Raptor Migration in Europe, Asia and Africa using Satellite Telemetry
Bernd-Ulrich Meyburg & Christiane Meyburg, (1999), The Study of Raptor Migration in the Old World using Satellite Telemetry, in: Adams, N J, & Slotow, R H, (edd), Proc 22 Int Ornithol Congr, Durban: 2992-3006, Johannesburg: BirdLife South Africa. Available as: pdf
Bernd-U Meyburg, Joachim Matthes & Christiane Meyburg, (2002), Satellite-tracked Lesser Spotted Eagle avoids crossing water at the Gulf of Suez, British Birds 95(8) 372-376.
These birds were equipped in Germany, Slovakia, Poland, Hungary, Latvia, Russia, France, Saudi Arabia, Namibia and South Africa.
As was expected, crossing of the sea was avoided by all species except Osprey and Peregrine Falcon.
Two Ospreys crossed the Mediterranean Sea at its widest point. An adult female on migration from Germany left the Italian coast near Genoa flew almost due south and spent the night in south Sardinia. The next morning it proceeded to Tunisia. Its male partner started across the Mediterranean from near the Rhone delta, spending the night on Majorca and flying on to Algeria the next day.
The Steppe, Lesser Spotted and Short-toed Eagles which were tracked flew over typical concentration points like the Bosporus, the Straits of Gibraltar and Bab-el-Mandeb.
The dependence of migration on weather was closely studied in the case of the adult Short-toed Eagle. The distances covered each day reflect a marked dependence on the weather. On sunny days the eagle accomplished on average three times more (311km) than it did on overcast or on rainy days (92km). Indeed, the dependence of migrating raptors on meteorological conditions has long been presumed, on the grounds of their use of thermals, but hitherto there has been little evidence of the daily flight distances depending on weather conditions.
A noteworthy route showing the effort taken to avoid a water crossing was taken by a Lesser Spotted Eagle female in autumn 1997 and 1998 (Meyburg, Matthes & Meyburg, 2002). It flew south to the southern end of Sinai and then moved back north to Suez, involving a 500km detour and an additional 3.5 days of flight, rather than cross the Red Sea to Hurghada.
Water barriers are very significant in raptor migration. Water crossings may save considerable time and energy, but migrants risk being lost because of poor weather or fatigue, and very few species make crossings of more than 25km. The mortality of raptors attempting even short sea crossings is relatively well-documented (Meyburg, Matthes & Meyburg, 2002).
The finding that Osprey and Peregrine Falcon cross the open sea fits in well with other studies.
The behaviour of broad-winged raptors, such as the various eagles, is as expected with a clear avoidance of open-sea crossings of any duration.
Both these findings are consistent with the results of the study on raptors crossing the North Sea reported here .
The evidence that a Short-toed Eagle flew over 3 times further in sunny conditions than in overcast or cloudy ones is very relevant to understanding raptor movements in Britain.
No Honey Buzzard Pernis apivorus or Black Kite Milvus migrans were monitored.