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Urban, suburban and rural Red-tailed Hawk nesting habitat and populations in southeast Wisconsin

  • Independent Research - Wildlife Biologist

Abstract and Figures

Nesting Red-tailed Hawks (Buteo jamaicensis) are becoming increasingly common in urban environments. We described Red-tailed Hawk nesting habitat and reproductive success and compared urban, suburban, and rural nesting locations in southeast Wisconsin. Nest sites were classified as urban, suburban or rural if ≥70%, 30-70%, or ≤30% of the area (706.9 ha, 1.5-km radius) around nests was used for industrial or residential purposes, respectively. Mean success and productivity of breeding Red-tailed Hawks in the metropolitan Milwaukee area from 1989-94 (N = 426) was 81.9% (range = 75.3-92.7%) and 1.43 young/breeding pair (range = 1.13-1.91), respectively. Brood size averaged 1.75 young/successful nest (range = 1.61-2.06). Productivity was variable and was significantly higher in 1994 than each of the preceding yr (P < 0.001). Based on internest distances, the density of the Red-tailed Hawk nesting population for rural locations was greater than in suburban areas and lowest in urban locations. The amount of natural microhabitat cover around nests (19.6 ha, 0.25-km radius) did not differ for urban, suburban, or rural nest sites (P = 0.967) indicating that cover was an important component of the nesting habitat of Red-tailed Hawks. Natural cover comprised about 16% of the landscape area of urban sites and 40% of this area was wooded with the remaining 60% consisting of herbaceous cover. Urban planning should consider the amount of natural cover to allow Red-tailed Hawks and other wildlife to coexist with humans in an urban environment.
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j Raptor Res. 32(3):221-228
¸ 1998 The Raptor Research Foundation, Inc.
W2364 Heather Street, Oconomowoc, 14/1 53066 U.S.A.
University of Wisconsin-Stevens Point, Stevens Point, 14/1 54481 U.S.A.
Rt. i Box 158A, Drummond, WI 54832 U.S.A.
ABSTR•CT.--Nesting Red-tailed Hawks (Buteo jamaicensis) are becoming increasingly common in urban
environments. We described Red-tailed Hawk nesting habitat and reproductive success and compared
urban, suburban, and rural nesting locations in southeast Wisconsin. Nest sites were classified as urban,
suburban or rural if ->70%, 30-70%, or <30% of the area (706.9 ha, 1.5-km radius) around nests was
used for industrial or residential purposes, respectively. Mean success and productivity of breeding Red-
tailed Hawks in the metropolitan Milwaukee area from 1989-94 (N = 426) was 81.9% (range = 75.3-
92.7%) and 1.43 young/breeding pair (range = 1.13-1.91), respectively. Brood size averaged 1.75
young/successful nest (range = 1.61-2.06). Productivity was variable and was significantly higher in
1994 than each of the preceding yr (P < 0.001). Based on internest distances, the density of the Red-
tailed Hawk nesting population for rural locations was greater than in suburban areas and lowest in
urban locations. The amount of natural microhabitat cover around nests (19.6 ha, 0.25-km radius) did
not differ for urban, suburban, or rural nest sites (P = 0.967) indicating that cover was an important
component of the nesting habitat of Red-tailed Hawks. Natural cover comprised about 16% of the
landscape area of urban sites and 40% of this area was wooded with the remaining 60% consisting of
herbaceous cover. Urban planning should consider the amount of natural cover to allow Red-tailed
Hawks and other wildlife to coexist with humans in an urban environment.
K•Y Worn)s: Red-tailed Hawk; Buteo jamaicensis; urban; suburban; rural; nesting habitat;, nesting density.
Habitat de anidaci6n urbano, suburbant y rural de Buteo jamaicensis en el sureste de Wisconsin
RESUMEN.--La anidacitn en •treas de Buteo jamaicensis es cada vez mas cornfin en ambientes urbanos.
Describimos el habitat de anidacitn de Buteo jamaicensis y su 6xito reproductivo y comparamos las
localidades urbanas, suburbanas y rurales de anidacitn en el sureste de Wisconsin. Los sitits de los
nidos fueron clasificados como urbanos, rurales y suburbanos si >70%, -<30%, y 30-70% del •rea (706.9
ha, 1.5 km de radio) alrededor del nido eran utilizadas para proptsitos industrial o residencial (desar-
rollo) respectivamenmte. La media del 6xito en la productividad de los nidos ocupados por Buteoja-
maicensis en el •rea metropolitana de Milwakee entre 1989-94 (N = 426) fue de 81.9% (rango = 75.3-
92.7%) y 1.43 juveniles/nido ocupado (rango = 1.13-1.91). Tamafio de la nidada promedit de 1.75
juveniles/nido exitoso (rango = 1.61-2.06). La productividad fue variable y significativamente mas alta
en 1994 queen cada uno de los afits precedentes (p < 0.0001). Con base en la distancia entre nidos
se observo que la densidad de la poblacitn reproductiva de las localidades rurales, fue mayor queen
las •reas suburbanas y fue menor en •reas urbanas. La cantidad de cobertura de microhabitat natural
alrededor de los nidos (19.6 ha, 0.25 km de radio) no fue diferente entre Its sitits de los nidos urbanos,
suburbanos y rurales (P = 0.967) lo cual indica que la cobertura es un componente importante del
habitat de anidacitn de Buteo jamaicensis. La cobertura natural incluyo el 16% del microhabitat de los
sitits urbanos, 40% de esta •rea eran bosques y el 60% restante eran cobertura de pastizales. La pla-
neacitn urbana debe considerar la cantidad de cobertura natural re•luerida para que Buteo jamaicensis
y la vida silvestre puedan coexistir con Its humanos en un ambiente urbano.
[Traduccitn de Ctsar M•rquez]
222 STOUT ET AL. VOL. 32, NO. 3
Red-tailed Hawks (Buteo jamaicensis) nest in ur-
ban environments, yet no comprehensive studies
have been published on their urban nesting habi-
tat. Two reports in Michigan document the suc-
cessful nesting of red-tails in urban settings (Val-
entine 1978, Hull 1980), and urban nesting also
has been reported in Puerto Rico (Santana et al.
1986) and New York (Minor et al. 1993).
Three studies of rural Red-tailed Hawk popula-
tions have previously been conducted in Wisconsin
(Orians and Kuhlman 1956, Gates 1972, Petersen
1979). Howell et al. (1978) correlated nesting hab-
itat structure and productivity at rural nest sites in
Ohio and found that highly productive sites had
more than twice as much fallow land, less than half
as much cropland, and less than half the number
of woodlots than did sites with low productivity.
