part because many species have never been documented, but also because it is generally impossible to tell whether a species is extinct, unless it can be confidently asserted that all populations were being monitored prior to extinction. The best recorded organisms tend to be Vertebrates, and one of the most extensively monitored Vertebrate groups are the Birds, a group which tend to be highly visible, and which are often recorded extensively by non-professional citizen-science groups. Despite this attention, many species of Birds have not been seen for a long time, and this cannot always be taken as evidence that they have become extinct: for instance, the Black-browed Babbler, Malacocincla perspicillata, was rediscovered in 2020 after not being observed in 180 years. The apparent extinction of species can be problematic, causing conservationists to cease efforts to protect a species which is close to extinction; conversely failure to realise that a species has become extinct can lead to efforts being dedicated to preserving it which could otherwise have been directed towards other species which might still be saved.
In a paper published in the journal Ibis on 17 November 2024, Greame Buchanan of the RSPB Centre for Conservation Science, Ben Chapple of the Centre for Biodiversity and Environment Research at University College London, Alex Berryman of BirdLife International, Nicola Crockford of the Royal Society for the Protection of Birds, Justin Jansen of the Naturalis Biodiversity Center, and Alexander Bond of the Bird Group at the Natural History Museum, formally declare the Slender-billed Curlew, Numenius tenuirostris, to be extinct.
The International Union for the Conservation of Nature's Red List of Threatened Species currently lists the Slender-billed Curlew as Critically Endangered, on the assumption that the total population is less than 50 Birds and declining. The species is believed to be restricted to the Palaearctic biogeographical region, breeding in central Asia and migrating to Europe, North Africa, the Middle East, and the Arabian Peninsula. Slender-billed Curlews are thought to breed to the east of the Ural Mountains, in the area around Omsk in southern Russia. Isotope studies of museum specimens suggest that the species may also have bred further south, in northern Kazakhstan, while some eggs assigned to the species, also in museum collections, indicate that the species may also have bred to the west of the Urals. Outside of the breeding season the Birds ranged west as far as Western Europe and the Atlantic coast of North Africa, being known from across the Mediterranean Region, the Middle East, the Arabian Peninsula, and the Pannonian Plains of southeast Central Europe.
Once widespread in Europe, Slender-billed Curlews were last observed in Brittany, France, in February 1968, and in North Yemen in January 1984. A colony, thought to be the last, was known on the Atlantic coast of Morocco in the 1990s, with the last reported sighting in the winter of 1997/8, although a flock of Slender-billed Curlews was photographed in southern Italy in March 1995. No subsequent observations of the species have been made, despite extensive searches across its former range, including the Middle East and Central Asia.
The Slender-billed Curlew was first observed breeding in 1912 by Russian ornithologist Valentin Ushakov, who first noted that the species appeared to be in decline. The possibility that Slender-billed Curlews might be at risk of extinction was first raised in 1943 by German ornithologists Erwin Stresemann and Hermann Grote, but it was not until 1988 that the species was identified as Threatened by the International Union for the Conservation of Nature. The species was listed as Critically Endangered in 1994, following a re-assessment of its status, and an action plan for its recovery was produced in 1996.
Based upon this long absence from its known range, and the extensive, yet unproductive, searched which have been made in the last three decades, combined with the declining number of sightings recorded throughout the twentieth century, Buchanan et al. carried out a statistical analysis of the probability that the species might still exist. Based upon this, they conclude that is most likely that the species became extinct in the 1990s, with only a miniscule possibility that the species might still exist in the 2020s.
If this analysis is correct, then the Slender-billed Curlew is only the third species of Bird known to spend a large part of its annual cycle in the Western Palaearctic to have become extinct since 1500, joining the Great Auk, Pinguinus impennis, last reported in 1844, and the Canarian Oystercatcher, Haematopus meadewaldoi, last observed in 1913.
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It is difficult to directly assess the cause of the extinction of the Slender-billed Curlew, since it is likely that the species finally died out around the time that an action plan for its survival was first drawn up. When that plan was produced, it identified that the species was threatened by habitat loss across its range, and potentially being hunted in some areas as well.
The only records of breeding by the Slender-billed Curlew are those made by Valentin Ushakov in southern Russia in the early twentieth century. It is possibly that the main breeding area for the species was further south, on the steppes of northern Kazakhstan, which were extensively converted to croplands by the Russian Empire and Soviet Union in the nineteenth and twentieth centuries, in the process destroying extensive wetlands, which might have served as breeding grounds for Slender-billed Curlews, however, without further evidence, this is purely speculative.
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