We used collection of prey remains, direct observations of hawks with prey, and video cameras at two nests to assess frequency of occurrence and biomass of prey species taken by breeding Cooper's Hawks (Accipiter cooperii) in Victoria, British Columbia, Canada during 1995–2010. Small (≤ 27 g) to medium-size (28–91 g) bird species contributed the majority (79–94%) of prey recorded from collection of 3,231 prey remains, 437 direct observations, and 783 video items at 87 nest sites. Avian prey contributed over half of prey biomass recorded in direct observations and video data (67% and 93%, respectively). One native and two introduced species provided most (> 85%) prey recorded in all samples in which birds were identified to species: American Robin (Turdus migratorius), European Starling (Sturnus vulgaris), and House Sparrow (Passer domesticus). Introduced species were an important component of the diet, contributing over half of items identified in all samples. There was a temporal shift in age of prey used: the early-season diet (Mar–Apr) was comprised of adult birds and subadult mammals, while avian young of the year dominated the diet from late May until the end of the breeding season (70–100% of identifiable items). Mammals were inconsequential in terms of frequency and biomass except at nests (6 of 87) on or near the University of Victoria campus where nearly all European rabbit (Oryctolagus cuniculus) prey was recorded.