Other studies of red-tails conducted in rural areas
throughout North America have described other
aspects of red-tail ecology (e.g., Wiley 1975, Fitch
and Bare 1978, Adamcik et al. 1979).
Our objectives were to describe Red-tailed Hawk
nesting habitat and reproductive success, and to
compare urban, suburban, and rural nesting loca-
tions in southeast Wisconsin. We determined rela-
tive nesting population densities for all three lo-
cations based on internest distances and identified
important physical components of the nesting hab-
Our study area covered approximately 1100 km 9 locat-
ed in the metropolitan Milwaukee area in southeast Wis-
consin (43øN, 88øW). It included Milwaukee county and
parts of Waukesha, Washington, and Ozaukee counties.
Milwaukee and Ozaukee counties are bordered by Lake
Michigan to the east. Milwaukee county covers an area
of 626.5 km 9. The city of Milwaukee covers an area of
248.5 km 2 with a human population of 629 554 (1994
population estimate; 2533 people per km2). Human pop-
ulation density decreases radially from the city of Milwau-
kee to suburban communities and to rural areas. Two
•nterstate highways transect the study area. Land use
within the study area included agricultural, natural, in-
dustrial/commercial, and residential areas.
Red-tailed Hawk nests were located from a vehicle
from 1 February-30 April, 1987-94 (Craighead and
Craighead 1956) and visited at least twice (once within
10 d after the onset of incubation and again when nest-
hngs were 20-35 d of age) during each nesting season to
determine productivity (Postupalsky 1974, Steenhof
1987). Woodlots that were not entirely visible from the
road early in the season before leaf-out were checked by
foot. A breeding pair (i.e., eggs were laid) was considered
successful if -•1 nestling survived to a bandable age (20-
35 d). Intrayear internest distances for 1989 and 1990
were measured to determine the nearest breeding pair
of Red-tailed Hawks (nearest neighbor; Clark and Evans
1954). These data were used as an index for population
nesting density and to compare urban, suburban, and
rural densities (Clark and Evans 1954, McGovern and
McNurney 1986). We believe that all nests were found in
urban and suburban areas and, therefore, the distances
between nests in these locations are accurate.
To describe Red-tailed Hawk nesting habitat and to
compare urban, suburban, and rural locations, we char-
acterized feattires of 1989 and 1990 nest sites on four
different spatial scales: 1) nest site, 2) habitat, 3) mac-
rohabitat and 4) landscape (Titus and Mosher 1981, Mo-
sher et al. 1986, 1987, Adamus 1995, Stout 1995; Table
1). The nest-site scale described the nest and nest tree
and data were collected when nestlings were 20-35-d old
Nest exposure (i.e., the open side of the nest) was as-
signed one of the following values: total access/exposure,
N, NE, E, SE, S, SW, W, or NW. The nest tree was clas-
sified as being in a woodlot interior (the tree crown did
not touch a woodlot edge), on the edge of an interior
woodlot clearing (clearing was -•0.1 ha), savannah (not
on an edge), woodlot edge, hedgerow, lone tree, pow-
erline tower, or billboard.
The habitat scale described vegetation within a 0.04-ha
circular plot (11.3 m radius) centered on the nest tree
and data were collected after fledging through Septem-
ber for 1989 and 1990 nest sites. Canopy, understory,
shrub, ground cover, and slope of the plot were de-
scribed according to Titus and Mosher (1981) and Mo-
sher et al. (1986, 1987). Shrub structure was classified by
shrub density, shrub index and density board (Mosher et
al. 1986). Slope and slope aspect were determined for
sites with a slope -•2% using a compass and clinometer.
The landscape scale described land use within a 1.5-
km radius (706.9 ha) of the nest tree. Data were collected
for 1989 and 1990 nest sites, and used for analysis and
nest site classification (i.e., as urban, suburban, or rural).
The amount of land with natural, agricultural, residen-
tial, and industrial cover types within the landscape area
was determined from 1990 aerial photos (1 cm = 48 m)
with a compensating polar planimeter. The number of
individual areas of each cover type was recorded. Natural
habitat included woodlots, tree and shrub savannahs,
shrublands, herbaceous cover (grasses and forbs, fallow
fields, and inactive pasttires), and open water. The mean
area of open water was (1% (7 ha; maximum = 6.2%,
43.8 ha) and primarily consisted of pothole ponds and,
therefore, was included in the natural category. For man-
agement recommendations, natural habitat was subdivid-
ed into grassland and forest habitat. Agricultural land in-
cluded row crops (e.g., corn), cover crops (e.g., alfalfa
and clover), actively grazed pasttires, tree nurseries and
orchards. Residential land included human dwellings
and other buildings and land associated with them. In-
dustrial land included nonresidential industrial and com-
mercial buildings, pavement, roads, graded land (e.g,
gravel pits), mowed land (e.g., cemeteries, airports,
mowed land surrounding industrial buildings), and non-
mowed land associated with human activity (e.g., freeway
intersections, nonmowed land surrounding industrial
buildings). Each area was measured separately and com-
bined for analysis. Industrial and residential areas were
considered developed. Natural and agricultural areas
were considered undeveloped because they are devoid of
any buildings or pavement. A nest site was classified as
urban if >70% of the landscape area (706.9 ha) was de-
veloped, rural if --<30%, and suburban if 30-70% was de-
veloped (Stout et al. 1996). Hedgerow length was mea-
sured within the landscape area. The Baxter-Wolfe
interspersion index was determined from the changes in
cover type along the north-south and east-west median
lines within the landscape area (Baxter and Wolfe 1972,
Mosher et al. 1987). The area and perimeter ofwoodlots
containing nests were measured. Distances to the nearest
residence, industrial building and road were recorded
and mean distance to buildings was determined by using
a point-quarter method of measuring the distance to the
nearest building in each of four quadrants; a buffer area
(circular area surrounding the nest without buildings)
was calculated by using the mean distance to buildings
as the radius of a circle (Stout 1995). The macrohabitat
scale described land use within a 0.25 km radius (19.6
ha) of the nest for a comparison of land use patterns
closer to the nest site. The same variables that were mea-
sured at the landscape scale also were determined at the
macrohabitat scale.
