Some aspects of the occurrence and behaviour of the crane Grus grus in Poland in light of pre-investment wind-farm monitoring

Abstract Ornithological pre-investment monitoring at planned wind farm sites is a standard and obligatory procedure in Poland and other EU countries. Pre-investment wind farm monitoring has a very important ‘side effect’ to its main goal (the safety of bird populations), namely the collection of valuable avifaunistic data from many localities that most probably would never be studied if not for the obligation to prepare environmental reports when wind energy investments are planned. The main aim of this paper is to show what we can learn from obligatory pre-investment monitoring when the standard field monitoring procedure and unified evaluation methodology are used. As an example the Common Crane Grus grus was selected, as a bird listed in Annex 1 of Directive 2009/147/EC and easy to identify and count. The data were collected at 155 controlled monitoring sites all over Poland, but mainly along the Baltic coast and in the Masurian Lake District. The methodology of the data collection and evaluation of results was strictly according to a paper by Busse (2013). The presentation of the results includes the numerical distribution of cranes in all seasons and some details of their behaviour - observations of birds on the ground and those using the air space: below the future rotor swept area of the wind turbines, at the rotor swept height, and flying above it. The estimated collision rates vary depending on the area, season and local heights of movements. It was concluded that such an evaluation of data already collected could be helpful in evaluating a particular site in comparison with other, previously studied localities.