Home Range and Habitat Use of Cooper's Hawks in Urban and Natural Areas
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
SPECIAL TOPIC B
Home Range and Habitat Use of Cooper’s Hawks
in Urban and Natural Areas
Sophia N. Chiang, Peter H. Bloom, Anne M. Bartuszevige,
and Scott E. Thomas
Abstract. During 2001, we used radiotelemetry than expected, whereas Cooper’s Hawks nesting
to measure home range and habitat use of adult in urban areas used parks/ornamental plantings
male Cooper’s Hawks (Accipiter cooperii) in urban and commercial/industrial areas more often than
and natural areas in Orange County, California, expected. Urban-nesting Cooper’s Hawks suc-
USA. Breeding (n ⫽ 8) and non-breeding (n ⫽ 5) cessfully fledged an average of 3.75 ⫾ 0.5 young
season home ranges and core areas were calcu- per nesting attempt, whereas natural-nesting
lated via CALHOME using 95% and 50% adaptive Cooper’s Hawks fledged an average of 1.5 ⫾ 1.9
kernel methods, respectively. We used a G-test of young per nesting attempt. Our results contribute
proportions to determine if Cooper’s Hawks used valuable information on home range and habitat
the habitat types in their territories in proportion use of urban-breeding Cooper’s Hawks. Within
to their availability. We also recorded breeding suc- urban home ranges this species prefers areas that
cess of hawks in natural and urban areas. Home mimic natural settings. Management for this spe-
ranges did not differ between urban and natural cies in urban areas should emphasize providing
territories in the breeding season. In urban birds, this sort of habitat.
there was a trend of larger territories in the breed-
ing season compared to the non-breeding season. Key Words: Accipiter cooperii, adaptive kernel,
Cooper’s Hawks nesting in natural areas used breeding season, habitat use, home range, non-
coast live oak and riparian habitat more often breeding season, radiotelemetry, urban ecology.
H
abitat structure and resource availability hunting and foraging habitats (Boal and Mannan
are important factors that influence bird 1999), and these species can often be disturbed by
communities in both naturally occurring human activities near their nests (Fyfe and
and man-made environments. Predatory birds Olendorff 1976, Grier and Fyfe 1987, Richardson
may be especially sensitive to urbanization and Miller 1997). While food is perhaps the
because conversion of natural areas can reduce most important factor limiting raptor density
Chiang, S. N., P. H. Bloom, A. M. Bartuszevige, and S. E. Thomas. 2012. Home range and habitat use of Cooper’s Hawks in
urban and natural areas. Online (www.ucpress.edu/go/sab) in C. A. Lepczyk and P. S. Warren (editors). Urban bird ecology
and conservation. Studies in Avian Biology (no. 45), University of California Press, Berkeley, CA.
1
Lepczyk_5490022_online_CH08.indd 1 17/08/12 2:56 PM(Newton 1979, Pendleton et al. 1987), habitat and Craighead 1956, Murphy et al. 1988, Reynolds
alteration and/or destruction is recognized as the 1989) and southwestern portions of the species’
most important threat to accipiters (White 1974). range (Mannan and Boal 2000, Estes and Mannan
The conversion of native habitats to agriculture, 2003, Cartron et al. in press). However, no empiri-
industry, brush encroachment due to fire control cal studies of Cooper’s Hawk home ranges and
and grazing, wetland drainage, and urbanization habitat use in California exist. We are aware of
has been cited as causes of declines in raptor seven studies that investigated non-breeding sea-
numbers in the United States (Snyder and son ecology of this species such as home range
Snyder 1975). size (Craighead and Craighead 1956, Lake et al.
However, over the past decade, Cooper’s Hawk 2002), diet (Roth and Lima 2003, 2006), dispersal
(Accipiter cooperi) populations have increased and (Mannan et al. 2004), and wintering locality based
range expansions have been observed, especially on band recoveries (Henny 2004, Knutsen et al.
in the form of breeding birds colonizing urban 2004). The Lake et al. (2002) study is the most
and suburban areas (Curtis and Rosenfield 2006). similar to ours; they found that Cooper’s Hawks
Cooper’s Hawks have been reported to be toler- used forested habitats more often than expected
ant of some levels of human presence and habitat and used edges and open fields less than expected
alteration (Beebe 1974; Clark 1977; Rosenfield compared to availability. All of these studies have
et al. 1991, 1992) and have been observed nesting provided important data on home range, habitat
in urban environments (Beebe 1974, Stahlecker use, food habits, and predator–prey interactions
and Beach 1979, Murphy et al. 1988, Rosenfield of Cooper’s Hawks during the non-breeding sea-
et al. 1995, Sureda and Keane 1996, Kapler son and help to fill the data gap in the wintering
and Conrads 1997, Boal and Mannan 1998, ecology of this species.
DeCandido 2005). The ability of this species to We conducted a retrospective study of habi-
colonize certain urban environments suggests tat and space use by Cooper’s Hawks in Orange
that such information can be important for man- County, California, USA, using radiotelemetry.
agement, especially as urbanization continues One step in assessing the quality of an urban
(Boal and Mannan 1998). Furthermore, study- environment as habitat for a species is to compare
ing these birds in the urban environment, and that species’ breeding ecology and productivity
in particular studying reproductive success, is in urban versus natural areas (Gehlbach 1988,
important because it has been suggested that the Frimer 1989). Therefore, we also assessed repro-
urban environment can be an ecological trap for ductive success. The objectives of our study were
Cooper’s Hawks (Boal 1997). to determine home range and core area size of
Previous research on Cooper’s Hawks has adult male Cooper’s Hawks in areas with two lev-
focused on traditional and nontraditional breed- els of human disturbance (urban and natural) and
ing habitat. Traditional habitats consist of exten- to compare use of habitat types during the breed-
sive forests to small woodlots of deciduous, ing and non-breeding seasons. Based upon our
coniferous, and mixed-pine hardwoods (Meng objectives, we hypothesized that the following:
1951, Millsap 1981, Titus and Mosher 1981,
• Home range size and core areas of Cooper’s
Reynolds et al. 1982, Moore and Henny 1983,
Hawks in urban and natural areas will differ
Fischer 1986, Kennedy 1988, Wiggers and Kritz
in size. Specifically, we predicted that home
1991, Trexel et al. 1999, Curtis and Rosenfield
ranges and core area sizes will be smaller in
2006). In California, Cooper’s Hawks commonly
urban environments.
nest in oak woodlands dominated by coast live
oak (Quercus agrifolia) woodlands (Asay 1987). • Home range size and core areas of Cooper’s
Nontraditional breeding habitat consists of urban Hawks in urban and natural areas will differ
and suburban areas (Beebe 1974, Stahlecker and in the breeding and non-breeding season.
