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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.

The radar

Radar
Photo: Cecilia Nilsson

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

Radar close up
Photo: Cecilia Nilsson

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.

The questions

Flying bird
Photo: Anders Hedenström

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.

Detailed analysis

Radarpanel
Photo: Cecilia Nilsson

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.

The results?

Bird tracks
Bird tracks
We are still in the process of gathering and analyzing data from our radar studies in Falsterbo. In the autumn of 2009 ca 1700 tracks of individual birds where collected, and of these about 600 where tracks of bounding passerines of good enough quality to analyze. In spring 2010, some 1000 tracks where collected, with approximately 400 good quality bounding passerines.
Page Manager:

Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden