Migratory; almost entirely a summer visitor to Europe. Winters mainly wooded country in west and central regions of equatorial Africa, from Guinea and Liberia east to Central African Republic and Zaïre; also in much smaller numbers in eastern and southern Africa as far as Natal and Angola. Seldom identified Ethiopia, and Moreau disbelieved report of wintering in numbers in Sudan. Backhurst et al. considered it a scarce migrant in Kenya and Tanzania, mostly seen in spring but also occasionally summering (June–August). Brooke and Irwin reported specimens from Rhodesia, Malawi, and Transvaal, and concluded it is a scarce but regular migrant to whole of south-east Africa. Only exceptionally recorded Cape Province. Birds ringed central Europe and Fenno-Scandia recovered in winter Guinea to Zaïre (emphasizing south to south-west autumn migration), but one East German bird also found Ethiopia.
Departures from breeding grounds mainly mid-August to early September, with adults generally leaving by end August. Most gone from central Europe by late September to early October, though a few (probably juveniles) linger into late October or even November; December–March records in Europe quite exceptional and most require confirmation. Begins returning to central Europe from mid-April (earlier records probably include cases of confusion with Buzzard Buteo buteo), though majority return in second half May, or late May to early June in north Europe; birds moving second half June and early July may be non-breeders.
Although relying mainly on soaring flight on migration, capable of sustained flapping flight over large water crossings; thus less restricted to narrow sea-crossings than other large raptors. Nevertheless, heavy concentrations occur at such points. Scandinavian population leaves via Falsterbo and adjacent parts of Swedish coast, returning over north Denmark. At Falsterbo, peak autumn passage late August to mid-September; rarely over 10 000 per autumn in recent years, but c. 22 000 in 1955. These move on fairly narrow front over south Denmark and east Holstein before fanning out over West Germany. With easterly winds, may pass over East Frisian Islands and Netherlands, sometimes in striking numbers
Ringing recoveries indicate west European populations from as far east as Sweden and central Europe use Straits of Gibraltar route, where main autumn passage late August to mid-September; 117 175 counted crossing there in autumn 1972, with peak counts 13 707 on 5 September and 11 529 on 8 September. In spring, majority cross Straits late April to late May; median passage date 11 May ±6 days. Considerable numbers also cross central Mediterranean via Sicilian Channel; large numbers reported Malta, Sicily, and especially Cap Bon (Tunisia), where c. 8100 recorded, 2–18 May 1975. Timing of spring passage as at Straits of Gibraltar, but autumn peak somewhat later (mid to late September). Recoveries indicate that populations involved originate Sweden, Finland, and central Europe.
East European populations (limits uncertain) concentrate on passage over Bosporus and Sea of Marmara; main movement mid-August to mid-September. In counts 1966–75, maxima 25 751 in 1971 and 23 850 in 1972, with largest numbers last week August. Limited spring observations indicate main passage in May. Considerable confusion between Pernis and B. buteo at Bosporus in past, and observations of large numbers of Pernis in late March and early April and between mid-September and early October, when few or no Buteo reported, seem erroneous; these peak passage times of B. buteo, when Pernis now known to be rare or uncommon. Autumn totals at Bosporus well below those from Straits of Gibraltar and eastern Black Sea (see below), but some evidence that unknown numbers cross directly over Sea of Marmara, often in company with White Storks Ciconia ciconia, and this movement may be considerable.
Migrants from west USSR not using Bosporus route pass around eastern end of Black Sea, where 137 622 counted at Arhavi and Borçka 18 August–10 October 1976 (peak counts 19 743 on 31 August and 37 204 on 4 September). The most easterly populations in west Palearctic may migrate through Caucasus or around east side of Caspian; but not recorded in numbers on passage anywhere in Iran. To west, catchment area for Caucasus route may extend as far as Finland, as now known in B. buteo.
Further south, large concentrations occur Gulf of Iskenderun, where 15 971 over Belen 13 August–23 September 1976 (passage still continuing on latter date), most 25 August–13 September. Also considerable passage in autumn over Cyprus, though not in spring, so some clearly cross over as well as pass around eastern Mediterranean. Lebanon observations made too late in season to record main southward passage of Pernis, but 5155 counted at Harissa, 15–21 September 1968. Great majority passing through Middle East believed to enter or leave Africa via Sinai and Gulf of Suez though confirmation still required. During extensive observations in spring 1977, 226 060 recorded at Elat (Israel), mostly late April to mid-May; autumn observations from Elat, however, still fragmentary.
Although concentrations at narrow sea-crossings well-documented, passage on wider fronts recorded Mediterranean and over western Red Sea, although probably on much smaller scale. Since rare in Iraq and Saudi Arabia and East Africa, likely that little if any passage east of western Red Sea or head of Persian Gulf.
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