Náttúrufræðingurinn

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Náttúrufræðingurinn - 1992, Qupperneq 73

Náttúrufræðingurinn - 1992, Qupperneq 73
(June-July) and one from winter (De- cember) (Fig. 6). Geographical distri- bution of the records is shown in Fig. 7. Ten specimens in the IMNH, col- lected during autumn, include two adult males and eight immatures (six females and two males). Four speci- mens from spring are immatures (two males and two females). These va- grants probably originate from North- and West-Europe, as indicated by three recoveries of Kestrels banded as nestlings (one from the Netherlands and two from Sweden). 12. Red-footed Falcon (Falco vespertin- us). Three records: adult male July 1980, adult male April 1981, and male April 1985. 13. Hobby (Falco subbuteo). Seven rec- ords, all from spring (three, April) and summer (four, June-July). 14. Peregrine Falcon (Falco peregrinus). Four records: adult male July 1961, immature female October 1985, one October 1986, and immature female December 1988. The first two birds belong to the nearctic race F.p. tun- drius. Most of these raptors strayed to Iceland during the migration period of the species in question. Raptors can be divided into two groups according to their mode of travel during migration (Newton 1979). The first group “soarers” is represented by relatively large raptors with long broad and rounded wings, e.g. eagles, buzzards and vultures. These birds depend heavily on thermal updrafts on their journeys, tliey travel mostly over land, and if they have to cross oceans they use the shortest possible route, e.g. narrow straits. The second group “flappers” is composed of small to medium size raptors with long and narrow wings. These birds are not de- pendent on thermal updrafts and travel readily over open water. The accipiters form an intermediate group, they regular- ly use thermal updrafts but also travel readily over open water. “Flappers” are more common as vagrants in Iceland (9 species, 92 records) than “soarers” (5 spe- cies, 18 records). This probably reflects the reluctance of “soarers” to travel over open water. The ratio of these two groups, “soarers” versus “flappers”, is more equal in the avifaunas where Ice- landic raptors originate, Europe and North-America. Before 1940 only two of these 14 species had been recorded in Iceland (Kestrel one record, Osprey two records). Since 1940 there has been a drastic increase (Fig. 8). This increase is believed to be caused primarily by increased number of observ- ers. 215
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