Tlw Wilson Journal of Ornithology I24(4):775 782, 2012 
INTRODUCED SPECIES DOMINATE THE DIET OF BREEDING URBAN 
COOPER'S HAWKS IN BRITISH COLUMBIA 
JENNA A. CAVA, 14 ANDREW C. STEWART, 2 AND ROBERT N. ROSENFIELD 3 
ABSTRACT.—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 1 lawks (Accipiter coopcrii ) 
in Victoria. British Columbia, Canada during 1995-20)0. Small 27 g) to medium-size (28-91 g) bird species 
contributed the majority (79-94*7-) 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*7 and 93%, respectively). One native and Luo introduced species provided most (> 85%) prey recorded in all samples 
in which birds were identified to species; American Robin (Turdits migratoriiis). European Starling (Stlimits 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 earlv-season diet (Mar-Apr) was 
comprised of adult birds and subadull 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 16 of 87) on or near the University of Victoria campus where nearly all European rabbit 
(Oryetolagus cuniculus) prey was recorded. Received 28 December 2011. Accepted 4 Ma\ 2012. 
Urbanization is a major force in changes of 
global land-use (Ortega-Alvarez and MacGregor- 
Fors 2011). Urban environments are relatively 
new habitats for Cooper's Hawks ( Accipiter 
cooperii) and other birds of prey (Bird et al. 
19%, Stout et al. 2007, Rosenfield et al. 2009). 
These landscapes vary greatly in size, habitat 
heterogeneity, prey populations, and other eco¬ 
logical factors that potentially affect reproductive 
success of raptors (Stout and Rosenfield 2010). 
Little research has been done on breeding raptors 
in urban settings and fundamental ecological 
understanding of these populations is lacking 
(Stout et al. 2005. Rutz 2008, Stout and Rosen¬ 
field 2010). 
Some of the highest nesting densities and 
reproductive success for Cooper’s Hawks occur 
in cities (Rosenfield et al. 2007b, Mannan el al. 
2008. Stout and Rosenfield 2010). Investigators 
have suggested high nesting densities and repro¬ 
ductive success of urban Cooper’s Hawks could 
he related to abundance and type of avian prey in 
cities (Marzluff et al. 1998, Stout and Rosenfield 
2010). However, there are few reports of the diet 
o! urban Cooper's Hawks. A 2-year investigation 
by Estes and Mannan (2003) in Tucson. Arizona 
appears to be the only published research that 
provides a detailed study of the diet of urban 
'V 174 N .8473 Schneider Drive. Menomonee Falls. WI 
53051, USA. 
: 1921 Doran Road. Cobble Hill, BC VOR IL5. Canada. 
Department of Biology, University of Wisconsin, 
Stevens Point. Wl 54481. USA. 
4 Corresponding author: e-mail: jcava275@uwsp.edu 
breeding Cooper's Hawks. Our objective was to 
document the diet of Cooper's Hawks breeding at 
high nesting densities in Victoria. British Colum¬ 
bia, Canada. 
METHODS 
All data were collected in the city of Victoria, 
British Columbia, Canada during 1995-2010. 
This is a 89-knv city with a human population 
of ~300,000. It has a temperate, coastal climate 
and is comprised of sparsely to heavily wooded 
habitat dominated by tall coniferous trees includ¬ 
ing Douglas-fir (Pseudotsugci menziesii) and 
grand fir (Abies grandis) (Campbell ct al. 1990). 
Nests were found annually by systematic searches 
of the entire city and prey reported represent all 
habitats therein (Stewart et al. 1996), 
Direct Observations.—We recorded 437 inci¬ 
dental direct observations of adult Cooper’s 
Hawks with prey items at 87 nest sites from 
March through August 1995-2010. These obser¬ 
vations consisted of direct observations of prey 
carried by hawks or prey dropped in mist nets by 
captured hawks. Samples from each breeding 
stage (pre-incubation, incubation, nestling, and 
fledgling) for each year were pooled because of 
small sample sizes and because proportions of 
avian prey were similar among stages. We noted 
items as native or introduced to the study area when 
possible. Avian prey items were initially catego¬ 
rized into size classes (SC) following Storer 
(1966), Kennedy and Johnson (1986), and Biele- 
feldt et al. (1992) by known mass and bulk of 
familiar species: SC 1 ^ 27 g and SC 2 = 28-91 g. 
775 