Nest-site data were collected for all known breeding
pairs of Red-tailed Hawks in the metropolitan Milwaukee
area for 1989 and 1990. Nest sites that were used in both
1989 and 1990 (in either the same or a different nest
tree or structure) were included in the analysis only
once. Macrohabitat and landscape-scale data were col-
lected on all urban sites and at least as many suburban
and rural sites. According to our definitions, 15 urban
nest sites were found. For the urban, suburban, and rural
comparison, 22 suburban and 18 rural nest sites were
•dentified. Nest-site and habitat data were collected for
these sites where access (landowner permission) was
Categorical data were tested with a Chi-square good-
ness of fit. Urban, suburban, and rural nest sites were
compared using univariate statistics. Frequency distribu-
tions were used to determine variables with normal dis-
tributions. Log transformations were used when applica-
ble. Quantitative variables with normal distributions were
treated with parametric methods (one-way ANOVA). The
TUKEY multiple range test was used to identify different
groups. Nonparametric methods (Kruskal-Wallis test,
Chi-square approximation; Sokal and Rohlf 1981) were
used for nonparametric variables. All tests were consid-
ered significant when P--< 0.05. The Statistical Package
for the Social Sciences (SPSS; Nie et al. 1975) was used
for statistical analyses.
Productivity did not differ among urban, subur-
ban, and rural nest sites used by breeding Red-
tailed Hawks (Table 1). Mean nesting success for
Red-tailed Hawks in the Milwaukee metropolitan
area from 1989-94 (N = 426) was 81.9% (range =
75.3-92.7%; Table 2). Productivity of breeding
pairs for the same 6-yr period averaged 1.43
young/breeding pair (range = 1.13-1.91), and
1.75 young/successful nest (range = 1.61-2.06).
Productivity was significantly higher in 1994 than
each of the preceding years (P < 0.001). Mean in-
ternest distance for urban sites was greater than in
suburban and rural sites (P = 0.004, P < 0.001,
respectively), and mean internest distance was
greater for suburban than rural sites (P = 0.018;
Table 1).
In 1989 and 1990, we found 89 breeding Red-
tailed Hawks nesting in 18 species of trees. Four
were on high voltage transmission towers and one
was on a billboard. Nests constructed in trees and
on unnatural structures occurred in urban, sub-
urban, and rural areas (Stout 1995, Stout et al.
1996). Only one nest-site variable, nest-tree height,
was different for urban, suburban, and rural loca-
tions indicating behavioral consistency in nest
building (Stout 1995, Table 1). Nest structures
were in woodlots or on edges of woodlots more
often than in hedgerows, totally exposed lone
trees, or human-made structures (X 2 = 23.273, df
= 2, P < 0.001). Nests had a northwest exposure
more often than other directions (N = 88; Fig. 1;
X '• = 35.955, df = '8, P < 0.001). Sloped sites (N =
41) were not used more often than nonsloped sites
(N = 38; X • = 0.114, df = 1, P = 0.736). When
sloped, red-tails used a southeast slope more often
than other directions (Fig. 1; X = 19.293, df = 7,
P = 0.007).
At the habitat scale, the percent slope of plots
was greater for suburban sites than for rural sites,
the number of shrub species at suburban sites was
greater than at both urban and rural sites, and the
number of small understory saplings (dbh = 1-4
cm) at suburban sites was greater than at rural sites
(Table 1).
At the landscape scale, total hedgerow length
within the landscape area, mean building distance,
buffer area, nearest residence, industrial structure,
building, road, the Baxter-Wolfe interspersion in-
dex, and the amount of natural, agricultural, in-
dustrial and residential land were different for ur-
ban, suburban, and rural sites (Table 1). At the
macrohabitat scale, agricultural, industrial, and res-
idential land use were different, but the amount of
natural cover (total grassland and forest cover) did
not differ among the three sites (Table 1). Natural
cover within the macrohabitat area averaged 10.3
ha for all three locations while natural habitat with-
in the larger landscape area averaged 111.3 ha
224 STOUT ET AL. VOL. 32, NO. 3
Table 1. Comparison of productivity, nest site, habitat (0.04-ha circular plot, 11.3-m radius), macrohabitat (19.6-ha,
0.25-km radius) and landscape (706.9 ha, 1.5 km radius) for urban, suburban and rural Red-tailed Hawk nest sites.
Nest site and habitat results do not include nests on artificial substrates. Productivity, macrohabitat and landscape
results include nests on artificial substrates.
Productivity 1.27 - 0.25 1.50 +__ 0.19 1.44 _ 0.22 0.593 c 0.744
0-3 (15) 0-3 (22) 0-3 (18)
Nest Site
Nest tree height (m) 20.09 - 1.00 x 23.33 ----- 0.67Y 21.09 ----- 0.99 xy 3.699 b 0.033
14.10-26.30 (11) 18.50-28.96 (20) 14.17-28.65 (16)
Habitat (0.04-ha circular plot, 11.3-m radius)
% Slope 2.7 -4- 1.75xy 3.6 -4- 0.86 x 1.0 + 0.46Y 6.076 c 0.048
0-10 (7) 0-16 (21) 0-6 (15)
No. shrub species 4.6 _ 0.95 x 7.4 ----- 0.56Y 4.5 ----- 0.84 x 5.640 b 0.007
1-8 (7) 4-12 (21) 0-11 (15)
No. small saplings 48.3 __+ 9.61xy 72.6 --- 8.67 x 40.9 _+ 9.32Y 6.420 c 0.040
0-78 (7) 15-183 (21) 0-113 (15)
