DIRECTION, SPEED, AND COMPOSITION OF NOCTURNAL BIRD MIGRATION IN THE SOUTH OF ISRAEL

ABSTRACT Flight paths of more than 40,000 nocturnal migrants were collected by tracking radars simultaneously at two sites in spring and autumn. Winds were similar in autumn and spring: i.e., typical, rather weak trade winds with northerly directions below about 1500 m above sea level and with southerly or westerly directions higher up. The tracks of the birds were concentrated around 190° (between S and SSW) in autumn and around 5° (nearly N) in spring. Slight differences between the directional distribution of birds above the Negev Highlands and the Arava Valley could be attributed mainly to local winds and topography. Reversed migration occurring in autumn was at the altitudes of the southwesterly winds. Tracks and headings of different wingbeat classes did not differ significantly, except that birds with low wingbeat frequency and passerine-type flight had more westerly directions in autumn and more easterly directions in spring. Mean groundspeed in autumn was nearly 50 km/h, most birds profiting from...