Habitatpræference hos Råge Corvus frugilegus om vinteren i et bynært område

An analysis is given of the distribution of Rooks Corvus frugilegus in the winter 1996/97 on different feeding grounds within a 1640 ha area around the southern part of Odense (55º20'N, 10º20'E) in Denmark. The study area was subdivided into 12 different habitat types. Observations of foraging Rooks were made along a 40 km transect during 13 surveys separated by approximately 10 days. The duration of a survey was four and half hours on average. During two of the surveys the ground was covered by a few centimetres of snow.

The area was digitalized in ESRI® ArcView and the area of the 12 habitats computed in ESRI® Avenue. By means of the method described by Neu et al. (1974) the hypothesis of equal preferences was tested. The software application PREFER (ver. 5.1) was used to test the actual order of preference/aversion. Foraging Rooks were recorded in all habitats except "lake/pond". On average, 262 Rooks were observed during a survey, with the highest numbers in January and the first half of February. The birds exhibited a significant preference for
habitats with grass vegetation, including pasture, but also for ploughed fields. Fields with winter crops were the areas most avoided. The article argues that a free view during foraging along with a sufficient food supply determines the distribution of foraging Rooks. It is hypothesised that the urban planning and development of many cities during the past 50 years has made it possible for Rooks to utilize areas not available to them before 1950.