Macrohabitat Area (19.6-ha, 0.25-km radius)
Grassland (ha) 4.77 ___ 1.38 4.37 +__ 0.76 4.53 +_ 1.34 0.143 ½ 0.813
0.0-17.2 (15) 0.0-13.3 (22) 0.0-18.5 (18)
Forest (ha) 4.83 4-_ 1.19 6.06 ___ 0.72 5.91 __+ 1.05 1.528 ½ 0.466
0.0-13.3 (15) 0.0-15.2 (22) 0.3-14.1 (18)
Natural (ha) 9.76 4-_ 1.68 10.62 - 0.97 10.44 _ 1.49 0.067 ½ 0.967
0.0-17.7 (15) 2.6-18.8 (22) 1.3-19.6 (18)
Agricultural (ha) 0.17 ___ 0.17 x 3.89 ----- 1.05Y 7.76 --+ 1.53 z 21.17F <0.001
0.0-2.6 (15) 0.0-15.6 (22) 0.0-18.2 (18)
Industrial (ha) 5.24 -+ 1.68 x 3.14 ___ 0.96 x 0.46 -4- 0.25Y 10.263 c 0.006
0.0-18.9 (15) 0.0-16.2 (22) 0.0-3.5 (18)
Residential (ha) 4.43 +__ 1.16 x 1.96 +__ 0.56Y 0.93 + 0.45Y 15.160 0.001
0.7-19.0 (15) 0.0-9.1 (22) 0.0-6.4 (18)
Woodlot area a (ha) 9.93 __+ 4.19 8.53 4- 1.27 9.39 --- 2.99 0.164 b 0.850
0.3-45.4 (11) 2.5-20.2 (20) 0.3-39.5 (15)
Woodlot perimeter a (m) 1550 - 403.0 1425 - 137.0 1715 4- 440.9 0.348 b 0.708
288-3936 (11) 768-2688 (20) 307-6816 (15)
Mean building dis. (m) 224 - 17.7 x 322 --- 35.4Y 455 __+ 29.9 z 12.607 b <0.001
68-341 (15) 79-759 (22) 150-692 (18)
Buffer area a (ha) 17.10 + 2.35 x 40.89 __+ 8.85 x 62.18 ___ 7.27Y 9.004 b <0.001
1.5-36.5 (15) 2.0-181.0 (22) 7.1-127.5 (18)
Nearest residence a (m) 117 ___ 10.6 x 240 + 26.1Y 289 _+ 34.3Y 11.327 b <0.001
30-178 (15) 86-533 (22) 67-571 (18)
Nearest industry (m) 348 +_ 69.8 x 397 ___ 72.1 x 743 __+ 97.2Y 6.915 b 0.002
48-1080 (15) 62-1166 (22) 187-1375 (17)
Nearest building a (m) 106 +__ 11.3 x 180 -4- 15.0Y 272 -- 33.0 z 12.620 b <0.001
30-178 (15) 62-293 (22) 67-571 (18)
Nearest road a (m) 114 ___ 14.9 x 218 -4- 28.5Y 322 4- 48.5Y 8.292 b 0.001
24-197 (15) 53-518 (22) 38-878 (18)
Mean internest dis. a (m) 2743 4- 319.3 x 1780 + 120.9Y 1316 +--- 165.5 z 11.322 b <0.001
1327-4968 (15) 799-2904 (20) 403-2246 (15)
Table 1. Continued.
Landscape Area (706.9-ya, 1.5-km radius)
Baxter-Wolfe Index 18.3 _+ 1.36 x
8-27 (15)
Hedgerow length (m) 7619 _+ 1087 X
2208-16080 (15)
Grassland (ha) 67.20 --- 11.14 X
0.0-146.3 (15)
Forest (ha) 39.30 _ 6.26 x
0.0-94.0 (15)
Natural (ha) 111.27 _+ 13.52 x
16.3-190.2 (15)
Agricultural (ha) 11.69 ñ 4.05 x
0.0-48.8 (15)
Industrial (ha) 273.85 _+ 35.34 x
56.6-499.1 (15)
Residential a (ha) 310.00 _ 31.28 x
153.4-537.2 (15)
28.8 -+ 1.03Y 26.2 -+ 1.26 z 19.304 b <0.001
21-40 (21) 19-37 (18)
10506 +__ 995xy 12 053 m 981Y 4.258 b 0.019
1920-18 432 (22) 3984-18 720 (18)
137.23 _+ 8.57Y 141.18 _ 22.77Y 6.707 b 0.003
70.0-231.9 (22) 24.7-312.5 (18)
77.82 ___ 7.56Y 103.80 _+_ 9.70 z 14.007 b <0.001
31.1-178.9 (22) 43.1-187.3 (18)
221.07 + 10.68Y 253.11 +_ 29.22Y 13.166 b <0.001
123.7-329.4 (22) 81.3-457.4 (18)
128.05 - 14.75Y 309.74 m 30.76' 40.587 c <0.001
20.5-310.3 (22) 108.2-534.4 (18)
180.45 +_ 18.94Y 53.57 -+ 9.77 z 23.117 u <0.001
39.6-354.2 (22) 0.0-123.0 (18)
177.27 -+ 15.65Y 90.68 - 9.60 z 25.905 b <0.001
21.9-331.5 (22) 25.5-173.2 (18)
Variables log-transformed for one-way Analysis of Variance (one-way ANOVA).
One-way ANOVA F values.
Kruskal-Wallis test X 2 values (X 2 approximation).
x• Values followed by the same superscript letter x, y or z, are not significantly different at the P -< 0.05 level (TUKEY multiple range
test b or Mann-Whitney U testC).
(15.7%) for urban nest sites only, and this natural
habitat was interspersed among developed land in
an average of 16.4 different tracts.
Reproductive success and productivity of breed-
ing Red-tailed Hawks during our 6-yr study was
comparable to that of previous studies in Wiscon-
sin (Orians and Kuhlman 1956, Gates 1972, Peter-
son 1979; Table 2) and an urban/suburban area
in New York (Minor et al. 1993). Red-tailed Hawk
nest success estimates for North America range
from 58-93% (Preston and Beane 1993).
The distance between breeding pairs of Red-
tailed Hawks was used as an index of nesting den-
sity (McGovern and McNurney 1986). Our mean
internest distance of 1.9 km was comparable to
other studies (Fitch et al. 1946, Orians and Kuhl-
man 1956, Gates 1972, Petersen 1979, McGovern
and McNurney 1986). Rural nests were significant-
ly closer together than suburban and urban nests,
and suburban nests were closer together than 'ur-
ban nests which indicated that nesting density de-
creased from rural to urban areas. We found rural
nests adjacent to suburban nests at the perimeter
of our study area. As a result, the nearest breeding
pair of red-tails may not have been found in all
rural areas making rural nests even closer than our
data indicated. Peterson (1979) found a mean in-
ternest distance of 1.51 km in rural Wisconsin. Our
mean internest distance of 1.32 km between rural
nests may indicate that the density of nesting Red-
tailed Hawks may have increased in rural southeast
Wisconsin over the past 25 yr, possibly because of
increased availability of nesting habitat resulting
from changes in agricultural practices such as the
conservation reserve program (CRP).
The microclimate surrounding nest structures is
important in the selection of nest sites by raptors.
We found Red-tailed Hawk nests had predomi-
nantly northern exposures (primarily NW and NE)
and sloped sites had southeast aspects. Speiser and
Bosakowski (1988) also found Red-tailed Hawk
nests to have southeast facing slope exposures.
