On the Breeding Biology of Northern Saw-whet Owls (Aegolius acadicus)

Abstract

Abstract We monitored 37 Northern Saw-whet Owl (Aegolius acadicus) nesting attempts at the Boardman Tree Farm (BTF) in north-central Oregon from 2012 to 2015. Nests were initiated from early March to late June and contained an average of 5.7 eggs. Twenty-nine (78%) of the nesting attempts were successful and produced an average of 4.2 fledglings per successful attempt. One male paired with two females and produced 6 fledglings out of 10 eggs. We captured 59 unique nesting adults; 61% of the males (17 of 28) and 58% of the females (18 of 31) were second-year (SY) birds. We captured both adults at 30 nests: both parents were SYs at eight nests, both were after-second-year (ASY) at five nests, the female was SY and the male ASY at eight nests, and the male was SY and the female ASY at nine nests. Considering clutch size and number of young fledged, we found no evidence that pairs composed of SY parents reproduced less successfully than those composed of ASY parents. Sample sizes were small, but neither mean ...