Winter census of the water rail Rallus aquaticus in Slovenia

The data on the winter distribution of Water rails Rallus aquaticus and their abundance are poor. By counting them in selected sections of Slovene waters, the study aims to determine the species' densities and to estimate the size of the wintering population. The census was carried out in the winters 1998-1999, 1999-2000 and 2000-2001 at the Hajdina spring waters in Ptuj, and in the winters 1998-1999 and 2000-2001 elsewhere in Slovenia as well. Water rails were counted in the afternoon hours using playback method. At the Hajdina spring waters, a high linear density of 6.4~c0.2/km was established during the three winters. The numbers of the wintering water rails at the water springs and their distribution between separate count sections were very similar during the stated winters. Their average linear density at the courses elsewhere in Slovenia reached 1.7~c1.4/ km in the winter 1999-2000 and 2.6~c2.0/km in the winter 2000-2001. High densities were recorded only at shorter sections. The length of watercourse suitable for this bird is around 1320 km in Slovenia. The size of the bird's wintering population in Slovenia is estimated at 2300~c460 - 3430~c510 individuals. Water rails were not counted on standing waters in the interior of the country, even if not frozen over. During the census, the highest densities were established on slow flowing rivers with lush vegetation on their banks, particularly in the parts overgrown with reed Phragmites australis, where some local densities reached even 2 ind./ ha or 5-6 ind./km of the watercourse.