Smithers 2003 abstract
Smithers, B.L. 2003. Northern goshawk food habits in Minnesota: an analysis using time-lapse recording systems. M.S. Thesis, Texas Tech University. 64 pp.
Time-lapse video recording systems were used to collect food habits information for northern goshawks (Accipiter gentilis) in Minnesota during the 2000, 2001, and 2002 breeding seasons. A total of 4,871 hours of video footage was reviewed, and 652 prey deliveries were recorded, of which 450 (69.0%) were identified to species. Goshawks in the study area preyed on 8 categories of mammals and 31 categories of birds. Overall, mammals comprised 55.1% (n = 359) and birds comprised 33.3% (n = 217) of identified prey items. Red squirrel (Tamiasciuris hudsonicus), eastern chipmunk (Tamias striatus), and snowshoe hare (Lepus americanus) were the dominant mammals identified in the diet, while American crow (Corvus americanus), ruffed grouse (Bonasa umbellus), and diving ducks (Aythya spp.) were the dominant avian prey delivered to nests. Mammals accounted for 61.3% of biomass delivered, and avian prey items accounted for 38.7% of prey biomass. Overall, prey diversity and diet equitability was low, and there was high dietary overlap among nests within the study area. The mean number of prey delivered per nestling per day among nests decreased with brood size (F2,252 = 35.46, P < 0.05). Similarly, biomass delivered per nestling per day among nests decreased with brood size (F2,251 = 3.04, P = 0.049), and biomass delivered per nestling per day varied among nests (F13, 240 = 1.73, P = 0.056). Repeated measures analyses indicated that the number of prey delivered per nestling per day (F2,6 = 9.43, P < 0.05) and biomass delivered per nestling per day (F2,6 = 5.96, P = 0.038) varied with brood size.
Goshawks depredated a variety of mammalian and avian species, but red squirrels and chipmunks were the dominant prey among all nests, accounting for 66% of identified prey and 46% of all prey deliveries. This suggests sciurids are a key breeding season prey species for goshawks in Minnesota. Furthermore, the patterns of prey and biomass delivery rates relevant to brood sizes suggest prey availability may be limiting goshawk reproduction in the WGLR.