They suggested that a southeast slope maximizes
insulation to the nest on cold mornings and min-
226 STOUT ET AL. VOL. 32, No. 3
Table 2.
Red-tailed Hawk reproductive success from 1989-94 for the metropolitan Milwaukee, Wisconsin area.
P•d}•S F•dLURES SUCCESS (%) 1 2 3 A a B b
1989 59 11 81.4 20 24 4 1.36 1.67
1990 85 21 75.3 19 39 6 1.35 1.80
1991 92 16 82.6 33 40 3 1.33 1.61
1992 83 9 89.2 24 45 5 1.55 1.74
1993 52 16 69.2 16 17 3 1.13 1.64
1994 55 4 92.7 13 22 16 1.91 2.06
Total 426 77 81.9 125 187 37 1.43 1.75
Young/breeding pain
Young/successful nest.
imizes the possibility of heat stress in the after-
noon. Southeast slopes may help to keep nestlings
dry by minimizing the effects of predominantly
northwest storm winds in Wisconsin while north-
ern nest accesses may provide more shade and re-
duce heat stress. Several studies also found that
nest sites usually have unobstructed access and a
commanding view of the surrounding area (Peter-
sen 1979, Bednarz and Dinsmore 1982, Santana et
al. 1986, Speiser and Bosakowski 1988, Bechard et
al. 1990, Toland 1990, Preston and Beane 1993).
Sloped nest sites probably provide this type of nest
Red-wiled Hawks used similar types of nest sites
in urban, suburban, and rural locations, however,
suburban nest sites tended to be located on sloped
sites and in wetlands, probably because upland
sites are developed first. Suburban areas also had
the highest land use diversity (Baxter-Wolfe inter-
spersion index) while urban locations had the least
amount of land use diversity. Woodlot area and pe-
rimeter remained relatively constant for urban,
Nest Slope
Exposure Aspect
N-6 N-2
NW-22 V NE-19 NW-5 I NEE'9
W-7 E-3 W-1 -- E-2
SW-8 SE-7 SW-5 -12
S-12 S-5
Fzgure 1. Nest exposure (N = 84) and slope aspect (N
= 41) at Red-tailed Hawk nest sites in southeast Wiscon-
sin. Sample size is indicated for each direction.
suburban, and rural nesting locations indicating
that 9 ha may represent an ideal size woodlot for
Red-wiled Hawk nesting sites. Other studies have
found that red-tails selected smaller woodlots,
open stands, and woodlot edges compared to larg-
er woodlots or closed canopy woodlot interiors
(Orians and Kuhlman 1956, Gates 1972, Petersen
1979). Speiser and Bosakowski (1988) found that
red-wils nested closer to forest openings than ran-
dom sites and Howell et al. (1978) reported that
the most productive pairs of Red-tailed Hawks used
small woodlots.
Landscape variables (e.g., nearest road, industry,
residence) varied significantly and increased from
urban to suburban and rural areas. The amount of
natural and agricultural land within the landscape
scale decreased as the amount of industrial and
residential land increased. While the amount of ag-
ricultural land increased and residential and in-
dustrial land decreased at the macrohabitat scale
from rural through suburban and urban areas, the
amount of natural cover within the macrohabitat
remained consistent for all three areas averaging
10.3 ha indicating that natural cover constitutes an
important nesting habitat component for Red-
wiled Hawks.
For the purposes of urban planning and devel-
opment, we believe that managing for important
habitat components such as natural cover will en-
hance the availability of nesting habitat for Red-
tailed Hawks in urban areas. Based on our find-
ings, we recommend that at least 16% of urban
land be left in natural habitat with approximately
40% wooded and 60% herbaceous cover. This nat-
ural habitat should be distributed among residen-
tial and industrial land in approximately 16 sepa-
rate tracts within the landscape area (706.9 ha).
Wooded areas should be approximately 9 ha to
provide suitable nesting woodlots.
J.W. Hardin and R.W. Miller provided guidance and
editorial assistance. D. Hebbert helped collect nest site
and habitat data. R.D. Beane, S. Postupalsky, K. Titus and
two anonymous reviewers provided comments and sug-
gestions that greatly improved this manuscript. J.A. Rei-
hartz and R. Rogers provided assistance with statistical
analyses. The senior author's wife, Vicki, daughter, Jen-
nifer, and son, Tim, provided continual support, patience
and assistance in all areas of this research project. This
project was partially funded by the U.W.-Stevens Point
Graduate School Student Research Fund, and V.W. De-
broux. An earlier version of this manuscript was submit-
ted to the University of Wisconsin-Stevens Point, College
of Natural Resources, in April 1995 for partial fulfillment
of a Master of Science degree in Natural Resources
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Received 21 November 1997; accepted 19 May 1998
... For example, members of a guild may be migratory or sedentary, diurnal or nocturnal, colonial or territorial or consume vertebrates or arthropods (Doná zar et al. 2016). Raptor reproductive rates, specifically, serve as an index for habitat quality and fitness (Stout, Temple, and Papp 2006;Millsap 2018), and are easier to assess than for more elusive predators (Steenhof and Newton 2007). ...
... We used four metrics to model urban density: number of residents (based on the Washoe County per person household multiplier of 2.56), number of employees, building footprint area and building height (based on floor count) for each land parcel (White et al. 2018b). The density of each metric was calculated within four radii around each nest at four spatial resolutions: 11.3 m (nest-site scale, 1-m 2 resolution; Stout, Anderson, and Papp 1998); 250 m (macrohabitat scale, 2-m 2 resolution); 740 m [average intraspecific, nearest-nest midpoint scale (henceforth nearest nest scale), 4-m 2 resolution; Gilmer and Stewart 1983]; and 1500 m (landscape scale, 4-m 2 resolution; Tapia and Zuberogoitia 2018). Density values for each metric were rescaled to be equally weighted, summed with the other metrics across spatial scales, and rescaled again to values 0-1, with 1 being the most urban, to produce an index of the urban gradient (White et al. 2018b). ...
... Nests occupied for !20 incubation days were included in analyses. We used GLMs to relate nesting success, productivity and fledge rate to combinations of urban density and habitat type at the nest-site, macrohabitat, nearest nest, landscape scales and hatch date (Newton and Marquiss 1984;Steenhof et al. 2017). Hatch date was also included as a response variable and related to combinations of urban density and habitat type. ...
