Bird migration strategies in relation to wind and topography
Falsterbo peninsula is a well known migration hot spot where many migrating birds pass each year, especially during the autumn season. We use tracking radar at the Falsterbo peninsula, south Sweden, to track nocturnal migrants. We want to answer questions about how the topography and wind situation affect the passing migrants. The project started in 2009 and will continue for a few seasons.
Our radar is a tracking radar that follows individual birds. It is manually operated and small birds can be tracked at distances up to 30 kilometers and at altitudes between 100 and 5000 meters. The targets are classified by the operator of the radar based on the characteristics of the radar echo and wing beat frequency analysis. Species are very difficult to distinguish with the radar, but some special flight behaviors are identifiable, such as the bounding flight used by many passerines
Position, height and speed
When the radar is locked on to a target it records the birds’ exact position, height and speed continually. Individual birds are usually tracked for between 1 to 10 minutes as they pass the peninsula and a good night up to a hundred birds can be tracked.
One important question regards how winds and the surrounding topography affect the birds. Wind speeds in the same range as bird air speeds are not uncommon, making the difference between tail and head winds very important. Topography might affect a migrating bird in several ways; there is for instance rather conflicting evidence on whether migrating birds tend to follow shorelines or not on their journeys.
The radar data will allow us to analyze the passing migrants’ speed in detail, altitude and direction in relation to the topography of the peninsula and the wind situation at each tracking. We will, among other things, be able to see if the birds follow the shoreline or not and if they will compensate for wind displacement or not.