Abstract
In the course of ten nesting seasons from 1996 to 2005 I observed nesting by hobbies in Eastern Slovakia within a territory of 1000 km2 in the Košice Basin. During this ten-year period 218 nestings were recorded. The average population density was two pairs per 100 km2 in the monitored territory. In certain quadrants with better occupation it was from four to seven pairs per 100 km2. The birds nested more frequently on very high tension (VHT) electricity pylons (126 instances) than in trees (92 instances). They prefer the nests of hooded crows (Corvuscorone cornix) (110 cases) and ravens (Corvus corax) (90 cases), and in only 18 cases did they use another nesting solution. When nesting in VHT pylons in the 1980’s they used to make more use of crows’ nests, but at the present time they prefer ravens’ nests to a significant degree.