Full-text available
Despite the unique threats to wildlife in urban areas, many raptors have established successfully reproducing urban populations. To identify variations in raptor breeding ecology within an urban area, we compared metrics of Red-tailed Hawk reproductive attempts to landscape characteristics in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. We used the Apparent Nesting Success and logistic exposure methods to measure nesting success of the Red-tailed Hawks. We used generalized linear models to relate nesting success and fledge rate to habitat type, productivity to hatch date (Julian day) and hatch date to urban density. Nesting success was 86% and 83% for the respective years. Nesting success increased in grassland-agricultural and shrub habitats and decreased in riparian habitat within the urban landscape. Productivity was 2.23 and 2.03 per nest for the breeding seasons. Fledge rates were 72% and 77%, respectively, and decreased in riparian areas. Nestlings hatched earlier with increased urban density and earliest in suburban areas, following a negative quadratic curve. Nesting success and productivity for this population were high relative to others in North America. Productivity increased in habitats where ground prey was more accessible. We suggest that suburban areas, if not frequently disturbed, provide sufficient resources to sustain Red-tailed Hawks over extended periods. As urban expansion continues in arid environments globally, we stress that researchers monitor reproductive output across the urban predator guild to elucidate patterns in population dynamics and adaptation.
... 35 Unsurprisingly, urban raptors' nesting areas were closer to houses and roads than their counterparts' in rural areas. 30,36,37 Other than these measures, suburban nest sites of some species, such as red-shouldered hawks, differed little from rural ones. 36 But in other species, the nest trees and nesting areas differed in interesting ways. ...
... 30 Suburban red-tailed hawks' nest trees were taller than urban and rural nest trees, and suburban plots around nests had more species of shrubs and more saplings than urban and rural sites. 37 On a landscape scale, urban raptors tend to select areas with more natural land-cover types. For example, urban and suburban red-tailed hawks avoided the areas of densest urban cover and selected areas with more grassland, more forest, and greater land-cover diversity compared to unused plots. ...
Raptors are an unusual success story of wildness thriving in the heart of our cities—they have developed substantial populations around the world in recent decades. But there are deeper issues around how these birds make their urban homes. New research provides insight into the role of raptors as vital members of the urban ecosystem and future opportunities for protection, management, and environmental education. A cutting-edge synthesis of over two decades of scientific research, Urban Raptors is the first book to offer a complete overview of urban ecosystems in the context of bird-of-prey ecology and conservation. This comprehensive volume examines urban environments, explains why some species adapt to urban areas but others do not, and introduces modern research tools to help in the study of urban raptors. It also delves into climate change adaptation, human-wildlife conflict, and the unique risks birds of prey face in urban areas before concluding with real-world wildlife management case studies and suggestions for future research and conservation efforts. Boal and Dykstra have compiled the go-to single source of information on urban birds of prey. Among researchers, urban green space planners, wildlife management agencies, birders, and informed citizens alike, Urban Raptors will foster a greater understanding of birds of prey and an increased willingness to accommodate them as important members, not intruders, of our cities.
... 35 Unsurprisingly, urban raptors' nesting areas were closer to houses and roads than their counterparts' in rural areas. 30,36,37 Other than these measures, suburban nest sites of some species, such as red-shouldered hawks, differed little from rural ones. 36 But in other species, the nest trees and nesting areas differed in interesting ways. ...
... 30 Suburban red-tailed hawks' nest trees were taller than urban and rural nest trees, and suburban plots around nests had more species of shrubs and more saplings than urban and rural sites. 37 On a landscape scale, urban raptors tend to select areas with more natural land-cover types. For example, urban and suburban red-tailed hawks avoided the areas of densest urban cover and selected areas with more grassland, more forest, and greater land-cover diversity compared to unused plots. ...
If there is a single unifying characteristic of urban/suburban wildlife species, it is likely adaptability. Species that can occupy urban areas are behaviorally flexible,1,2 and this flexibility drives changes in the way they use urban space and cohabit with people. Raptors too exhibit behavioral changes when they move from rural to urban environs.³ Inherent plasticity allows some raptors to adjust their behavior to survive in circumstances that may differ greatly from those of more typical, rural, or natural areas. For example, they may move into urban environments that are suitable for them,4,5 or they may persist by tolerating human activity in a natural area that has been overwhelmed by suburbia. They may perceive human-made objects such as rooftops, utility towers, billboards, and bridges as potential nest sites,3,6,7,8 especially in areas where nest sites in traditional, natural locations are limited. Additionally, they may take advantage of a different prey type that is present, such as rats (Rattus spp.),9,10 or a typical prey type that is more abundant or available (e.g., birds at feeders).5,11
... The habitat and dietary generalism of many raptors, as well as the attractiveness of diverse land cover types and habitat fragmentation in cities to raptors, are generally well studied, but the implications of urbanization for the breeding ecology of raptors are less understood (Stout et al. 1998(Stout et al. , 2006aChace and Walsh 2006;Hager 2009). Therefore we aim to identify the specific urban density level where raptors nest. ...
... Density surfaces were created at four spatial scales around the nest and at varying resolutions: 1-m 2 resolution for the nest site scale (11.3-m radius around the nest), 2m 2 resolution for the macrohabitat scale (250-m radius), and 4-m 2 resolution for both the average intraspecific, nearestnest scale (670-m radius; excluding Golden Eagles) and the landscape scale (1500-m radius; Fig. 2). These spatial scales were selected based on the methods of Gilmer and Stewart (1983) and Stout et al. (1998). We rescaled the data to values of 0-1 weighting the metrics equally and then summed the four metrics across the four scales for an index of urbanness. ...
Full-text available
Raptors are the most prevalent group of urban apex predators, and the majority of raptor genera in North America have been recorded using urban areas. Prior research assessments along urban-wildland gradients show that urban habitat preference varies by raptor species and that raptor nesting preferences within urban settings may vary. Attempts to understand the intra- and inter-specific nesting patterns along an urban gradient would advance extant knowledge. Here we present the locations of individual nest sites of nine raptor species along an urban gradient in Reno-Sparks, NV. We developed an urban density model based on the number of residents, number of employees, and building footprints and number of floors for built structures within each land parcel at four spatial scales, representing nest site, macrohabitat, average nearest-nest, and landscape scales. Cooper’s Hawks (Accipiter cooperii), Sharp-shinned Hawks (Accipiter striatus), and Red-tailed Hawks (Buteo jamaicensis) nested across the widest range of the urban spectrum and closest to the urban core, whereas Golden Eagles (Aquila chrysaetos) and Swainson’s Hawks (Buteo swainsonii) nested on the urban fringe. Urban density for all nest locations was lowest at the nest-site scale, and the highest at the average nearest-nest and landscape scales. Raptors tended to occupy a wide range of the building-area density spectrum but not the building-height or employee density spectrums indicative of the attractiveness of suburban habitat.
