A Comparison for Birds of Prey of Ringing Recoveries from Scandinavia against North Sea Oil Records

A Comparison for Birds of Prey of Ringing Recoveries from Scandinavia against North Sea Oil Records

Sources:

Thorpe, A W, (2001), The North Sea Bird Club, 21st Anniversary Report, Aberdeen University.

Toms, M P, & Clark, J A, (1998), Bird Ringing in Britain and Ireland in 1996, Ringing & Migration 19(2) 95-168.

Species	N Sea Oil Rigs in 21 years 1980-2000	Ringed Norway, Sweden, Finland, recovered Britain to 1996	Ringed Britain, recovered Norway, Sweden, Finland to 1996
	Total count over 21 years	Total recoveries	Total recoveries
Honey Buzzard Pernis apivorus	1	1	0
Red Kite Milvus milvus	3	0	0
White-tailed Eagle Haliaeetus albicilla	0	0	0
Marsh Harrier Circus aeruginosus	6	0	0
Hen Harrier Circus cyaneus	5	2	4
Montagu's Harrier Circus pygargus	1	0	0
Goshawk Accipiter gentilis	3	1	0
Sparrowhawk Accipiter nisus	25+ per annum	24	9
Common Buzzard Buteo buteo	9	0	0
Rough-legged Buzzard Buteo lagopus	1	3	0
Golden Eagle Aquila chrysaetos	0	0	0
Osprey Pandion haliaetus	24	20	2
Common Kestrel Falco tinnunculus	Commonest raptor (so 25+ per annum)	45	6
Red-footed Falcon Falco vespertinus	1	0	0
Merlin Falco columbarius	Common but normally fewer than 10 per annum	1	1
Hobby Falco subbuteo	13	1	0
Gyr Falcon Falco rusticolus	2	0	0
Peregrine Falco peregrinus	60 in last ten years	17	0

Note:

The lone Honey Buzzard to date in the North Sea was found exhausted on 23 September 1992 on Saltire (58 deg 25 min N, 00 deg 15 min E, about 200km NE of Fraserburgh, Aberdeenshire). It was taken ashore and registered as permanently disabled but unfortunately it died in March 1993. See North Sea Oil Rig Records for confirmation of the absence of sightings of Honey Buzzards in the North Sea in 2000 when the substantial movement occurred in Britain.

Qualifications:

Not all birds of prey have been identified to the species level in the North Sea, in particular for buzzards where it is stated (p.50 under Buzzard Buteo buteo): "there remain many records of Buzzards not specifically identified" (Thorpe, 2001).
Also some past records from the North Sea are under review, in particular for Goshawk (Thorpe, 2001, p.50),

Classification of Raptors on Potential for Direct North Sea Crossing:

Species with high counts in North Sea (say >=5 per annum) and of ringing recoveries (say >=10 in total) can be assumed to make direct crossings of the North Sea in significant numbers: Common Kestrel, Sparrowhawk, Peregrine.

Species with high counts in North Sea (>=5 per annum) and low numbers of ringing recoveries (<10 in total) can be assumed to disperse widely into the North Sea from Britain but few directly cross from Scandinavia: Merlin. Most Merlins at the North Sea Rigs are indeed thought to originate from Scotland (Thorpe, 2001).
Species with lower but still significant counts in the North Sea (>=1 per annum, <5 per annum) and high numbers of ringing recoveries (>=10 in total) may regularly directly cross the North Sea but also appear to make extensive use of the longer indirect crossing to the south: Osprey.

Species with low counts in the North Sea (say <1 per annum) and low numbers of ringing recoveries (say <10 in total) appear to be scarce direct crossers of the North Sea: Honey Buzzard, Hen Harrier, Goshawk, Rough-legged Buzzard, Hobby. Hobby numbers at the North Sea Rigs have increased in the 1990s following their population increase in Britain.
Species with low counts in the North Sea (<1 per annum) and no ringing recoveries appear to not cross the North Sea at all: Red Kite, Marsh Harrier, Common Buzzard. However, it may be safer to call them very scarce direct crossers.
Species regarded as rare vagrants in the North Sea: Montagu's Harrier, Red Footed Falcon, Gyr Falcon.

Species which do not appear in the North Sea at all: White-tailed Eagle, Golden Eagle.

Conclusion:

Only four species appear to be particularly happy with the direct crossing of the North Sea -- Common Kestrel, Sparrowhawk, Peregrine and Osprey. Another 6 species can only be classified as scarce direct migrants, three as very scarce, three as rare vagrants and two as 'no-shows'. The five species Common Kestrel, Sparrowhawk, Peregrine, Merlin and Osprey, which appear in the highest numbers in the North Sea, are all capable of finding food around the rigs in the form of passerines or fish.
The North Sea is indeed a barrier to broad-winged raptor migrants, other than the Osprey. Ospreys of course are powerful ocean fliers, often fishing over the Atlantic Ocean off West Africa and they make little use of land bridges such as Gibraltar to facilitate their migration. On long sea crossings they can also stop and catch fish using rigs or even floating debris as a base. By contrast the Honey Buzzard only crosses the sea, if absolutely necessary, on migration and, although it can land on rigs or debris, it cannot find food there to replenish its energy levels.