Influence of meteorological conditions on flight altitudes of birds

Understanding the dynamics of the flight altitudes of birds above the landscape has important implications for several applied fields such as civil and military flight safety and bird conservation particularly in relation to wind turbines, power lines and other tall features in the landscape. The flight altitudes of several groups of birds are influenced by meteorological conditions. In addition, they may also be influenced by body structure, flight strategy and behavior (such as foraging, migration or roosting). Birds that rely on various forms of lift for flight or that forage on food sources vertically distributed in the atmospheric boundary layer may be more influenced by meteorological conditions than birds involved in active flight during local movements.

The flight altitudes of several species representing soaring birds, aerial foragers and an intermediate group using flapping and gliding flight were measured in the Netherlands with a fan beam antenna for selection and a pencil beam antenna for tracking of birds. The influence of meteorological conditions on flight altitudes during local movements has been modeled. Factors that influenced flight altitudes included temperature, relative humidity, sea level pressure, cloud cover, boundary layer height, wind speed and lifted index. Flight altitudes of the buzzard (Buteo buteo) a soaring bird of prey and Swifts (Apus apus), which are obligatory aerial foragers, were influenced by conditions reflecting thermal activity. Black headed gulls (Larus ridibundus) were influenced by meteorological conditions although this differed for flapping and soaring flight. Furthermore, meteorological conditions appear to influence the choice of flight strategy in black-headed gulls. Results of this study are being applied to the development of a Bird Avoidance Model aimed at predicting the spatial and temporal distribution of birds in northwest Europe to improve military flight safety.