... Raptor responses to urbanization varies from having enhanced reproductive success (Botelho and Arrowood 1996;Gehlbach 1996;Parker 1996;Stout et al. 2006;Rebolo-Ifrán et al. 2017;Welch-Acosta et al. 2019), to showing a neutral response (Stout et al. 1998;Millsap et al. 2004;Kübler et al. 2005;Dykstra et al. 2009;Rose et al. 2017) or experiencing negative effects during breeding (Tella et al. 1996;Bond et al. 2005;Sumasgutner 2013;Sumasgutner et al. 2014a). Raptor species that respond well to urban mosaic landscapes usually expand their range into urban and suburban areas (Carrete et al. 2009). ...
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Urban sprawl is recognized to homogenize biota, with several species that fail to adapt to these new human scenarios. However, some species can live and breed successfully in urbanized habitats. We compared the breeding performance of the relatively common raptor and poorly studied, chimango caracara (Milvago chimango) in an urban gradient of central Argentina. Breeding data of 359 nests were collected during breeding seasons from 2010 to 2012. Birds nested in colonies of 3 – 75 pairs. Overall breeding success was 49.9% with productivity at 1 ± 1.14 chicks per nest. Models revealed that reproductive success and productivity were higher in nests with earlier laying dates and sited in larger colonies and that urbanization gradient did not affect either reproductive output or laying day. Urban habitats in central Argentina appear to provide similar reproductive success of chimango caracara than rural or natural habitats. Thus, chimango caracara shows behavioral plasticity for their successful persistence to human changes as reflected in successfully breeding in a wide variety of habitats such as natural, rural, and urbanized environments that have been impacted by humans.
... Building height and footprint allowed us to account for building volume. Urban density was calculated at four spatial resolutions and scales based on spatial requirements of raptors elsewhere and the inter-nest distance in our area: 1 m 2 resolution for the nest-site scale (within an 11.3 m radius around the nest), 2 m 2 resolution for the macrohabitat scale (250 m radius) and 4 m 2 resolution for the average intraspecific, nearest-nest midpoint scale (740 m radius; referred to as the nearest nest scale from here on) and the landscape scale (1500 m radius; Gilmer and Stewart 1983;Stout, Anderson and Papp 1998). Urban density was rescaled to values between 0.00 and 1.00, with 1.00 representing the most urban, to produce an index of 'urbanness' (White et al. 2018a). ...
We examined Red-tailed Hawk (Buteo jamaicensis) nestling diets in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. Field researchers and nest cameras recorded 1348 prey items spanning 28 species at 88 nests. Prey consisted of 86% mammalia, 10% aves and 4% reptilia. Differential prey selection occurred among the population and at individual nests relative to an expected diet. Diet breadth differed between nests and increased with urban density. Avian prey consumption increased relative to mammalian and reptilian prey in impervious areas. When prey items were plotted on a continuous urban density spectrum, mammalian prey increased in the suburban areas and decreased toward the urban core and was inversely correlated with avian prey. Mammalian prey consumption increased and decreased at the end of April and in mid-May before increasing through the remainder of the breeding season (mid-June). Avian prey consumption peaked in May and increased through the season, and reptilian prey varied little. The geographic patterns of prey species consumed in our study reflect those in cities elsewhere. As the urban area changes, we predict that the densest populations of Red-tailed Hawks will continue to reside in the suburban areas where prey diversity and abundance are highest. This was one of the first studies to record urban Red-tailed Hawk diet and revealed patterns in how an urban population used food resources.
... Four observations were removed because they reported a SD of zero (these indeed had very low sample sizes: 3, 2, 7, 2 observations). Our final dataset included 399 comparisons between paired urban-non-urban populations from 35 bird species and 68 studies (Figure 1; refs.: Antonov & Atanasova, 2003;Bailly et al., 2016;Baldan & Ouyang, 2020;Beck & Heinsohn, 2006;Berardelli et al., 2010;Biard et al., 2017;Boal & Mannan, 1999;Bobek et al., 2018;Brahmia et al., 2013;Caizergues et al., 2018;Capilla-Lasheras et al., 2017;Cardilini et al., 2013;Charter et al., 2007;Conway et al., 2006;de Satgé et al., 2019;Dhondt et al., 1984;Eden, 1985;Evans & Gawlik, 2020;Gahbauer et al., 2015;Glądalski, Bańbura, Kaliński, Markowski, Skwarska, Wawrzyniak, Zieliński, & Bańbura, 2016;Glądalski, Bańbura, Kaliński, Markowski, Skwarska, Wawrzyniak, Zieliński, Cyżewska, & Bańbura, 2016;Glądalski et al., 2015Glądalski et al., , 2017Glądalski et al., , 2018Gryz & Krauze-Gryz, 2018;Hajdasz et al., 2019;Hinsley et al., 2008;Ibáñez-Álamo & Soler, 2010;Isaksson et al., 2008;Isaksson & Andersson, 2007;Jarrett et al., 2020;Kelleher & O'Halloran, 2007;Kettel et al., 2019;Kopij, 2017;Lee et al., 2017;Lin et al., 2015;Liven-Schulman et al., 2004;Luna et al., 2020;Mcgowan, 2001;Mennechez & Clergeau, 2006;Middleton, 1979;Millsap et al., 2004;Minias, 2016;Morrissey et al., 2014;Newhouse et al., 2008;Partecke et al., 2020;Perlut et al., 2016;Pollock et al., 2017;Preiszner et al., 2017;Rollinson & Jones, 2003;Rosenfield et al., 2019;Schmidt & Steinbach, 1983;Schoech et al., 2007;Schoech & Bowman, 2001;Seress et al., 2012Seress et al., , 2018Seress et al., , 2020Sharma et al., 2004;Shustack & Rodewald, 2011;Solonen, 2001Solonen, , 2014Solonen & Ursin, 2008;Stout et al., 1998;Stracey & Robinson, 2012;Sumasgutner et al., 2014;Thornton et al., 2017;Wawyrzyniak et al., 2015;Welch-Acosta et al., 2019). Of these 399 comparisons, 151 corresponded to comparisons of laying date (n = 32 studies), 119 were comparisons of clutch size (n = 42 studies) and 129 were comparisons of number of fledglings (n = 48 studies) ( Figure S2). ...
