Overall Perspective on Ringing Results
with some comments on the September 2000 movement of raptors
Ian Newton (1979, p.194-196) suggests that, on migration, narrow-winged raptors such as falcons and harriers may move directly over the sea while broad-winged raptors such as eagle, vultures and buteonine hawks "are obliged to make as much of their journey as possible overland, on what is often an indirect route, taking advantage of land bridges or short sea-crossings".
Not all broad-winged raptors avoid the sea: Ospreys are a well-known exception. Conversely some harriers, particularly the heavier Marsh Harrier, may only make long sea crossings infrequently.
It is interesting to look at the ringing data for these raptors, available in reports up to the year 1998 in the Ringing & Migration journal published by the BTO. No foreign-ringed Marsh Harriers from Europe, north of Denmark, had been recorded up to 1998 in the UK. About half of the more northerly ringed Marsh Harriers (Germany, Holland, Denmark, Belgium) had been ringed as pulli abroad and recovered the next summer in Britain (1995 report, 18(2) p.140). There is no evidence that such birds had actually crossed the North Sea in the previous autumn.
Foreign-ringed Common Buzzards are very scarce in the UK. Indeed there is only one up to 1998, from Belgium Feb 94 à Tayside Dec 94 (1995 report, 18(2) p.141). None have therefore been recorded from Scandinavia.
Some people seem to assume that Common Buzzards found in eastern England are Scandinavian but there is no real evidence that this is the case (Lack 1986). Record counts of Common Buzzards in some eastern counties in recent years can be correlated with the highest populations of this species in eastern Britain for 200 years, not with stable populations on the continent. Scandinavian Common Buzzards normally move a few weeks after Honey Buzzards at Falsterbo. For instance for 2000 the peak Honey Buzzard movement at Falsterbo was from late August to mid-September and the peak Common Buzzard movement was from mid- to late-October. (Fågelobsar i Skåne, http://www.skof.se/obs/index.html , click on Rovfågelsträcket, then Se Diagram in turn for Pernis apivorus and Buteo buteo).
Common Buzzard migration from Scandinavia in autumn, as measured at Falsterbo, has been declining in the past two decades (Kjellén & Roos 2000). Increased movement recently in eastern England can therefore not be correlated with the reduced movements out of Scandinavia. Further, movements from Scandinavia in September are mainly of adults with juveniles following later (Kjellén & Roos 2000). Any information on the ages of the Common Buzzards moving with the Honey Buzzards in Britain would obviously be useful.
The simple explanation is that the Marsh Harriers and Common Buzzards in late September 2000 were nearly all UK birds exiting or moving rapidly within the UK after being tempted by the earlier good weather to linger in their natal areas.
Swedish Ospreys clearly do cross Britain (from ringing recoveries) and move on a broad front. However, very few were moving out of Sweden by 20th September (Fågelobsar i Skåne as above, Se Diagram for Pandion haliaetus). There were also very few moving through Denmark at this time ( Movements in Denmark ). In any case, with the flourishing British population, why look for a continental origin for more than a few of the birds? A recent example of a Swedish bird in Britain is noted in the North-East Scotland Bird Report for 1999: the 17th Swedish-ringed bird recovered in the UK was found dead on 27th August having been ringed the same year on 6th July as a chick.
Ringing returns do show that Sparrowhawk, Kestrel, Peregrine and Rough-legged Buzzards regularly visit us from Scandinavia. Were any of these mixed-up in the movements? The Rough-legged Buzzard appears to have special ability (or inclination) to cross the North Sea with a total of four (two birds from Sweden, plus singles from Norway and Denmark) up to 1996 (1996 report, 19(2) p.138). Some though may take the long route via Denmark and Holland rather than attempt a direct crossing.
There are only two recoveries of foreign-ringed Honey Buzzards in the UK -- from Germany in 1973 and Sweden in 1976. The older of these was 04.05.21 years old (1996 report, 19(2) p.137). It would be interesting to have more details of the dates and circumstances. Only one Honey Buzzard has been seen in 21 years of bird recording on North Sea Oil Rigs. This implies that birds very rarely cross the North Sea. See North Sea Oil Rig Records.
No free-flying Scandinavian-ringed White-tailed Eagles Haliaeetus albicilla or Red Kites have been recovered in Britain (1996 report, 19(2) p.137).
The overall conclusion is that broad-winged raptors are scarce migrants across the North Sea.
References:
Lack, P, The Atlas of Wintering Birds in Britain and Ireland, Poyser, 1986.
Newton, I, Population Ecology of Raptors, Poyser, 1979.
See also: A Comparison for Birds of Prey of Ringing Recoveries from Scandinavia against North Sea Oil Records
