Factors affecting the flight altitude of migrating waterbirds in Western Estonia

We studied the effects of weather conditions, temporal factors and distance to coast on the flight altitude of migrating waterbirds in Western Estonia. We used a laser range finder and marine surveillance radar to measure flight altitudes, and identified significant effects on avian flight altitude by several weather components, particularly wind conditions, visibility and cloud covet Wind components played a particularly significant role. Tailwinds were generally associated with elevated flight altitude, and reductions in flight altitude were usually associated with high wind speed, possibly because of enhanced energetic costs or risk of being blown off course. Behavioural and physical adaptations to the environment also contributed to specific flight-altitude selection. The results provide new insights into factors determining flight altitude and useful information to support environmental impact assessments.