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Bird migration in Italy
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Radar study of bird migration over a planned power line location in Calabria, Southern Italy

honey buzzard
radar setup
radar image

Terna SpA, the main administrator of the Italian electric grid, is planning to develop a new 380 kV power line in Calabria, Southern Italy. In Spring 2010, Bureau Waardenburg carried out a two-week radar study to quantify the flight direction and altitude of migrating birds through the corridor of the planned power line. The study site was located near the Messina Strait within the Important Bird Area Costa Viola.

Diurnal passage of Honey Buzzards

During daytime the study focussed on the diurnal migration of Honey Buzzards, for which the spatial and temporal patterns through the corridor were mapped with aid of the radar. These patterns were strongly linked to weather conditions (wind force and direction, presence/absence of fog). Good numbers of Honey Buzzards migrating through the corridor were mostly observed during days with good visibility. On such days, those birds that flew at low altitudes were observed to cross a nearby existing power line, seemingly without any effort. Using the radar we were able to accurately quantify flight altitudes and directions of passing birds and to show that during periods of fog there was hardly any bird migration through the corridor.

Nocturnal migration

During the night many 10,000s of birds were seen by radar to migrate over the corridor. The majority of these nocturnal migrants crossed the corridor many hundreds of meters or more above ground level. Interestingly, the temporal pattern showed several peaks in intensity. Most likely, this was due to take-off locations at successively increasing distance from the observation location, possibly including the southern tip of Italy, Sicily and even Tunisia respectively; which is in accordance with a guided broad-front-migration.

Using radar in migration studies

Using radar made it possible to make a more complete assessment of the numbers, direction and altitude of migrating birds than would have been possible with traditional methods only. Raptors migrating at higher altitudes, that would have been missed otherwise, were regularly picked up by the radar. During daytime, the radar recorded many high flying birds (probably swallows and swifts), which were not visible to the observers. Without radar it would have been very difficult to monitor bird migration during the night and in conditions with dense fog. Therefore, it is recommended to more often use radar in migration studies, especially when details on flight altitude and flight routes are needed for impact assessments.