Nesting and roosting habitat and breeding biology of the barn owl (Tyto alba) in the Lower Mainland of British Columbia

Nesting and roosting habitat use and breeding biology of the barn owl (Tyto alba pratincola) in the Lower Mainland of British Columbia were studied over 3 years from 1990-92. A total of 236 sites used by barn owls were located, all but 9 of which were man-made. The majority of the sites (72%) were barns, then silos (11 %) and industrial buildings (4%). Natural nest sites were located in both live trees and snags. It is suggested that barn owls choose man-made sites over natural sites because of the increased thermal cover and increased security from predators. Yearly variations in brood size and the mean number of young fledged per nest were observed, with the lowest values for both recorded in 1991. Poor environmental conditions are thought to be responsible for lowered breeding success in this case. The 3 year mean clutch size, brood size and number of young fledged per nest and their standard deviations were 6.5 (+ 3.5), 3.3 (± 2.0) and 2.6 (±2.1), respectively. Taxidermy data provided information on mortality of adult barn owls. Road kills were found to account for the largest proportion (62.9%) of the carcasses, with starvation (16.7%) and unknown causes (14.6%) making up most of the remainder. Mortality in general was lowest in the summer and highest in the winter. Examination of banding records revealed an average age of 28.1 months at death, with most birds being recovered less than 20 km from their place of banding. Contrary to published hypotheses, no evidence of southward migration could be found. Six adult barn owls were radio-tracked and each was found to have a favoured roost site at which it could be located most of the time. The barn owls roosted at both manmade and natural sites, the choice of which seemed to depend on the preferences of the individual. Several barn owl nestbox programs have been initiated in the Lower Mainland and preliminary results from 2 of the programs show occupancy of the boxes at 31-57% about 2 years after the installation of the boxes. Examination of the history of agriculture in the Lower Mainland reveals that acreage of prime barn owl hunting habitat such as pasture and unimproved pasture are declining. The future of the barn owl in the Lower Mainland depends upon the efficacy of farmland conservation programs such as the Agricultural Land Reserve in preserving farmland from urban development.Science, Faculty ofZoology, Department ofGraduat