title: The use of low-level jets by migrating birds.
abstract: Birds flying at high altitudes have occasionally been observed above mountain areas and the open sea. For the first time the regular occurrence of migrating birds flying within a low-level jet at heights of 5000 to almost 9000 m asl. have now been verified by radar above the Negev desert in southern Israel. Tracks of rather large birds with wing-beat frequencies of 5-6 Hz were measured to have horizontal flight speeds up to 50 m/s. Visual observations, seasonal occurrence, and wing-beat frequencies allowed to associate them with small species of the order Ciconiiformes (mainly Ardeidae) and possibly with members of the Laro-Limicolae group. These wading birds seem prone to continuing nocturnal migration into daytime under favorable conditions and to make use of high wind speeds at sometimes extreme altitudes.
authors.affiliation: Swiss Ornithological Institute, CH-6204 Sempach, Switzerland. liechtif@orninst.ch
authors.forename: F
authors.initials: F
authors.lastname: Liechti
authors.forename: E
authors.initials: E
authors.lastname: Schaller
mesh_terms: D000531:Altitude; D000818:Animals; D001717:Birds / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D012621:Seasons; D014919:Wind