Beach 1979, Murphy et al. 1988, Rosenfield et al. Specifically, we predicted that home range
1995, Sureda and Keane 1996, Kapler and Conrads and core area will be larger in the breeding
1997, Boal and Mannan 1998, McConnell 2003, season compared to the non-breeding season.
Roth and Lima 2003, DeCandido 2005). • Habitat use by Cooper’s Hawks will be dis-
Spatial habitat requirements of Cooper’s tributed unequally across the entire home
Hawks have been studied in eastern (Craighead range. We predicted that in natural areas,
2 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 2 17/08/12 2:56 PMhawks will use oak woodland habitat in Elevation ranges from sea level to 1,710 m above
greater proportion than what is available mean sea level (County of Orange 2005).
in the home range and that urban hawks The county contains local and neighborhood
will use mature ornamental landscaping in parks, greenbelts, windrow-lined streets, and
greater proportion than what is available in channelized creeks interspersed throughout the
the home range. urban environment, which provides mature land-
• Reproductive success in urban- and natural- scaping conducive to some urban-adapted wild-
breeding Cooper’s Hawks will differ. We pre- life like Cooper’s Hawks. Although the majority
dicted that natural hawks will fledge more of ornamental trees are nonnative eucalyptus
young than urban hawks. (Eucalyptus spp.), some parks and greenbelts con-
tain fragmented remnants of natural vegetation
comprised of mature willows (Salix spp.), coast
METHODS live oaks, and western sycamore (Platanus race-
Study Area mosa) trees.
At the time of this study, we were aware of 74
The study area encompasses 648 km2 of urban Cooper’s Hawk territories in natural settings, 11
and natural areas in Orange County, California, along the urban–rural interface, and 40 in urban
USA (Fig. B.1). Orange County has an estimated areas, from which we selected four urban and
human population of 2.94 million residents and four natural based on accessibility. We considered
is located in Southern California along the Pacific territories as sampling units.
Ocean, south of Los Angeles. The county covers Principal land uses in urban territories
approximately 2,066 km2, which includes 65 km include residential, commercial, and local parks.
of coastline and extends inland approximately Permanent and intermittent water sources within
30 km. The climate is Mediterranean, with an urban territories include channelized water-
average annual rainfall of 36 cm, most of which ways, man-made water features such as pools
occurs in February. Average annual relative or fountains, artificial ponds, and a few natural
humidity is 56%, with an average temperature of drainages. Three of the four urban territories are
22°C. Topography includes rolling hills and other located in park-like settings comprised of mature
low-elevation areas that are primarily urbanized, ornamental trees associated with schools and uni-
and canyons constituting remnant natural areas. versity campuses. One of our urban territories is
located in a semi-fallow agricultural area next to a
small park.
San Bernardino Principal land uses in natural territories
Los Angeles include agriculture, cattle ranching, nurseries,
gravel mining, and open space. Perennial and
Riverside
intermittent water sources within natural ter-
ritories include natural streams, drainages (Bell
Ora nge
Canyon, Verdugo Canyon, and San Juan Creek),
and stock ponds. With the exception of dirt roads,
utility poles, and scattered buildings, vegetation
communities in the natural territories are rela-
tively intact; certain areas are more heavily grazed
than others, and therefore are more disturbed.
Pacific
Ocean However, in general, the natural territories repre-
San Diego sent a contiguous tract of open space.
25
km Telemetry
All hawks were captured using dho-gaza traps
Figure B.1. Southern California study area located in Orange
County. Urban territories were primarily located in the with a Great Horned Owl (Bubo virginianus) as
central portion of the county and natural territories were a lure (Bloom 1987, Bloom et al. 1992), or using
located in the southern portion of the county. bal-chatri traps baited with house mice (Mus
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 3
Lepczyk_5490022_online_CH08.indd 3 17/08/12 2:56 PMmusculus, Berger and Mueller 1959). Each hawk disturb hawks while radio-tracking. Two to four
was weighed, measured, and banded with a U.S. bearings were taken to determine triangulated
Fish and Wildlife Service aluminum band and locations, and most bearings were taken from a
a plastic color band (Haggie Engraving). Age distance of 100–150 m. However, hawks occupy-
and sex were determined by plumage and molt ing urban territories were considerably more tol-
characteristics, body size, mass, and presence or erant of human activity and often flew to perches
absence of a brood patch. We fitted male hawks located ⬍20 m from observers, which resulted in
with a 6-g backpack-mounted radio transmitter exact location points. Location points for natu-
(Model RI-2C, Holohil Systems, Ltd.; Dunston ral territories were mapped on U.S. Geological
1972), attached with a 4-mm-wide Teflon strap Survey (USGS) 7.5-minute topographic quadrangles,
harness. Backpacks weighed less than 3% of and locations for urban territories were mapped
the birds’ body weight and transmitters had a on Thomas Brothers Quad-page maps (Thomas
life expectancy of 12 months. We observed each Brothers Maps 2001 and 2008).
radio-tagged hawk immediately following trans- To determine error associated with location
mitter attachment and within 48 hours of release; estimates, we conducted error tests in natural
each appeared to exhibit normal behaviors. (n ⫽ 15 with two bearings) and urban locations
Cooper’s Hawks exhibit sexual dimorphism (n ⫽ 15 with two bearings and n ⫽ 15 with three
and may consequently hunt different areas and to four bearings). We had an independent party
take differently sized prey items. Male Cooper’s place a transmitter in habitat and topographic con-
Hawks are the primary food provider during ditions where Cooper’s Hawks would be found.
nest building, incubation, and brooding peri- The test transmitter locations were recorded
ods (Jones 1979); therefore, we used point loca- with a Global Positioning System (GPS) unit,
tions obtained from males to estimate territory and the triangulated locations in natural habi-
metrics. Consequently, our results are more tats were mapped on USGS topographic maps
applicable to adult male Cooper’s Hawks than to while the triangulated positions in urban habitats
Cooper’s Hawks in general. We used a hand-held were mapped on Thomas Brothers Quad-page
radio receiver with a three-element Yagi antenna maps. Triangulated positions were then digitized
(Communications Specialists, Inc.) to locate and converted to Universal Transverse Mercator
tagged hawks during 2001. A total of 1,685 hours (UTM) coordinates using ArcGIS software (ver.
were spent radio-tracking adult male Cooper’s 9.2, ESRI, Redlands, CA). Distances between
Hawks during the breeding season (March–July) test transmitters and triangulated locations were
and non-breeding season (July–November). In measured by comparing UTM coordinates. The
most cases, birds were tracked all day from morn- average distance between the actual and the
ing roost (1 hour before sunrise) to night roost triangulated locations was what we considered to
(1 hour after sunset) (Bloom 1989), with locations be the average error associated with triangulated
recorded at approximately half-hour intervals. locations and mapping (44.5 ⫾ 22.0 m in
In order to minimize dependency between suc- natural areas with two bearings, 43.7 ⫾ 26.3 m in
cessive locations, we removed all location points urban areas with two bearings, 28.4 ⫾ 16.6 m
within 30 minutes of each other; 30 minutes was in urban areas with three to four bearings).
