Breeding biology of the Long-legged Buzzard Buteo rufinus in SE Bulgaria, nesting also in quarries

Abstract

Long-legged Buzzard Buteo rufinus breeding numbers have not undergone any significant changes in four gorges in SE Bulgaria during the time period 1994-2007. Between 12 and 16 pairs have nested there, which makes one pair per 0.8 - 2.8 km gorge length, with minimum 0.9 km distance between neighbouring nests. In the absence of natural rocks the birds prefer rock quarries to trees. They build their nests on massive rocks (min 15 m length; min 10 m height), predominantly with southern and western exposition (78 %, n = 32). Nests are usually located on rock terraces, without any prominent shelter (87 %, n = 21). The nests vary between 0.5 -1.1 m (mean 0.71, sd 0.18) in diameter and 0.15 - 0.25 m (mean 0.20, sd 0.04) in height (n = 21 nests on rocks). The clutch size has been 2 - 3 eggs (1 - 4; n = 12 nests) and the brood size has ranged between 1 - 3 young, mostly 2 (50 %, n = 16 nests). The pairs nesting in the quarries feed mainly on small and average-sized mammals and lizards from the open areas, the voles Microtus spp. and European souslik Spermophilus citellus constituting 41 % of the prey. No significant changes have been observed in their diet throughout years, but differences between different nests are significant (χ²_[32] = 67.58, P < 0.001). In five locations they bred jointly with the Eagle Owl Bubo bubo, with a distance of 60 - 650 m from their nests. The Eagle Owl seems not to challenge the breeding of the Long-legged Buzzard in quarries and natural rocks.