Full-text available
Cities pose a major ecological challenge for wildlife worldwide. Phenotypic variation, which can result from underlying genetic variation or plasticity, is an important metric to understand eco‐evolutionary responses to environmental change. Recent work suggests that urban populations might have higher levels of phenotypic variation than non‐urban counterparts. This prediction, however, has never been tested across species nor over a broad geographical range. Here, we conducted a meta‐analysis of the avian literature to compare urban versus non‐urban means and variation in phenology (i.e. lay date) and reproductive effort (i.e. clutch size, number of fledglings). First, we show that urban populations reproduce earlier and have smaller broods than non‐urban conspecifics. Second, we show that urban populations have higher phenotypic variation in laying date than non‐urban populations. This result arises from differences between populations within breeding seasons, conceivably due to higher landscape heterogeneity in urban habitats. These findings reveal a novel effect of urbanisation on animal life histories with potential implications for species adaptation to urban environments (which will require further investigation). The higher variation in phenology in birds subjected to urban disturbance could result from plastic responses to a heterogeneous environment, or from higher genetic variation in phenology, possibly linked to higher evolutionary potential.
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Cities in general possess limited areas of original vegetation, or even artificial green areas; this results in drastic modification of faunal communities, with reductions in their original abundance and diversity. Nevertheless, some species are able to thrive in cities, including high trophic level species such as raptors. The object of this study was to characterise the diversity, abundance and reproduction of diurnal and nocturnal raptors in the urban area of a city in southern Chile. Twelve species of raptor were recorded, seven diurnal and five nocturnal. The species recorded most frequently were Coragyps atratus and Glaucidium nanum ; the least frequent species were Parabuteo unicinctus and Elanus leucurus. Eighteen nesting sites were recorded of six species of diurnal and nocturnal raptors: Falco sparverius , Milvago chimango , G. nanum , Strix rufipes , Tyto alba and Athene cunicularia . This is a good sample of the diversity of raptor species which reside permanently in urban areas.
Increasing human populations have accelerated urbanization and altered natural habitats. This process began in the eighteenth century with the industrial revolution when workers began moving to cities leaving agricultural jobs for jobs in manufacturing. Global growth in human populations was accompanied by growth of cities, which has increased the demand of goods and services provided by the exploitation of natural ecosystems. Rapid worldwide urbanization has led to a rampant loss of natural habitats and habitat fragmentation, which alarmed to ecologists and conservationists that have focused their researches in last years to understand the response of wildlife to these new scenes. For birds, the number of published studies on urban effects has increased steadily (Marzluff et al. 2001; Marzluff 2017). However, raptors have been poorly studied during much years, mainly due to several limitations imposed by their natural history (i.e., low densities, large home ranges, variable reproductive behaviors, and inaccessible breeding sites) (Donázar et al. 2016) and the high costs necessary for these studies. Nowadays, research of raptors in urbanized habitats has increased considerably. We will focus on a variety of these aspects.
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I documented two relatively early successful Great Horned Owl nesting attempts for the 2008 breeding season; one of these is the earliest documented nesting attempt in a breeding season for the state of Wisconsin with a clutch initiation date of 29 December 2007. Both nesting attempts were in the Oak Creek Township of Milwaukee County and were in enclosed microclimates. The protected, relatively warm nest microclimates of these two sites may have encouraged these adults to lay eggs early. The average clutch initiation date for the earliest nest site from 2003–2008, which was successful every year, was 7 January, one month (31 days) earlier than the average clutch initiation date for other Great Horned Owl nesting attempts for this study from 2002–2005. Nevertheless, as populations increase, Great Horned Owls may adapt to new environs or become more tolerant of the extremes of their breeding limits, including temperature.
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ABSTRACT. Raptors commonly nest on powerline towers in the western United States (U.S.). This phenomenon usually occurs on open plains, prairie or savannah, and is attributed to the absence of suitable natural nest sites. In the eastern U.S., Red-tailed Hawks (Buteo jamaicensis) nest predominantly in deciduous trees and less frequently in evergreens, and in southeast Wisconsin almost exclusively in deciduous trees. Red-tailed Hawks will nest on man-made structures in the eastern U.S. However, there is only one published report of two successful nests on power poles in Polk County, Florida. We documented 15 successful Red-tailed Hawk nests in 4 yr on five man-made structures in southeast Wisconsin, and compared them to nests on natural substrates. Four structures were high voltage transmission towers (three different structure types), and one was a billboard. The use of man-made structures for nest substrates may be a local occurrence, and may be related to growing urban populations of Red-tailed Hawks in locations such as Milwaukee. Keywords for indexing: Red-tailed Hawk, powerline, billboard, urban, suburban, rural
A new avian richness evaluation method (AREM) was developed and tested for assessing lowland wetland and riparian habitats of the Colorado Plateau. AREM rapidly scores habitats for avian richness from simple observations of habitat characteristics. AREM's predictions were compared with original field data from 76 sites on the Colorado Plateau during the breeding season. Species predictions and detections were highly indicative of the breeding avifauna in regional wetlands studied. -from Author
Some forty years ago, the concept of habitat interspersion was advanced by Aldo Leopold (1931). Indicating then that "we are only on the threshold of an understanding of the ecology of game species," Leopold went on to postulate his law of interspersion which recognized that “game is a phenomenon of edges.” Although the validity of Leopold's premises has been documented both directly and indirectly many times in the past four decades, the complexity and frustration in describing ecological diversity of game range has continued to pose a problem for wildlife managers since 1931.
Road counts of the Red-tailed Hawk in the eastern one-third of Kansas indicated a breeding population density of one per 16.5 km2 (one nest per 37 km2). Counts in winter indicated a population density 1.4 to 2.2 times as great. Most nests were in American elms, cottonwoods and sycamores in that order of preference but fifteen other species of trees were used for nest sites. Average height of all nests was 13.3 m and successful nests averaged slightly higher than those that failed. Of 195 nesting attempts, 126 failed; approximately two-thirds of the failures were caused by weather, mainly high winds. The 69 nests that fledged young had 25 percent mortality of nestlings. In 10 of 18 instances of predation, the raccoon was the predator implicated. Among forty prey items identified at nests and 2720 identified from pellets picked up under nests, the prairie vole was most frequent, the black rat snake second and the Eastern cottontail third. In terms of biomass, Eastern cottontail, black rat snake and prairie vole, in that order, were the principal prey species (90 percent), with many other kinds of small mammals, lizards and snakes (and a few birds and insects) each making up relatively small parts of the total.