easily longer than the amount of time required
for a Cooper’s Hawk to fly from one end of its Analysis
home range to the other (White and Garrott 1990,
Otis and White 1999). We developed an ArcView Home range estimates were calculated using
script to randomly filter 30-min locations from CALHOME (Kie et al. 1994) via the adaptive ker-
the data set equally throughout our survey period, nel (AK) method (Worton 1989), using the 95%
and night and morning roost locations from con- contour level and 50 m ⫻ 50 m grid size. Core
secutive observation days were removed. The total areas were calculated via the AK method with a
number of locations used to generate home range 50% contour level and 50 m ⫻ 50 m grid size.
estimates was 2,559 points. We determined the The estimated optimum bandwidth (least-squares
locations of radio-tagged hawks by direct obser- cross-validation score; Worton 1989) was used
vation accompanying radio locations (18.6%) as the smoothing parameter for all home range
and triangulation (81.4%). Care was taken not to estimates.
4 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 4 17/08/12 2:56 PMIn order to determine if enough location points (3) grassland, (4) riparian, (5) coast live oak,
were obtained to adequately describe home ranges, (6) aquatic, (7) agriculture, (8) developed, and
home range estimates were plotted against sample (9) ornamental landscaping. We categorized
sizes. Area-observation curves for the UCI territory urban habitat into one of ten types based on
(n ⫽ 206) showed that an adequate number of loca- Orange County Habitat Classification Maps:
tions was collected when approximately 95 points (1) urban, (2) rural residential, (3) commercial/
were obtained (Odum and Kuenzler 1955). However, industrial, (4) transportation, (5) parks/ornamen-
area-observation curves for the smallest sample size tal plantings, (6) cleared or graded areas, (7) natu-
revealed that an inadequate number of locations ral areas, (8) agriculture, (9) other developed, and
was collected (S. Preusker, n ⫽ 81). However, due to (10) other disturbed.
the small sample size of the study, this territory was We overlaid 50% AK and 95% AK home range
still included in the home range analysis. As such, estimates onto Orange County GIS vegetation
home range size for S. Preusker should be consid- data with a ground resolution of 1 m (County of
ered a minimum estimate. Consequently, combined Orange 1992) using ArcView and ArcGIS soft-
home range estimates for natural territories may ware (ESRI 1998, 2002). The resulting polygons
also be underestimated. were overlaid onto orthophotos to ground-truth
We determined if home range sizes differed vegetation data. A G-test of proportions (Sokal
between natural and urban birds in the breed- and Rohlf 1995) was used to test whether hawks
ing and non-breeding season by comparing used habitat within their territories in proportion
means and 99% confidence intervals (CI) of 95 to the available habitat.
AK and 50 AK home range sizes. Assessing dif-
ferences with confidence intervals is appropriate
RESULTS
in observational studies with low sample sizes
(Johnson 1999). We used 99% CI (instead of Nine male Cooper’s Hawks were fitted with radio
95% CI) as a correction for multiple compari- transmitters. However, one urban male did not
sons. If confidence intervals were overlapping, establish a territory, left the area within two weeks
we interpreted this as a lack of statistical differ- of transmitter attachment, and was excluded from
ence. However, if confidence intervals did not the study. Breeding-season home range esti-
overlap the mean, we interpreted this as support mates were subsequently determined for eight
for a trend toward statistical difference (Ramsey hawks. Non-breeding season home range esti-
and Schafer 2002). mates were determined for five hawks. Two males
(S. Preusker and Starr Mesa) vacated the area fol-
Reproductive Success lowing nest failure, while a third male (Verdugo
Canyon) fledged young but vacated the area fol-
In addition to radio-tracking, general nest obser- lowing post-fledging. Subsequent attempts to
vations were made throughout the breeding cycle, relocate hawks via hiking, driving, and aerial
including nestling development, timing of fledg- surveys via small fixed-wing plane were unsuc-
ing, and reproductive success. Reproductive suc- cessful; all three males left before enough
cess was determined by the number of young that non-breeding season points could be collected
successfully fledged the nest. and were excluded from non-breeding season
analysis. Approximately one-quarter of non-
Habitat Use breeding season location points for The Nature
Conservancy (TNC) male were obtained via direct
We used the Orange County Habitat Classification observation after we discovered that the antenna
System as the basis for our habitat classifications had been pulled out.
(County of Orange 1992). Descriptions of natural
plant communities follow the categories set forth
Home Range
by Holland (1986) and are described in detail in
Chiang (2004). We categorized natural habitat Breeding-season home ranges in natural
into one of nine communities based on domi- areas ranged between 378.0 ha and 1,080.0 ha
nant vegetation and physiognomic features of the (Table B.1). Breeding-season home ranges in
landscape: (1) coastal sage scrub, (2) chaparral, urban areas ranged between 344.0 ha and 630.6 ha
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 5
Lepczyk_5490022_online_CH08.indd 5 17/08/12 2:56 PMTABLE B.1
Seasonal core areas (50% AK) and home range (95% AK) estimates (ha) of adult male Cooper’s Hawks
in Orange County, March through November 2001.
Breeding Non-breeding
Territory n 50% AK 95% AK n 50% AK 95% AK
Natural
Amantes Campa 214 40.63 378.00 104 20.03 221.10
Verdugo Canyon b
277 62.65 1,080.00 — — —
Starr Mesab 92 62.98 557.00 — — —
S. Preuskerb 81 47.90 419.60 — — —
Urban
TNC 295 12.56 351.10 101 21.39 159.30
UCI 206 63.77 344.00 230 54.61 294.30
Saddleback 207 40.10 595.50 272 15.78 128.60
Venado 306 23.91 630.60 174 25.95 368.00
a
Data for the Amantes Camp non-breeding season were not included in any statistical analysis. The data are included here for
completeness.
b
Vacated territory before sufficient non-breeding season data was collected and was therefore excluded from non-breeding season
analysis.
(Table B.1). Only one home range was found further away from the nest. Mean distance of
for a non-breeding territory in a natural area roost sites during the latter portion of the breed-
(221.1 ha). Non-breeding home ranges in urban ing season through the non-breeding season was
areas ranged between 128.6 ha and 368.0 ha 608 ⫾ 361 m (mean ⫾ 95% CI). The other four
(Table B.1). Average home range size for males (Amantes Camp, Starr Mesa, S. Preusker,
Cooper’s Hawks in natural territories during Saddleback) used several different roosts through-
the breeding season was 609 ⫾ 416 ha (mean ⫾ out the breeding and non-breeding seasons.
