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Other information on trends over the period 1970-2001, using mainly the same source of data, revealed the following percentage changes: Corncrake Crex crex (+14, increasing after period of severe decline), European Turtle Dove Streptopelia turtur (-77), Common Cuckoo Cuculus canorus (-43), Barn Swallow Hirundo rustica (+11), Yellow Wagtail Motacilla flava (-59), Lesser Whitethroat Sylvia curruca (+2), Greater Whitethroat Sylvia communis (-18), Spotted Flycatcher Muscicapa striata (-82), Red-backed Shrike Lanius collurio (-90) (Gregory et al. 2004). The slightly different figures for some species between the two studies result from the slightly different time periods and possibly the different methods of analysis (see original papers). The massive increase of the Osprey is attributable to recovery from previous persecution. From Gregory et al. (2002).

Other information on trends over the period 1970-2001, using mainly the same source of data, revealed the following percentage changes: Corncrake Crex crex (+14, increasing after period of severe decline), European Turtle Dove Streptopelia turtur (-77), Common Cuckoo Cuculus canorus (-43), Barn Swallow Hirundo rustica (+11), Yellow Wagtail Motacilla flava (-59), Lesser Whitethroat Sylvia curruca (+2), Greater Whitethroat Sylvia communis (-18), Spotted Flycatcher Muscicapa striata (-82), Red-backed Shrike Lanius collurio (-90) (Gregory et al. 2004). The slightly different figures for some species between the two studies result from the slightly different time periods and possibly the different methods of analysis (see original papers). The massive increase of the Osprey is attributable to recovery from previous persecution. From Gregory et al. (2002).

decline differed between species, the Greater Whitethroat suffering a catastrophic crash mainly in one year, and others showing more gradual declines over 10 or more years, with some subsequently recovering somewhat and others not. These differences may reflect differences in wintering areas between species, or in the mechanisms involved, and in some species may be confounded by simultaneous changes in breeding areas. For some species drought might be expected to reduce the food supply only in the year concerned, while for others it might also destroy the shrubby habitat which could take years to recover, or not recover if human activity prevented it. Some European-Afrotropical migrants showed no marked net change over the period considered, while a few showed a substantial rise. Most of the latter winter well south of the Sahel zone, however, and some extend south of the equator to the austral summer.

In general, species that winter in the Sahel zone, or pass through in autumn and spring, showed lower population levels in Britain in 1984, 1985 or 1991 than in any previous year since 1962 (when the Common Bird Census started). They included, besides those just mentioned, the Barn Swallow Hirundo rustica, Grasshopper Warbler Locustella naevia, Eurasian Chiffchaff Phylloscopus collybita and Spotted Flycatcher Muscicapa striata. The Chiffchaff subsequently recovered but the Willow Warbler Phylloscopus trochilus continued to decline (Peach et al. 1995), as did the Spotted Flycatcher (Table 24.5; Peach et al. 1995, 1998). Moreover, annual fluctuations in the numbers of some species followed annual fluctuations in the preceding year's rainfall in the Sahel zone, as shown for the Sedge Warbler Acrocephalus schoenobaenus in Britain and the Netherlands (Figure 24.5, Peach et al. 1991, Foppen et al. 1999). Similarly, in British Swallows, breeding numbers were not correlated with rainfall in their South African wintering areas, but with rainfall in the western Sahel, at its driest during spring migration (Robinson et al. 2003).

Comparisons of count data from different countries have shown that year-to-year changes in numbers are often correlated over large parts of the European

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