Population trends in Swedish raptors demonstrated by migration counts at Falsterbo, Sweden 1942-97
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The autumn migration of raptors at Falsterbo, Sweden has been studied since the early 1940s, and from 1973 standardized counts were made. Here we present data for 15 species over a 39-year period from 1942-97. These are discussed in the context of available information on population trends in Sweden and neighbouring countries. Although annual numbers and concentration rate vary considerably between species, population changes are very well reflected in the migration figures from Falsterbo. Most raptors showed stable populations at a fairly high level during the 1940s, hilt a marked decline was already obvious in White-tailed Eagle Haliaeetus albicilla and Peregrine Falcon Falco peregrinus. During the 1950s and 1960s, a more or less steep decline occurred in most species. Four species started to increase during the 1960s, but the real change came during the 1970s. At that time, decreased human persecution and a reduction ill the effects from pesticides resulted ill a general increase in Scandinavian raptors, with only Honey Buzzard Pernis apivorus continuing to decrease. The increases continued during the 1980s, but in the 1990s many raptors seem to have reached stable numbers or to have started to decline again. Two species, Marsh Harrier Circus aeruginosus and Montagu's Harrier C. pygargus show a positive trend through the study period. Numbers of Northern Harrier Circus cyaneus, Rough-legged Buzzard Buteo lagopus and Eurasian Kestrel Falco tinnunculus stabilized during Me 1980s and show a clear decline since then, most probably due to a general lack of rodent peaks in Northern Scandinavia since 1982. Most species of raptors scent to he doing reasonably well at the moment, brit a continuous decline in Honey Blizzard and Common Buzzard Buteo buteo is disturbing, and is possibly due to declining proportions of old deciduous forest and grazed meadows in Scandinavia. Since a general census programme of birds of prey does not exist in Sweden, the migration counts at Falsterbo is the best general method of monitoring population changes.