99% CI), and average home range for urban
territories was 481 ⫾ 198 ha. Home ranges did Core Areas
not differ between urban or natural territories in
the breeding season. In urban birds, there was a On average, core areas represented 9.0 ⫾ 3.5%
trend (CI do not overlap the means) of larger ter- and 12.4 ⫾ 4.7% (mean ⫾ 95% CI) of the over-
ritories in the breeding season compared to the all breeding and non-breeding home ranges,
non-breeding season (Fig. B.2a). Comparisons respectively. Breeding-season core areas in natu-
between non-breeding birds in urban versus ral areas ranged between 40.6 ha and 63.0 ha.
natural habitats and non-breeding versus breed- Breeding-season core areas in urban areas ranged
ing in natural habitats could not be made due between 12.6 ha and 63.8 ha. Only one core area
to lack of sample size in non-breeding birds in was found for a non-breeding territory in a nat-
natural habitats. ural area (20.0 ha). Non-breeding core areas in
Mean distance of roost sites from the nest urban areas ranged between 15.8 ha and 54.6 ha.
during early and middle stages of the breeding In the breeding season, there was evidence that
season (incubation through pre-fledging) was core areas were larger for birds in natural areas
296 ⫾ 132 m (mean ⫾ 95% CI). As the breed- compared to urban areas (Fig. B.2b). In urban
ing season progressed and fledglings approached birds, there was no trend between breeding and
independence, half of the males (Verdugo Canyon, non-breeding birds. Comparisons between non-
TNC, UCI, Venado) used different roosts located breeding birds in urban versus natural habitats
6 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 6 17/08/12 2:56 PM1200
Uneven overlap of confidence intervals indicates
A)
a trend for higher reproductive success in urban-
Mean 95 AK home range size (ha)
1000 versus natural-breeding hawks.
800
Habitat Use
600 Percentages of habitat types, especially percent-
age of developed areas, varied considerably
400 between urban and natural territories. Developed
areas included shopping plazas, parking lots,
200
residential units, industrial buildings, schools,
and university campuses. Developed areas were
0
the most abundant habitat type in urban territo-
Breeding Non-breeding
ries, often accounting for more than 50% of avail-
Natural Urban
able habitat, whereas developed areas only rep-
resented at most 15% of available habitat within
natural territories. In contrast, coastal sage scrub
was the most abundant habitat type in natural ter-
80
B) ritories, often accounting for more than 20% of
70 available habitat.
Mean 50AK home range size (ha)
Habitat used by hawks differed significantly
60
from what was available within home ranges for
50 breeding birds in both urban (G ⫽ 22.9, df ⫽ 9,
P ⬍ 0.05) and natural (G ⫽ 17.1, df ⫽ 9, P ⬍ 0.05)
40
habitats. Urban breeding birds used parks/
30
ornamental plantings and commercial/industrial
areas more often than expected, and transportation
20 and natural areas less than expected (Fig. B.3).
However, confidence intervals are large and dem-
10
onstrate trends. Natural-breeding birds used coast
0 live oak and riparian areas more than expected
Breeding Non-breeding and chaparral, agriculture, and developed areas
Natural Urban
were used less than expected (Fig. B.4). Non-
breeding birds in urban habitat did not use
Figure B.2. Comparison of (a) 95% AK breeding and non- habitat within home ranges differently (G ⫽ 6.6,
breeding home ranges between natural and urban territories df ⫽ 7, P ⬎ 0.05). Non-breeding birds in natural
and (b) 50% AK breeding and non-breeding core areas habitats could not be tested because telemetry
between natural and urban territories. data was collected on only one bird.
All nests in natural territories were located in
and non-breeding versus breeding in natural hab- coast live oaks. Three of the four urban nests were
itats could not be made due to lack of sample size located in eucalyptus trees, and the fourth was in
in non-breeding birds in natural habitats. a Fremont’s cottonwood (Populus fremontii ssp.
fremontii). All urban nest groves contained tall,
Reproductive Success mature trees that were predominantly eucalyptus.
Nest height was measured during nestling
All four urban Cooper’s Hawks successfully banding or with a clinometer; nests averaged
fledged young (3.75 ⫾ 0.5; mean ⫾ 95% CI); 15.4 ⫾ 3.46 m (mean ⫾ 95% CI) above ground
however, only two natural Cooper’s Hawks suc- and were typically located in the upper one-third
cessfully fledged young (1.5 ⫾ 1.9). The other two of the nest tree. Average diameter at breast height
natural nests failed because of unknown causes. (DBH) for all nest trees was 254.0 ⫾ 92.16 cm
However, in both cases the eggs were scavenged. (mean ⫾ 95% CI).
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 7
Lepczyk_5490022_online_CH08.indd 7 17/08/12 2:56 PM80
70
60
50
Percent
40
30
20
10
0
re
n
n
s
er
al
al
d
d
a
rk
tio
l
e
ltu
re
tia
ci
th
ur
rb
Pa
rb
ta
er
a
O
u
at
en
U
tu
le
or
ric
m
N
id
C
is
sp
om
Ag
s
D
re
an
C
Tr
al
ur
R
Urban habitat type
Available Used
Figure B.3. Available versus used habitat for urban breeding birds. Urban-breeding birds used
parks/ornamental plantings and commercial/industrial areas more often than expected.
50
45
40
35
30
Percent
25
20
15
10
5
0
n
re
tic
s
er
l
ed
b
ak
d
rra
ria
rk
ru
tu
ua
th
an
Pa
op
O
a
ul
pa
sc
O
Aq
sl
ip
ric
el
e
ha
as
R
ge
liv
ev
Ag
gr
C
sa
D
st
al
oa
al
nu
C
st
An
oa
C
Natural habitat type
Available Used
Figure B.4. Available versus used habitat for natural breeding birds. Natural-breeding birds used
coast live oak and riparian habitat more often than expected.
Lepczyk_5490022_online_CH08.indd 8 17/08/12 2:56 PMDISCUSSION and our sample size is small. Further studies with
increased sample sizes are needed to understand
Home Range the relationship between urban and natural home
Average home range size for Cooper’s Hawks ranges of Cooper’s Hawks in Orange County.
in natural territories during the breeding season
was 609 ⫾ 416 ha and average home range for Core Areas
urban territories was 481 ⫾ 198 ha. Our find-
ings for home range size of Cooper’s Hawks It is not surprising that urban Cooper’s Hawks
during the breeding season in Orange County tended to have smaller core areas, because an
falls within the lower range of previous studies. urban hawk has a limited number of suitable
Previous home range estimates for breeding mature nest groves of adequate size compared to
Cooper’s Hawks range from 400 to 1,800 ha based natural settings that have essentially intact habi-
on nest density studies in natural areas without tat with a mosaic of woodlands and tree groves.
