Individual tracks of free flying nocturnal migrants recorded by a military tracking radar (see Bruderer 1997): Bruderer, B. The Study of Bird Migration by Radar Part 1: The Technical Basis*. Naturwissenschaften 84, 1–8 (1997). https://doi.org/10.1007/s001140050338 Description of variables Code site code (C88: Col de la Croix) FNr Track number starting each day at 00:00 with 1 Z mean flight altitude (m above radar) Rg mean flight direction (°) Ra mean heading (°, body axis) Vg mean ground speed (cm/s) Va mean airspeed (cm/s) Vz mean climb rate (cm/s) FieldClass Echo class 1-9 based on wingbeat pattern, see description below description of variable FieldClass Code description 1 wader-type large (continuous wingbeats) 2 wader-type small (continuous wingbeats) 3 passerine-type large (regular phases of wingbeats and pauses => bounding flight) 4 passerine-type small (regular phases of wingbeats and pauses => bounding flight) 5 swift-type (irregular phases of wingbeats and pauses => flap-gliding flight) 6 raptor (visually identified) 7 single bird large (partly visually identified) 8 flock of unidentified birds 9 unknown bird