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Threats and limiting factors
* Habitat
loss
Due to the lack of knowledge concerning the location of the breeding grounds, it is not
possible to assess the scale of threat posed by their modification/loss. In general the taiga
has been little modified, the forest-steppe partly cultivated (but with many wetlands
remaining), and much of the steppe severely modified by intensive agriculture. The
importance of this factor could thus range from low to high, depending on which habitat
is used for nesting.
Much of the passage route has been greatly modified by man,
for example the Aral Sea
area and the steppe areas of central and eastern Europe. There has also been a general
loss of wetlands throughout the western Palearctic. The loss of traditional stopover sites
may have had serious effects on the Slender-billed Curlew, but, as noted above, it can use
a range of passage habitats and yet has still suffered a much greater decline than other
waders crossing the same region.
Parts of the winter quarters (e.g. the Rharb plain of north-west Morocco) have been
greatly affected by man, with large-scale drainage of wetlands. In Tunisia also,
temporary freshwater marshes (e.g. Kairouan) have been seriously damaged by the
construction of dams for flood control and the provision of water supplies. Elsewhere in
North Africa, however, other types of wetland have been less affected, such as coastal
sites and inland sebkhets/chotts (temporary brackish wetlands, e.g. those near
Constantine in Algeria). The situation is hard to assess while Merja Zerga remains the
only known current regular wintering site for the species. In the Middle East, the marshes
of Iraq are potentially a very important wintering site, but are rapidly being destroyed.
The area of the central (Qurnah) marshes had been reduced by 1991/92 to 67% of its
1984/85 area, while the area of permanent marshes overall had been reduced to 40% of
the 1984/85 area (from 1,133,000 ha to 457,000 ha). If drainage plans proceed as at
present, the marshes will probably be lost in 10–20 years (Maltby 1994).
Importance:
low-high (breeding areas)
medium-high (passage and wintering areas)
* Hunting
In the early part of the twentieth century, across much of Europe, hunting of waders took
place on a large scale (principally for food), with curlews (as the largest waders) being a
favoured quarry. Significant numbers of Slender-billed Curlew specimens, notably from
Hungary and Italy, date from this time, the birds often being from markets (Gretton
1991). Because the Slender-billed Curlew is often tamer than its congeners (Gretton
1991), it could have suffered very heavily at this time. Indeed there is considerable
evidence that hunting may have been the key cause of its decline, with habitat loss an
important secondary factor – though it is hard to imagine habitat loss affecting this one
species more than any other European wader. The selective threat posed by hunting is
clear: curlews were the prime wader targets for food, and Slender-billed Curlews
(according to much evidence) were the tamest curlew. It would be difficult, perhaps
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impossible, to prove absolutely that hunting was the key factor some 60–100 years after
the main period of decline, but the available evidence points in this direction.
At least up to the 1970s there was also strong hunting pressure in parts of North Africa.
At present the threat is generally less, but between 1962 and 1987 17 Slender-billed
Curlews are known to have been shot (13 of these in Italy and former Yugoslavia). With
the world population being so low, this number is highly significant; the loss of even a
single further bird to hunting is unacceptable.
Importance:
medium (but historically high)
*
Breakdown of social behaviour patterns
This is very much a secondary factor, not responsible for the original decline, but likely
to be important in keeping numbers low following the main decline (i.e. during the last
30–50 years). Early records often referred to large flocks of the species on migration and
in winter, and it is possible that the experience of older birds was important in guiding
such flocks. As Slender-billed Curlew numbers fell, individuals would be more likely to
join flocks of other species, notably Eurasian Curlew. The chances of Slender-billed
Curlews meeting each other on the breeding grounds would become increasingly low, as
was graphically described for the Eskimo Curlew by Bodsworth (1954). Without drastic
(and probably unfeasible) intervention, there is little that can be done to ameliorate these
effects.
Importance:
medium-high (following initial decline)
* Other
factors
Many other possible causes of the decline have been considered (Gretton 1991), but very
few are thought plausible.
Two factors, affecting parts of Kazakhstan potentially used by
the species, are highly speculative but warrant a mention, although it is difficult to obtain
precise information on either. The level of use of agricultural chemicals in the Aral Sea
area (since the 1950s) has caused widespread concern, and has been held responsible for
widespread human illness and high levels of child mortality. The lack of water in the area
would serve to concentrate such chemicals still further, and could contaminate Slender-
billed Curlews via their food, or directly in drinking water.
There are (unconfirmed) reports of nesting Slender-billed Curlews from Ust-
Kamenogorsk and Semipalatinsk (Gavrin et al. 1962) in the 1920s and 1930s. The main
nuclear testing ground of the former U.S.S.R. is just west of Semipalatinsk, and was used
until very recently. In earlier years atmospheric tests were conducted here, presumably
causing major contamination. Summer records of the species are also known from the
Chelyabinsk region (Gavrin et al. 1962), and in recent years very high levels of
radioactivity have been found in the environment near Chelyabinsk–40 (E. Nowak
verbally). At present we do not have enough information to assess whether such factors
could have affected the Slender-billed Curlew, but the possibility cannot be entirely ruled
out.
Importance:
unknown
Conservation status and recent conservation measures
* International