the benefit of telemetry (Craighead and Craighead Cooper’s Hawks in urban settings are limited by
1956, Reynolds 1989) and from an average of an inconsistent number and more random loca-
65.5 ha to 1,206 ha based on telemetry studies tion of landscaped trees that are tall enough and
in urban and natural areas (Murphy et al. 1988, provide adequate canopy cover. Smaller urban
Mannan and Boal 2000, Cartron et al. in press). core areas could also result in a higher abundance
The data from S. Preusker, which did not meet of prey within the immediate vicinity of the nest.
the minimum required locations, likely lowered Urban Cooper’s Hawks were often seen hunting
our overall mean for home range size due to its at backyard bird feeders and bird baths immedi-
more conservative estimate. However, the home ately surrounding the nest grove throughout the
range estimate for this individual was neither the breeding and non-breeding seasons.
smallest nor the largest estimate. Therefore, we
believe that the average home range calculated Reproductive Success
is an accurate estimate. Furthermore, the home
ranges we calculated fit within the known range Although based on a small sample size, we believe
of areas for this species; therefore, we believe our that the high reproductive success rate of urban
data are reflective of the home range for this Cooper’s Hawks may be attributed, in part, to the
species in this area. fact that there are few, if any natural nest preda-
The average home range (481 ⫾ 198 ha) for tors such as gray fox (Urocyon cinereoargenteus)
urban Cooper’s Hawks during the breeding sea- or bobcat (Lynx rufus) in the urban home ranges
son in Southern California falls within the middle in our study area (P. H. Bloom, unpubl. data).
range of other urban telemetry studies. Average Similar findings have been observed in Eastern
home range was smaller than the 784-ha average Screech-Owls (Megascops asio) in Texas (Gehlbach
in Wisconsin (Murphy et al. 1988) and consider- 1994) and urban Cooper’s Hawks in Pennsylvania
ably larger than the 65.5-ha average in Tucson, (McConnell 2003), where these species appar-
Arizona (Mannan and Boal 2000). ently benefited from decreased nest predation in
A variety of factors influence space use of rap- the urban setting. Raccoons (Procyon lotor) occa-
tors, including prey abundance, habitat availabil- sionally occur in the urban home ranges of our
ity, foraging behavior, and territoriality (Newton study area, but their numbers were believed to be
1979, Bloom et al. 1993). Beissinger and Osborne low and occurrences localized compared to natu-
(1982) suggested that urban areas support a ral areas. Therefore, we assume they do not pose
higher total density of birds than non-urban a substantial threat to nestling Cooper’s Hawks.
areas. Based on such evidence, urban Cooper’s Furthermore, the presence of domestic dogs
Hawks would be expected to have smaller home within the immediate vicinity of urban Cooper’s
ranges due to a higher biomass of birds within Hawk nests probably contributes significantly to
the area, as was the case in Tuscon (Boal 1997, reduced predation risk by mammals. Nest preda-
Estes and Mannan 2003). Home ranges did not tion by Great Horned Owls is a major cause of
differ between urban and natural territories in nestling mortality (Rosenfield 1988). Despite the
this study; however, confidence intervals are large fact that three of the four urban Cooper’s Hawk
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 9
Lepczyk_5490022_online_CH08.indd 9 17/08/12 2:56 PMterritories were located in the vicinity of Great in part, to sedentary behavior exhibited by male
Horned Owl nests (Bennett 1999, P. H. Bloom, Cooper’s Hawks following nestling independ-
unpubl. data), all of these territories successfully ence. This sedentary behavior was also observed
fledged young. We acknowledge that many urban during fledgling dispersal of urban Cooper’s
Cooper’s Hawks in other portions of the species’ Hawks in Arizona (Mannan et al. 2004). Whereas
range must contend with the previously men- Cooper’s Hawks during the breeding season
tioned nest predators; however, Cooper’s Hawks were constantly moving from perch to perch
in our urban study area may have benefited from actively foraging and defending the territory
low numbers and localized occurrences. (Fischer 1986, Kennedy 1991), it was common
for a Cooper’s Hawk during the non-breeding
Winter Residency and Non-breeding season to remain perched in the same location
Season Ecology for several hours at a time (up to 8 hours; Chiang
2004). The change in daily activity pattern is a
Relatively little data exist on winter residency function of parental responsibility. During the
among accipiters, and on Cooper’s Hawks in par- breeding season, adult male Cooper’s Hawks
ticular, during the non-breeding season. Banding are active because they must constantly hunt to
data in Wisconsin based on winter recaptures feed the female during incubation and brooding,
of marked birds indicate that some of that state’s feed the young, and defend the territory. During
Cooper’s Hawks may overwinter within 1 to 2 km the non-breeding season, adult male Cooper’s
of their previous nest sites (Bielefeldt et al. 1998). Hawks need only hunt for themselves. Activity
Band recoveries in Michigan also indicate winter beyond what is necessary for survival increases
site fidelity (Knutsen et al. 2004). Data on winter the risk of mortality.
home range size of unmarked Cooper’s Hawks
range from 2.4 to 3.2 km in diameter (Craighead Habitat Use
and Craighead 1956) to an average of 771 ha for
marked fledglings (Mannan et al. 2004) and 331 Habitat used by hawks differed significantly
to 836 ha for marked juveniles and adults (Lake from what was available within home ranges in
et al. 2002). Our findings follow winter residency both natural and urban environments. Cooper’s
patterns of Cooper’s Hawks in Wisconsin (Bielefeldt Hawks in natural areas of our study area used
et al. 1998), Michigan (Knutsen et al. 2004), and coast live oak and riparian areas more than
Arizona (Mannan et al. 2004), and suggest that expected. Specifically, the coast live oak habitat
Cooper’s Hawks in Southern California appear to be often occurred in association with riparian areas,
year-round residents and remain close to their nest suggesting this species’ strong association to
stands during winter (Chiang 2004). Average home riparian woodland vegetation. Other studies have
range size of Cooper’s Hawks in Orange County documented Cooper’s Hawks in undeveloped,
during the non-breeding season was 237 ha (urban) extensive forests to small woodlots of decidu-
and 221 ha (natural), which is much smaller than ous, coniferous, and mixed-pine hardwoods, and
the average of 771 ha for fledgling Cooper’s Hawks coast live oak woodlands (Meng 1951, Asay 1980,
in Tucson, Arizona (Mannan et al. 2004), and mod- Millsap 1981, Titus and Mosher 1981, Reynolds
erately smaller than the range of 331 to 836 ha for et al. 1982, Moore and Henny 1983, Fischer 1986,
juvenile and adult Cooper’s Hawks in southwestern Kennedy 1988, Wiggers and Kritz 1991, Curtis
Tennessee (Lake et al. 2002). and Rosenfield 2006). Breeding Cooper’s Hawks
Cooper’s Hawks feed primarily on birds dur- in urban sites within our study area used parks/
ing winter (Craighead and Craighead 1956), ornamental plantings and commercial/industrial
especially medium–large birds ⬎70 g in urban areas within their home ranges more often than
areas (Roth and Lima 2003) and small birds such expected. It is likely that parks/ornamental plant-
as sparrows in rural areas (Roth and Lima 2006). ings and commercial/industrial areas within
Southern California has an abundant wintering the urban home ranges adequately mimicked
bird population on which Cooper’s Hawks may natural woodlands in terms of habitat structure.
be able to subsist in smaller home ranges. The Studies of non-traditional breeding habitat have
trend of smaller non-breeding season home shown Cooper’s Hawks to be successful breed-
ranges in urban territories can also be attributed, ers in a variety of urban settings with different
10 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 10 17/08/12 2:56 PMlevels of human disturbance (Stahlecker and that hunt exclusively from perches (Bloom et al.
