In the spring of 1924, Valentin Ushakov was birdwatching on the marshes near his home town of Tara in south-western Siberia. He was searching for one bird in particular: the slender-billed curlew. Before the Russian revolution he had made regular trips to the marshes and had occasionally seen the curlews. He had even discovered a few nests and collected the eggs. The revolution had interrupted his excursions, but now he was back. The word among ornithologists was that the slender-billed curlew was dying out. But that evening, Ushakov spied several. They flew right past him, making for a small island. He followed, and found 14 nests, all containing eggs.
No one has seen a nest since. All we have is this one egg, collected by Ushakov in 1909 and now preserved at The Manchester Museum. The curlew is almost extinct, and unless conservationists can find where the last remaining birds nest they will have little chance of saving it.
IT WAS getting towards evening on 4 May 1998. On the north-east coast of England, Tim and Ann Cleeves slipped quietly into one of the hides overlooking Druridge Bay. They had come to watch the curlews probing for food around the shore. As they looked out, a small aircraft flew overhead, scaring the birds. Among the rising curlews was one that was smaller and daintier than the rest with an unusually fine, curved bill. The strange bird turned out to be a slender-billed curlew, the rarest bird in Europe.
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In the 19th century, the slender-billed curlew was common. Vast numbers spent the summer somewhere in western Siberia or just across the border in Kazakhstan, where they raised their young, then ate themselves to fatness before heading west to warmer climes for the winter. The migrating curlews stopped at wet places across southern Europe 鈥� a bog in Bulgaria, a lake in Hungary or a brackish lagoon in Albania 鈥� before settling in on marshes and mudflats around the Mediterranean. Europe鈥檚 ornithologists knew what the bird looked like, the sound of its cry and something of its annual migration, but no one knew where its breeding grounds were. Where it went and what it did each summer after flying back over the Urals remained a mystery.
To the people around the Siberian town of Tara, however, the slender-billed curlew was a familiar sight. Hunters shot the birds and sold them at Tara鈥檚 game market. In the early years of the 20th century, local ornithologist Valentin Ushakov decided to investigate their secretive nesting habits. In 1909, he found his first nest and collected his first eggs. He described what he had seen in a hunting journal, and when a translation reached the world outside Russia, ornithologists clamoured for more information.
According to Ushakov, the birds turned up in mid-May and 鈥減robably left in late August鈥�, although no one had seen them go. 鈥淭he nest is made in a little hollow, with a little dried grass,鈥� he reported, and was 鈥渁lmost always in the middle of the marsh on grassy hillocks or small dry islands鈥�. Local hunters had told him they sometimes saw groups of nests, as many as 10 together, but he had never seen any sign of a colony.
By the time Ushakov returned three years later, the curlews had grown scarcer. Villagers told him that the numbers had fallen every year since his last visit. 鈥淚t became clear that the slender-billed curlew was either extremely shy and cautious, or it has changed its breeding area and might even have disappeared from our region,鈥� he wrote in 1912. He found no nests that year. In 1914, he saw two, one brought to him by a hunter and another he found at the same place.
War and revolution put a stop to Ushakov鈥檚 bird-watching trips until 1924. Out on the marshes that May, he noticed some familiar shapes flying towards him. They rushed past, and he followed, hoping they would lead him to some nests. 鈥淚 proceeded to this little isle. When I reached it, curlews began to take off around me and I noticed their nests with eggs. I found 14 nests altogether.鈥� The hunters鈥� stories about colonies of curlews had been true.
That was the last time anyone saw a nesting slender-billed curlew. No one knows what went wrong, but its decline was spectacular. Hunters all along its migration route took a huge toll: the bird was said to be either tamer or more stupid than other waders, always the last to take off when a hunter approached. More recently, changing climate, the draining of wetlands and the spread of intensive agriculture may have added to its troubles. Once its numbers had fallen below a critical level, adult birds must have found it increasingly difficult to find a mate. And if they generally nested in colonies, the shortage of birds might have upset their normal patterns of behaviour.
By the 1960s, the birds were extremely rare. In the 1980s, just a few were seen wintering in Morocco. Today, with no sightings since 1998, ornithologists can do little more than guess at how many are left. 鈥淭he current estimate is fewer than 50 but everyone hopes that is wrong,鈥� says Umberto Gallo-Orsi of Birdlife International. But the English bird offered a glimmer of hope. Its plumage marked it out as a young bird, hatched the previous year. At least one pair of curlews had bred in 1997. But where?
Until conservationists find the slender-billed curlew鈥檚 breeding place there is little they can do to help it. A succession of expeditions to the last known nesting place 鈥� Ushakov鈥檚 marshes 鈥� failed to find a single bird, let alone a nest. But the expeditions may have searched in the wrong places. 鈥淭he habitat around Tara might have been untypical of the places the curlews nested,鈥� says Geoff Hilton of the Royal Society for the Protection of Birds. 鈥淢ost of the birds may have been nesting further north in the tundra or the boreal forest. Or they could have been further south in the steppe.鈥� That extends the search area to a region stretching from the Urals in the west to Mongolia in the east and from the far north of Russia south into Kazakhstan. Where, in so vast an area, do you start to look for a handful of birds?
Hilton believes that the best hope of pinpointing the breeding grounds lies with specimens of curlew skins held in museum collections. Locked in the feathers are chemical signatures that offer clues to where the birds lived and fed when their feathers were growing. Hilton has identified around 200 specimens collected since 1840 and held in museums across Europe. Around half the birds were youngsters, still wearing the plumage that formed while they were in the nesting grounds.
The signatures Hilton is looking for lie in the relative quantities of stable isotopes of elements common in the environment. Carbon, for instance, occurs as the abundant isotope carbon-12 and the rare isotope carbon-13. The proportions of these isotopes vary from place to place and from one ecosystem to another. The ratio of the two carbon isotopes is closely linked to the type of vegetation. With normal hydrogen and its heavy isotope deuterium, the ratio depends on the origin of local rainfall. Crucially, for an ecologist interested in a bird鈥檚 origins, the isotope ratios that characterise a region or a habitat are reflected in the tissues of animals that live there. 鈥淎 feather will contain an isotope signature that reflects the location, habitat and diet of the bird when that feather grew,鈥� says Hilton. Once the feather stops growing, the signature is frozen.
With a tiny sample of feather and a mass spectrometer, Hilton can produce a signature for each long-dead bird. But to locate its birthplace, he also needs a map of the isotope signatures across the region where the slender-billed curlew might have nested. To that end, teams on the ground in Russia and Kazakhstan are collecting feathers from more common waders that follow a similar lifestyle to slender-billed curlews. 鈥淭his should allow us to generate isotopic contour maps of the region,鈥� says Hilton. 鈥淭hen we can place our slender-billed curlews on those maps, to find a 鈥榩lausible range鈥� for the species. The more narrowly defined the plausible range, the more precisely we can direct future expeditions.鈥�
When Ushakov discovered his colony of 14 nests, he was thrilled. 鈥淢any ornithologists would give a lot to observe this picture,鈥� he wrote. He can never have realised just how much.