Wind Tunnel Measurements of Long-Time Flights in Relation to the Energetics and Water Economy of Migrating Birds

Abstract

Statements on the energetics and water economy of flying birds must be based on reliable measurements from long-distance flights (long-time flights) and gas exchange. These measurements can be made in free-flying birds by radiotracking (Butler 1985), by catching exhaled air in bags which are then dropped off (Polus 1985), with double-labelled water (LeFebvre 1964) and finally using wind-tunnel methods (Tucker 1968; Torre-Bueno and Larochelle 1978 and others). The apparent advantages of free flight in natural surroundings are limited by two factors: the technical problems of radio-tracking have not yet been completely solved and one cannot be absolutely sure what the bird really does during its flight (exact flight speed, headwinds, gliding phases, turning flight, pauses etc.). With Polus’s method (1985), one obtains only a single data point. Thus wind-tunnel experiments are indispensible for many problems. We improved the wind-tunnel technology to attain long-time flights ranging from 1–3 h (Nachtigall and Rothe 1978; Rothe and Nachtigall 1987; Nachtigall 1987).