Beach 1979, Murphy et al. 1988, Rosenfield et al. 1993), Cooper’s Hawks employ a variety of hunt-
1995, Sureda and Keane 1996, Boal 1997, Boal ing techniques and therefore are not limited by
and Mannan 1998, DeCandido 2005). However, perch availability.
habitat data were evaluated for a relatively small Previous studies of urban-nesting raptors in
number of birds (n ⫽ 4 for natural hawks during Southern California include Red-shouldered
the breeding season and n ⫽ 4 for urban hawks Hawks (Bloom and McCrary 1996) and Great
during each season, breeding and non-breeding). Horned Owls (Bennett and Bloom 2005).
Therefore, it is important that more studies of Additional raptor species that have been thor-
habitat use by Cooper’s Hawks be conducted, par- oughly monitored in Southern California include
ticularly in urban areas where habitat use is not as Red-tailed Hawk (Buteo jamaicensis), Northern
well documented. Regardless, our results provide Harrier (Circus cyaneus), and White-tailed Kite
valuable information about the types of habitat in (Elanus leucurus; P. H. Bloom, unpubl. data, Niemela
which Cooper’s Hawks may be found. 2007). Of these species, Cooper’s Hawks and Red-
shouldered Hawks have been successful in the
Urban Ecology of Cooper’s Hawks urban environment in similar ways. Behaviorally,
both urban Cooper’s Hawks and Red-shouldered
Habitat use by raptors is greatly influenced by Hawks seemed undisturbed by human presence.
prey abundance, habitat structure, and perch High levels of human activity directly beneath
availability in relation to foraging technique Red-shouldered Hawk nest trees within the same
(Craighead and Craighead 1956, Newton 1979, study area did not result in nest abandonment
Newton et al. 1979, Janes 1985). Cooper’s Hawks (Bloom and McCrary 1996); however, some indi-
use a combination of prey-capture methods that viduals were aggressive toward people. In our
include brief perch-and-scan episodes to locate study, nest groves of all urban hawks were located
prey, followed by a sudden burst of speed in addi- in densely populated areas. Specifically, the UCI,
tion to hunting from higher flight (Meng 1951, Saddleback, and Venado nest groves were located
Mead 1963, Beebe 1974, Clark 1977, Fischer on university/school campuses where hundreds
1986). Kennedy (1991) described this hunting of college students and elementary school chil-
technique as saltatory foraging, which is charac- dren regularly walked and played directly below
terized by a stop-and-go pattern, where the ani- nest trees on a daily basis, often ⬍15 m from
mal repositions itself frequently to scan from a perched adults. Aggressive behavior (swoop-
new location (Evans and O’Brien 1988). Other ing flights and occasional strikes) in response to
hunting techniques employed by Cooper’s Hawks human presence was only observed from one pair,
in urban areas include the use of visual obstruc- but occurs regularly at other urban territories in
tions such as buildings, fences, and hedgerows Orange County. In comparison, Cooper’s Hawks
for surprise-ambush attacks on prey (Roth and in natural settings were skittish and extremely
Lima 2003). All of the aforementioned foraging sensitive to human presence. Similar to our find-
techniques were observed during radio-tracking. ings, Bloom and McCrary (1996) also observed
Due to the fact that Cooper’s Hawks typically rely smaller home ranges and higher reproductive
on concealment and take prey from the ground, success with urban Red-shouldered Hawks than
in flight, or from perches, it is not surprising that those in natural areas.
Cooper’s Hawks used woodland habitats more Factors that contribute to the success of urban
than non-woodland habitats. Woodland habitats Cooper’s Hawks include their foraging technique,
provide numerous perch sites and cover necessary characterized by maneuverability in structur-
for successful hunting by a predator that relies on ally complex habitats, in addition to the fact that
concealment. Cooper’s Hawks in the study area their prey base consists primarily of small to
were seen hunting and feeding on avian prey medium-sized birds that are abundant in urban
more often than mammalian or reptilian spe- areas. Therefore, their surprise-ambush forag-
cies, and urban Cooper’s Hawks were regularly ing technique (Roth and Lima 2003) is successful
seen hunting within hedgerows and from fences in the urban setting. Likewise, the perch-and-
above hedgerows. Unlike other raptor species wait hunting style of Red-shouldered Hawks
such as Red-shouldered Hawks (Buteo lineatus) is facilitated in the urban landscape through
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 11
Lepczyk_5490022_online_CH08.indd 11 17/08/12 2:56 PMabundant lampposts, fence lines, and utility poles. years ago, the landscaped vegetation in our urban
Additionally, their prey base consists of small ver- study area was not mature enough to provide the
tebrate and invertebrate species that are abundant height and canopy cover that could mimic natural
in urban areas (Bloom et al. 1993). Although prey woodlands and groves. Therefore, until that time
species composition differs between urban and the urban landscape was not suitable for urban
natural Cooper’s Hawks (Estes and Mannan 2003, Cooper’s Hawks. Even now, after 50 to 70 years of
Roth and Lima 2006), the urban hawks forage on urban forest growth and development, there are
substitute species that still fit within the param- many square kilometers of Orange County that
eters of their typical natural prey base. Urban do not support nesting Cooper’s Hawks because
Cooper’s Hawks were often seen hunting at back- of the short structure of certain tree species that
yard bird feeders and bird baths throughout the were planted.
