Cava et al. • DIET OF URBAN BREEDING COOPER’S HAWKS 
779 
TABLE 5. Prey species constituting frequency in any of three sampling schemes al Cooper s Hawk nests in 
Victoria, British Columbia, 1995-2010. Total sample size of items identified to species is provided below sampling 
scheme headings. 
Prey species 
Prey remains 
In = 2.8%) 
% Frequency 
Direct observations 
«t = 217) 
Video analysis 
(;t = 155) 
.American Robin 
Turdus migratorius 
34.6 
29.5 
40.0 
European Starling 
Sluntus vulgaris 
28.3 
15.2 
18.7 
House Sparrow 
Passer domesticus 
18.8 
31.8 
34.8 
0 
Varied Thrush 
Ixoreus naevius 
1.1 
0.5 
Pine Siskin 
Spinas pinus 
0.9 
0.5 
0 
Spotted Towhee 
Pipila mandat us 
1.0 
0.5 
0 
House Finch 
Carpodacus mexicanus 
5.6 
2.8 
0 
1 *2 
Northwestern Crow 
Carvus caurinus 
0.4 
0 
1.3 
Chestnut-backed Chickadee 
Poecile rufescens 
0.7 
0.5 
0.6 
Rock Pigeon 
Columba livia 
1.8 
4.1 
0 
Northern Flicker 
Colaptes auratus 
0.6 
0 
0 
Gra\ squirrel 
Sciurus carolinensis 
0.3 
0.5 
0 
1 3 
Black rat 
Ratrus rattus 
0 
0.9 
1.3 
Norway rat 
R. norvegicus 
1.3 
5.1 
2.6 
Eastern cottontail 
Sylvilagus floridanus 
0.8 
1.4 
0 
Deer mouse 
Peromyscus maniculatus 
0.1 
0.5 
0 
European rabbi 1 
Oryctolagus funiculus 
0.6 
4.1 
0 
methodological biases. Our samples of prey 
remains, direct observations, and nest video each 
show that avian species arc the most frequent 
items and provide the majority of biomass in the 
diet of Cooper’s Hawks in Victoria. 
Other recent urban and rural studies have also 
shown birds are the most frequent prey (Estes and 
Mannan 2003: Roth and Lima 2003, 2006) and 
provide the majority of biomass (Estes and 
Mannan 2003), and it is likely that birds are also 
important prey in other cities. The lack of 
mammalian and other Mow agility' prey may be 
due to reduced abundance or availability of such 
prey in the areas at the time of those studies. 
Hawks nesting on the University of Victoria 
campus preyed upon European rabbits that were 
present in large numbers (about IK-20 rabbits/ha 
in non-forested habitats), yet elsewhere in the city 
mammals were recorded infrequently. Bielefeldt 
el al’s (1992) suggestion that much of the 
breeding Cooper’s Hawk diet consists of vulner¬ 
able. inexperienced, and ground-foraging individ¬ 
uals is supported by our results. The three most 
common avian species taken in Victoria (Amer¬ 
ican Robin, House Sparrow', and European 
Starling) would be classified as frequent or 
primarily ground-foraging species by Bielefeldt 
et al. (1992), and inexperienced young ot the year 
were the most commonly recorded prey when 
they become available in the season. Cooper s 
Hawks seem to be opportunistic predators but it is 
unknown whether they target vulnerable prey or 
that prevalence of these items in our samples was 
due to higher attack success rates. 
Roth and Lima (2003) reported introduced bird 
species, especially European Starlings and Rock 
Pigeons (Columba livia), were important prey of 
seven female and one male radio marked 
Cooper’s Hawks wintering in Terre Haute. 
Indiana. They indicated small birds (< 70 g) such 
as House Sparrows were rarely attacked despite 
being numerous in their urban study area; smaller 
bird species in their study area were at low risk ot 
predation from Cooper’s Hawks. Il is possible that 
differences in size class used by Cooper’s Hawks 
between our study and others may reflect disparity 
in size of hawks and prey used. Breeding males 
captured most of the prey documented in our 
study, and males often take smaller prey than 
females (Rosenfield and Bielefeldt 1993). It is 
also possible that smaller, sparrow-sized birds 
have a greater risk of predation from smaller 
Cooper's Hawks in the western half of this hawk's 
North American distribution. Smaller body size of 
breeding Cooper’s Hawks in some western 
populations (including in Victoria) appears to be 
influenced by selective pressures ol size and 
agility of their relatively small avian prey 
