Irruptive movements from deserts to neighbouring areas

Normally, desert species are able to remain within their regular range, in the wettest years penetrating deep into the driest areas, but at times of widespread drought, they may move out into neighbouring less arid habitats. This is strikingly illustrated in Australia, as mentioned above, by the periodic outward movement of many interior desert species to the less arid edges of the continent, and in Eurasia by the westward movements of Rose-coloured Starlings Sturnus roseus, Pallas's Sandgrouse Syrrhaptes paradoxus and others from the steppes into western Europe.

In their regular range, Rose-coloured Starlings may settle in thousands in suitable localities, breed and then move on. They feed their young mainly on grasshoppers and locusts, and seldom occur in abundance in the same localities in successive years. Their irruptions outside the usual range occur in spring and early summer, apparently in years when birds return from winter quarters in the Indian subcontinent to find their food supply has failed over wide areas (Schenk 1934). Big irruptions to western Europe occurred in 1853, 1907-1909, 1925, 1932 and 1948, but subsequently they became less frequent and extended less far, only stragglers reaching western Europe (Cramp & Perrins 1994). However, a major movement into Europe occurred in summer 2002, with birds reaching as far as Iceland and Britain. In this year, many thousands of pairs bred outside the usual range, with an estimated 14 000 pairs in Romania, 2000 pairs in Bulgaria and 10 000 non-breeding birds in Hungary (Fraser & Rogers 2004). Nesting at various places in Bulgaria coincided with an invasion of locusts (Davies & Sharrock 2000). Irregular occurrences have long been the norm in Europe. In 1875, 6000-7000 pairs settled to breed in holes in the ramparts of the castle of Villafranca di Verona in northern Italy, then for the next 33 years not a single Rose-coloured Starling was recorded in that country (Voous 1960). Ring recoveries are scarce, but one bird ringed during an invasion in Hungary in June was recovered the next April in a wintering area some 4800 km to the east in Pakistan (Ali & Ripley 1978).

The irruptions of Pallas's Sandgrouse Syrrhaptes paradoxus, which occurred from the steppes of Turkestan and Kazakhstan into western Europe in the springsummers of 1859, 1863, 1872, 1876, 1888, 1891, 1899 and 1908 (with small numbers in some of the intervening years and subsequently) were attributed to seed shortage (mainly of the chenopod Agriophyllum globicum) resulting from prolonged drought. Again, after each of these irruptions there were occasional breeding records, some from as far west as Britain. Irruptions into eastern Asia occurred in different years, indicating that regional factors affected different segments of the population. No substantial emigrations are known to have occurred subsequently, possibly because populations have declined following degradation of nesting habitat.

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