breeding and non-breeding seasons. Despite the fact that oak woodlands are
After considering the raptor species that are covered in the Central Coastal Subregion Natural
present and absent from the urban environment Communities Conservation Plan, a regional
in Southern California, we believe that diet plan designed to protect habitat and aid in the
and hunting style are two ecological traits that recovery of the federally listed Coastal California
significantly contribute to success in human- Gnatcatcher (Polioptila californica californica;
altered landscapes. Cooper’s Hawks and Red- County of Orange 1996), a substantial portion of
shouldered Hawks have been able to successfully the remaining oak woodlands and surrounding
adapt to the urban environment in our study habitat in our natural study area are slated for
area because they employ hunting styles that are development over the next 20 years. Although
facilitated by features in the urban setting, in the urban Cooper’s Hawk population in Southern
addition to the fact that they are not limited by California suggests this species’ flexibility in an
prey availability. urban setting, urbanization in other portions of
the species’ range has been detrimental to both
urban- and natural-nesting birds (Bosakowski
MANAGEMENT IMPLICATIONS
et al. 1993, Boal 1997). For instance, despite the
A study of Northern Goshawk home ranges within higher fledging success of urban birds, which
timber management areas placed an empha- suggests that urban areas may produce more
sis on home range management rather than young, two adult urban Cooper’s Hawks died as
just nest site protection (Hargis et al. 1994). We a result of car collisions after radio-tracking had
fully agree and believe that home range manage- ended. Roth et al. (2005) cite human-induced
ment, especially within urban areas, will become mortality factors, including collisions with
increasingly important for species conservation windows or automobiles (Keran 1981, Klem
as development continues. Increasing popula- 1990, Klem et al. 2004), electrocution (Lehman
tion demands have led to rapid urbanization in 2001), natural predation by owls and other raptors
Southern California, resulting in considerable (Klem et al. 1985, George 1989, Roth et al. 2005),
native habitat loss. Estimates of regional coastal disease (Ward and Kennedy 1996, Boal et al.
sage scrub habitat loss range from 66% to 90% 1998), and to a lesser degree, gunshot and poison
(County of Orange 1996). Oak woodlands are also (Boal 1997). A more detailed demographic study
becoming increasingly rare in Orange County. including reproductive success and juvenile and
Significant conversion of agricultural land to adult survivorship in urban and natural areas
the current urban landscape in Orange County would provide a more robust analysis of whether
began in the 1940s (County of Orange 2005). It the urban setting in Southern California is an
was not until 1998 that P. H. Bloom (unpubl. ecological trap.
data) noted the first successful nesting attempt Trend analysis from the North American
of Cooper’s Hawks in the urban setting of his Breeding Bird Survey (BBS) for 1980 to 2007
neighborhood. While some older neighborhoods indicates a survey-wide increase in Cooper’s
frequently contained Cooper’s Hawk nesting Hawk populations of 4.6% per year, with a 5.9%
territories, vast areas of urban Orange and Los increase per year in the United States and a 5.7%
Angeles Counties do not contain nesting Cooper’s decrease per year in Canada (Sauer et al. 2008).
Hawks. We contend that until approximately ten Most of the increase has occurred in northern and
12 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 12 17/08/12 2:56 PMeastern portions of the survey area, while declin- Berger, D. D., and H. C. Mueller. 1959. The bal-chatri
ing populations have been observed in western trap for the birds of prey. Bird Banding 30:18–26.
portions of the survey area, including Canada and Bielefeldt, J., R. N. Rosenfield, W. E. Stout, and
most of California. Specifically within California S. M. Vos. 1998. The Cooper’s Hawk in Wisconsin:
and California foothills, trend analyses indicate a review of its breeding biology and status. Passenger
Pigeon 60:111–121.
a 5.2% and 7.1% decrease, respectively, per year
Bloom, P. H. 1987. Capturing and handling raptors.
for the same time period. Despite the decreasing
Pp. 99–123 in B. A. Pendleton, B. A. Millsap, K. W.
population trend in California, Cooper’s Hawks
Cline, and D. A. Bird (editors), Raptor management
have recently been downgraded from a California techniques manual. Science Technical Series No. 10.
Species of Special Concern to a Watch List National Wildlife Federation, Washington, DC.
Species. Therefore, effective conservation plan- Bloom, P. H. 1989. Red-shouldered Hawk home range
ning and management in California should be and habitat use in southern California. M.S. thesis,
actively pursued in light of decreased regulatory California State University, Long Beach, CA.
oversight and continued habitat loss. Bloom, P. H., J. L. Henckel, E. H. Henckel, J. K.
Schumtz, B. Woodbridge, J. R. Bryan, R. L. Anderson,
ACKNOWLEDGMENTS P. J. Detrich, T. L. Maechtle, J. O. McKinley, M. D.
McCrary, K. Titus, and P. F. Schempf. 1992. The
We would like to thank C. Tischer, L. Allen, C.
dho-gaza with Great Horned Owl lure: an analysis
deBeauvoir, S. deBeauvoir, S. Sheakely, A. Pettis, J.
of its effectiveness in capturing raptors. Journal of
Walcek, S. Stoffel, and S. Stewart for their countless
Raptor Research 26:167–178.
hours of radio-tracking; L. Backus, Z. Henderson,
Bloom, P. H., and M. D. McCrary. 1996. The urban
and J. Hall for their GIS expertise; and S. Porter of
buteo: Red-shouldered Hawks in southern Califor-
Communications Specialists, Inc., who donated much
nia. Pp. 31–39 in D. M. Bird, D. E. Varland, and
of the telemetry equipment. Partial funding for this
J. J. Negro (editors), Raptors in human landscapes:
study was provided by Sea and Sage Audubon Society
adaptation to built and cultivated environments.
and The Wildlife Society, Western Section. We thank
Academic Press, San Diego, CA.
Rancho Mission Viejo, Caspers Wilderness Park, Starr
Bloom, P. H., M. D. McCrary, and M. J. Gibson. 1993.
Ranch Audubon Sanctuary, and The Nature Conserv-
Red-shouldered Hawk home-range and habitat use
ancy for access to their land. Lastly, we thank J. Manning
in southern California. Journal of Wildlife Manage-
and the reviewers for comments that greatly improved
ment 57:258–265.
the manuscript.
Boal, C. W. 1997. An urban environment as an ecolo-
gical trap for Cooper’s Hawks. Ph.D. dissertation,
LITERATURE CITED
University of Arizona, Tucson, AZ.
Asay, C. E. 1980. Habitat, biology, and productivity Boal, C. W., and R. W. Mannan. 1998. Nest-site selec-
of Cooper’s Hawks nesting in the oak woodlands tion by Cooper’s Hawks in an urban environment.
of California. M.S. thesis, University of California, Journal of Wildlife Management 62:864–871.
Davis, CA. Boal, C. W., and R. W. Mannan. 1999. Comparative
Asay, C. E. 1987. Habitat and productivity of Cooper’s breeding ecology of Cooper’s Hawks in urban and
Hawks nesting in California. California Depart- exurban areas of southeastern Arizona. Journal of
ment of Fish and Game 73:80–87. Wildlife Management 63:77–84.
Beebe, F. L. 1974. Field studies of the falconiformes of Boal C. W., R. W. Mannan, and K. Stormy Hudelson.
British Columbia: vultures, hawks, falcons, eagles. 1998. Trichomoniasis in Cooper’s Hawks from
British College Proceedings Museum Occasional Arizona. Journal of Wildlife Diseases 34:590–593.
Paper No. 17. Victoria, BC, Canada. Bosakowski, T., R. Speiser, D. G. Smith, and L. J.
