Migration in the Mediterranean Area

Abstract

SUMMARY. The enormous proportion of migrants that must pass undetected is stressed both on statistical grounds and on certain features of the records. There is no evidence for any important concentration of migrants on the short crossings, by the Straits of Gibraltar, Sicily or the Bosphorus, except for soaring birds at the first and last of these. These birds migrate at the Bosphorus using thermals, but only up to about 14.00 (not, as at Suez, also during the afternoon); while at the Straits of Gibraltar they migrate against winds, often strong. Numerous species cross regularly the widest part of the Mediterranean, between 16′ and 20′ E., over the Ionian Sea, where the north‐south distances are 430–800 miles. There is less evidence for crossing of the other widest stretch, France‐Algeria, 430 miles. The fact that the longest crossings are freely used and that most species do not concentrate on the shortest crossings indicates general broad‐front movement irrespective of obstacles. Occurrences of groups and species are summarized and some comparisons are made. Points of interest include:— Harriers are more often seen at sea than other big raptors. The western cranes appear to concentrate on short crossings much more than the eastern do. The movements of Quail and Turtle Doves are of special interest. More Swallows are seen, both at sea and coasting, than any other birds, and many times more than House‐martins. Common Redstarts and Robins have been recorded at sea surprisingly often, especially by comparison with the Sylviidae. Anatidae and Limicolae are almost unknown at sea. The leading published references to migration in the countries in the Mediterranean area are summarized in an appendix.

Migration Across the Mediterranean Observed by Radar

“…T h e scale of migration across the whole area seems to be very much as predicted by Moreau (1953) and Lack (1961) but the migration season extends over a rather longer period than has generally been accepted. It was well under way by 18 August and still strong on 24 October in autumn, and continuing at least as late as 13 May in spring.…”

“…The coastline at Cape St. Vincent, however, turns sharply east, and no longer acts as a leading line. The southwesterly urge appears to become dominant again (as shown at P) and, as Moreau (1953) points out, Steinfatt observed a movement, consisting mainly of Swallows, setting off from Tarifa in the morning of 6 October 1933 heading S.W. This direction is not as suicidal as it would appear from Map 1; the birds would strike land some 600 miles away in the Canary Islands.…”

“…AUTUMN-MAP 9 I paid special attention to this area on the few occasions I was able to cover it with a radar set. As Moreau (1953Moreau ( , 1961 points out, this is the longest sea-crossing in the Mediterranean, and yet there is no shortage of visible migrants reported from sea in this area. M. C. Powys Maurice and I together recorded the observations referred to in Moreau (1953 : 341) and in September-October 1962, October 1963, February and September 1964, and May 1965 I have crossed the Ionian Sea and always recorded some migrants, the commonest being j u v u wagtails.…”

Environmental and geographical constraints on common swift and barn swallow spring arrival patterns throughout the Iberian Peninsula

“…1) seem to act as effective barriers to the eastward migration of barn swallows. A direct crossing of the sea from North Africa to the south‐eastern Spanish Mediterranean coast does not appear to be undertaken by many individuals (Bernis, 1971, but see Glainville & Walker, 1962): the Gibraltar area provides the main access to Europe for this species (Moreau, 1953; Bernis, 1962). As a consequence, the colonization of south‐eastern Iberia is delayed, despite its proximity to Gibraltar and early onset of conditions suitable for breeding.…”

Migration From Morocco Into Southwest Spain in Relation to Weather

“…Such large-scale diversion of migrants by a coastline is probably unusual a, Drury 1960, and is especially surprising since the sea-crossing involved is only two hundred miles at the most, and the same species are known to make much longer seacrossings over the Mediterranean (Moreau 1953 and1961). A tendency to follow this coast would, however, reduce the risk of excessive drift over the Atlantic-which is obviously much more dangerous than lateral drift during a crossing of the land-locked Mediterranean.…”