Description of the Short-toed Eagle Circaetus gallicus breeding cycle at two sites in SW Slovenia during the years 2010 and 2011

The Short-toed Eagle Circaetus gallicus is a rare and endangered species in Slovenia, with its breeding population estimated at 9-20 pairs in 2011. Owing to the modest data on its confirmed breeding in Slovenia, the author of the present article decided to search for nests of this raptor as well as to gather as much information as possible on its breeding cycle at two sites in SW Slovenia. In 2010 and 2011 he thus carried out, in the vicinity of Griško polje (UTM VL16) and on the southern margins of the Vipava Valley (UTM VL17), several field visits, arranged according to different parts of the day and of the Short-toed Eagle's breeding season (with a total of 83 observation hours in 2010 and 49 hours in 2011). At both sites, he found one Short-toed Eagle's active nest in each season, in both cases built inside a forest, on a steep slope, at the very top of a flat Austrian Pine Pinus nigra canopy, 10 to 14 m above the ground. At the first site, the Short-toed Eagle pair built a new nest in 2011 in the immediate vicinity of the nest from the previous season, while at the second breeding site a pair used the same nest in 2010 and 2011. The distance between the two active nests, where no other Short-toed Eagle bred with certainty, was 7.7 km, which is comparable with the values on the northern boundary of the species' current continuous distribution in Europe. In 2010, no young were hatched in one nest, while in the other the young was hatched in the last week of June and took wing for the first time between 6 and 9 Sep. In 2011, the young were hatched in the first week of June; they were seen flying for the first time, one between 10 and 14 Aug, and the other between 12 and 16 Aug. In 2010, the Short-toed Eagle's breeding activities took place 2 to 4 weeks later than average in Mediterranean countries, while in 2011 they were comparable to the activities in these particular countries. Possible reasons for this were the warmer spring with distinctly above-average air temperatures in April 2011, smaller amounts of precipitation, and more sunshine. In 2010, the Short-toed Eagles left their nesting area between 3 and 9 Oct, whereas in the ensuing year they left before 25 Sep. Between their first flight and departure from their nesting area in the autumn, the young kept close to the nest and in its vicinity, at a distance of up to 1.5 km. In 2010, the author recorded a total of nine events of the young being fed, the only determined prey species being the Western Whip Snake Hierophis viridiflavus.