Beissinger, S. R., and D. R. Osborne. 1982. Effects of Niles. 1993. Loss of Cooper’s Hawk nesting habitat
urbanization on avian community organization. to suburban development: inadequate protection
Condor 84:75–83. for a state-endangered species. Journal of Raptor
Bennett, J. R. 1999. Home range and habitat use by Research 27:26–30.
Great Horned Owls in southern California. M.S. Cartron, J. L., P. L. Kennedy, P. Yaksich, and S. H.
thesis, California State University, Long Beach, CA. Stoleson. In press. Cooper’s Hawk (Accipiter coope-
Bennett, J. R., and P. H. Bloom. 2005. Home range rii). In J. L. Cartron (editor), Raptors of New Mexico.
and habitat use by Great Horned Owls (Bubo vir- University of New Mexico Press, Albuquerque, NM.
ginianus) in southern California. Journal of Raptor Chiang, S. N. 2004. Home range and habitat use of
Research 39:119–126. Cooper’s Hawks in urban and natural areas of
HOME RANGE AND HABITAT USE OF COOPER’S HAWKS 13
Lepczyk_5490022_online_CH08.indd 13 17/08/12 2:56 PMsouthern California. M.S. thesis, California State George, J. R. 1989. Bald Eagle kills Sharp-shinned
University, Fullerton, CA. Hawk. Journal of Raptor Research 23:55–56.
Clark, R. J. 1977. Cooper’s Hawk hunting in the city. Grier, J. W., and R. W. Fyfe. 1987. Preventing research
Auk 94:142–143. and management disturbance. Pp. 173–182 in
County of Orange. 1992. Habitat classification system B. A. Pendleton, B. A. Millsap, K. W. Cline, and
natural resources Geographic Information System D. A. Bird (editors), Raptor management tech-
(GIS) project. Planning and Development Services niques manual. Science Technical Series No. 10.
Department, Santa Ana, CA. National Wildlife Federation, Washington, DC.
County of Orange. 1996. Central and coastal sub- Hargis, C. D., C. McCarthy, and R. D. Perloff. 1994.
region natural community conservation plan/habitat Home ranges and habitats of Northern Goshawks in
conservation plan. R. J. Meade Consulting, Inc. eastern California. Studies in Avian Biology 16:66–74.
La Jolla, CA. Henny, C. J. 2004. Wintering localities of Cooper’s
County of Orange. 2005. County of Orange general Hawks nesting in northeastern Oregon. Journal of
plan. Resources and Development Management Field Ornithology 61:104–107.
Department, Santa Ana, CA. Holland, R. F. 1986. Preliminary descriptions of the
Craighead, J. J., and F. C. Craighead. 1956. Hawks, terrestrial natural communities of California. Un-
owls, and wildlife. Stackpole Company and Wildlife published report available from California Depart-
Management Institute, New York. ment of Fish and Game.
Curtis, O. E., and R. N. Rosenfield. 2006. Cooper’s Janes, S. W. 1985. Habitat selection in raptorial birds.
Hawk (Accipiter cooperii). No. 75 in A. Poole (editor), Pp. 159–188 in M. Cody (editor), Habitat selection
The birds of North America. Cornell Laboratory of in birds. Academic Press, New York, NY.
Ornithology, Ithaca, NY. Johnson, D. H. 1999. The insignificance of statistical
DeCandido, R. 2005. First nesting of Cooper’s Hawks significance testing. Journal of Wildlife Manage-
(Accipiter cooperii) in New York City since 1955. ment 63:763–772.
Journal of Raptor Research 39:109. Jones, S. 1979. Habitat management series for unique
Dunston, T. C. 1972. Radio-tagging Falconiform and or endangered species. Report 17: The Accipiters.
Strigiform birds. Raptor Research 6:93–102. Technical Note No. 335. U.S. Department of Inte-
Estes, W. A., and R. W. Mannan. 2003. Feeding beha- rior, Bureau of Land Management.
vior of Cooper’s Hawks at urban and rural nests in Kapler, J. E., and D. J. Conrads. 1997. Notes on an
southeastern Arizona. Condor 105:107–116. urban nesting Cooper’s Hawk in Dubuque, Iowa.
Evans, B. I., and W. J. O’Brien. 1988. A re-analysis Iowa Bird Life 67:73–77.
of the search cycle of a planktivorous salmonid. Kennedy, P. L. 1988. Habitat characteristics of
Canadian Journal of Fisheries and Aquatic Sciences Cooper’s Hawks and Northern Goshawks nesting
45:187–192. in New Mexico. Pp. 218–227 in R. Glinski, B. G.
Fischer, D. L. 1986. Daily activity patterns and habi- Pendleton, M. B. Moss, B. A. Millsap, and S. W.
tat use of coexisting accipiter hawks in Utah. Ph.D. Hoffman (editors), Proceedings from the southwe-
dissertation, Brigham Young University, Provo, UT. stern raptor management symposium and work-
Frimer, O. 1989. Breeding performance in a Danish sub- shop. National Wildlife Federation Science Techni-
urban population of sparrowhawks, Accipiter nisus. cal Series No. 11. Washington, DC.
Dansk Ornitologisk Forenings Tidsskrift 83:151–156. Kennedy, P. L. 1991. Reproductive strategies of
Fyfe, R. W., and R. R. Olendorff. 1976. Minimizing the Northern Goshawks and Cooper’s Hawks in
dangers of nesting studies to raptors and other sen- north-central New Mexico. Ph.D. dissertation, Utah
sitive species. Canadian Wildlife Service Occasional State University, Logan, UT.
Paper No. 23. Ottawa, ON, Canada. Keran, D. 1981. The incidence of man-caused and
Gehlbach, F. R. 1988. Population and environmen- natural mortalities to raptors. Journal of Raptor
tal features that promote adaptation to urban Research 15:108–112.
ecosystems: the case of Eastern Screech-Owls Kie, J. G., J. A. Baldwin, and C. J. Evans. 1994.
(Otus asio) in Texas. Pp. 1809–1813 in H. Ouellet CALHOME: home range analysis program elec-
(editor), Proceedings of the 19th International Orni- tronic user’s manual. U.S. Forest Service, Pacific
thological Congress, Vol. 2. University of Ottawa Southwest Research Station, Albany, CA.
Press, Ottawa, ON, Canada. Klem, D., Jr. 1990. Collisions between birds and
Gehlbach, F. R. 1994. The Eastern Screech-Owl: life windows: mortality and prevention. Journal of Field
history, ecology, and behavior in suburbia and the Ornithology 61:120–128
countryside. Texas A&M University Press, College Klem, D., Jr., B. S. Hillegass, and D. A. Peters. 1985.
Station, TX. Raptors killing raptors. Wilson Bulletin 97:230–231.
14 STUDIES IN AVIAN BIOLOGY NO. 45 Lepczyk and Warren
Lepczyk_5490022_online_CH08.indd 14 17/08/12 2:56 PMYou can also read
