Journal of Mammalogy, 88(4):1090–1097, 2007
HABITAT USE BY INTRODUCED RACCOONS AND NATIVE
RACCOON DOGS IN A DECIDUOUS FOREST OF JAPAN
FUMIE OKABE*
AND
NAOKI AGETSUMA
Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan (FO)
Tomakomai Experimental Forest, Field Science Center for Northern Biosphere, Hokkaido University, Takaoka,
Tomakomai, Hokkaido 053-0035, Japan (NA)
We investigated habitat use by introduced raccoons (Procyon lotor) and native raccoon dogs (Nyctereutes
procyonoides albus) in a northern deciduous forest of Japan to examine the relationship between the 2 species.
Spatial and temporal habitat use in the forest was monitored using infrared-triggered cameras. We also surveyed
environmental factors at 2 spatial scales: at the macrohabitat scale, we examined forest growth stage, forest
fragmentation, and distance from a water source; at the microhabitat scale, we examined forest structure,
understory vegetation, and beetle abundance. We then analyzed the relationship between environmental factors
and habitat use by each species using generalized linear model. Except for fern coverage, most environmental
factors at the micro- and macrohabitat scales had different effects on the habitat use of these species. Moreover,
the degree of diurnal activity also differed between the species. These spatial and temporal differences in habitat
use between raccoons and raccoon dogs provide further evidence that competition between these 2 species may
be limited in this area.
Key words: alien species, competition, habitat use, Japan, Nyctereutes procyonoides, Procyon lotor, raccoon, raccoon dog,
spatial scale
Niche partitioning has often been cited as a mechanism to
reduce competition and achieve the coexistence of multiple
species in the same habitat (e.g., MacArthur 1958; Pianka 1978;
Rosenzweig 1966). Niche partitioning develops through interactions among species during their evolutionary history (e.g.,
Krebs 2001; Polis and Myers 1989; Schoener 1982). Thus,
sympatric species generally exhibit some differences in food
habits, habitat preferences, periods of activity, or a combination of
these (Lack 1971; Schoener 1974). However, niche partitioning is
not expected to occur between alien and native species because
they do not have the history of interactions required for its
establishment. This is one reason why alien species can have
strong negative effects on native species (e.g., Murakami and
Washitani 2002; Nakano and Taniguchi 1996; Primack and
Kobori 1997; Schlaepfer et al. 2005). In serious cases, alien
species will eliminate or reduce the numbers of native species
(Herbold and Moyle 1986; Usher et al. 1992; World Conservation
Union Council [IUCN], Guidelines for the prevention of
biodiversity loss caused by alien invasive species, http://www.
iucn.org/themes/ssc/publications/policy/invasivesEng.htm).
* Correspondent: [email protected]
Ó 2007 American Society of Mammalogists
www.mammalogy.org
1090
Raccoons (Procyon lotor) are medium-sized carnivores that
were introduced to Japan from North America in the early
1960s (Agetsuma-Yanagihara 2004). Wild populations became
established in Japan in the 1970s (Ando and Kajiura 1985).
Introduced raccoons are suspected to compete severely with,
and possibly exclude, native medium-sized carnivores such as
raccoon dogs (Nyctereutes procyonoides) because they have
similar ecological traits (Ikeda 2000; Komiya 2002). Both
raccoons and raccoon dogs are opportunistic omnivores and
adapt well to various environments. They both consume fruits,
seeds, terrestrial insects, and small mammals for food (Aburaya
1999; Furukawa 2001; Hirasawa et al. 2006; Sasaki and
Kawabata 1994; Stuewer 1943), and use similar resting sites
(Gehrt and Fritzell 1999; Ward and Wurster-Hill 1989).
However, the nature of their interactions is unknown because
only a few studies have investigated the ecology of raccoons
and raccoon dogs living in the same habitat (for raccoon—
Aburaya 1999; Agetsuma-Yanagihara 2001; Suzuki 2003; for
raccoon dog—Furukawa 2001).
A comparison of habitat use by sympatric species allows an
assessment of their interactions because animals generally
select habitats that satisfy their demand for energy, water, and
resting sites to optimize their survival and reproduction (e.g.,
Boyce and McDonald 1999; Chamberlain et al. 2002; Rosenzweig 1991). Therefore, many studies of habitat use have
been conducted to investigate competition between alien and
August 2007
OKABE AND AGETSUMA—RACCOON AND RACCOON DOG HABITAT USE
1091
forest and discuss their relationships in terms of spatial and
temporal habitat use.
