Occupancy rate and habitat variables influencing nest-box use in the tawny owl (Strix aluco)

Nest-box use by owls was examined in a large urban park northeast of Milano (northern Italy) from 1997 to 2000. Nestbox features and several micro- and macrohabitat variables were compared among the 89 sites which held a nest box for at least two years consecutively. Sites were classified according to the use of the nest box they held: unused, used for roosting and used for breeding. The percentage of used nest-boxes increased significantly over the four years of study, being on average 44%, but only a small fraction (12%) were used for breeding. Nest-box use was higher during winter than during both summer and autumn, suggesting that thermal benefits might affect nest-site selection by tawny owls. Used nest-boxes were located higher on trees and were settled in younger wood patches than unused nest boxes. Tawny owls appear to prefer natural cavities to artificial nests for breeding in our study area, while out of the breeding season nest-boxes are often used as shelters. The preference for nest-boxes higher than 6 m suggest that Tawny owls might select higher nest-boxes as a part of a protection strategy against human disturbance, which is very high in the Park of Monza.