FORECASTING FLIGHT ALTITUDES AND SOARING PERFORMANCE OF MIGRATING RAPTORS BY THE ALTITUDINAL PROFILE OF ATMOSPHERIC CONDITIONS

Abstract

Large migratory birds such as raptors, storks or pelicans, predominantly use soaring- gliding flight tactic on their iourney between Eurasia and Africa. In this study we compare forecasts for the upper convective boundary and the strength of thermal convection with the flight characteristics of migrating raptors. To forecast soaring conditions, we measured atmospheric conditions by radiosondes at midnight and applied the numerical convection model ALPTHERM. Raptor migration was studied in southem Israel (Arava Valley) in spring and fall 1992by means of a tracking radar. Maximum flight altitudes per day of raptor migration were correlated with the predicted convective depth; the predicted upper boundary of the convective layer showed good agreement with observed data. Diurnal course of climbing rates in thermal circling agreed with model predictions. Thus, altitudinal distribirtion and soaring performance of migrating raptors are predictable by analyzing the atmospheric structure and may lead to specific applications, for example to prevent bird hazards in countries with high concentrations of diumal soaring migration.