MATERIALS AND METHODS
FIG. 1.—Tomakomai Experimental Forest (TOEF) of Hokkaido
University on Hokkaido Island, northern Japan, classified into 7 forest
types according to TOEF Management Maps and Eastern Iburi District
National Forest Management Maps. I: Single-layered deciduous forest
was recently felled, with a canopy , 10 m in height. II: Single-layered
deciduous forest with a canopy . 10 m in height. III: Multilayered
sparse forest that had grown from single-layered forest within 10
years. IV: Multilayered dense forest that had grown from multilayered
sparse forest within 10 years. V: Multilayered dense forest that had
been maintained for at least 10 years. P: Conifer plantation. O: Open
space, including grasslands, swamp, buildings, and roads. Three rivers
passed through or near the study area. Forty study points were
established at approximately 800-m intervals in an 8 5-row grid in
the study area, and a 20 20-m plot was established at the center of
each study point.
native species (e.g., Bryce et al. 2002; Hemami et al. 2004;
Lehtonen et al. 2001; Losos et al. 1993; Wootton 1987). Some
studies of medium-sized carnivores have examined their habitat use based on environmental factors such as forest types
and key resources (Fedriani et al. 1999; Jácomo et al. 2004;
Kaneko 2002; Suzuki 2003). However, the environment can
be assessed at various spatial scales to consider habitat use
(Henner et al. 2004; Johnson 1980; Kotliar and Wiens 1990;
Pedlar et al. 1997). For examining the relationship between
sympatric species, we need to evaluate the environment at
different spatial scales.
In this study, we investigated habitat use by raccoons and
raccoon dogs at 2 spatial scales. Raccoons and raccoon dogs
feed on terrestrial coleopterans (beetles), terrestrial small mammals, aquatic animals, and, especially in autumn, fruits and
seeds (Aburaya 1999; Furukawa 2001; Gehrt and Fritzell 1998;
Hirasawa et al. 2006; Ikeda et al. 1979; Johnson 1970; Sasaki
and Kawabata 1994; Stuewer 1943). Both species use dens in
trees, hollow logs, and thick brush for diurnal resting and for
rearing young (Gehrt and Fritzell 1999; Ward and Wurster-Hill
1989). Therefore, food resources, water availability, and vegetation and forest structure may be important factors determining habitat use. We evaluated factors that may affect habitat
use by raccoons and raccoon dogs in a northern deciduous
Study area and subjects.— The study was conducted primarily in the Tomakomai Experimental Forest (TOEF, approximately 27 km2) of the Field Science Center for the Northern
Biosphere, Hokkaido University (428409N, 1418369E) on
Hokkaido Island, northern Japan. The National Forest of the
Forestry Agency and private forests were adjacent to the
TOEF. Mean annual temperature and precipitation in this area
are 6.48C and 1,200 mm, respectively. One-quarter of the
TOEF consisted of conifer plantations, whereas the remainder
was composed of secondary and natural deciduous forests. The
dominant deciduous species were Quercus mongolica, Kalopanax pictus, Acer, and Alnus. The major planted conifers were
Larix leptolepis, Abies sachalinensis, and Picea glehnii. The
understory was composed of various herbaceous plants, several
species of fern, and 3 species of dwarf bamboo. Three rivers
passed through or near the study area (Fig. 1).
On Hokkaido Island (78,422 km2), captive raccoons were
released or escaped, resulting in the establishment of wild
populations by about 1979 (Ikeda 1999). Raccoons have been
found in the TOEF since the mid-1990s (K. Ishigaki, pers.
comm.). Raccoon dogs are native to Hokkaido Island, and
although they were rarely observed in the TOEF before about
1980, they have since become common in this area (K.
Ishigaki, pers. comm.). Both species are similar in body size,
although raccoons in the TOEF are slightly heavier than
raccoon dogs (mean adult body weight: male raccoon, 5.2 kg [n
¼ 9]; female raccoon, 5.0 kg [n ¼ 15]; male raccoon dog, 4.2
kg [n ¼ 6]; female raccoon dog, 3.8 kg [n ¼ 10]—Ohnishi
2003; Okabe 2004). Other medium-sized carnivores found in
the study area include red fox (Vulpes vulpes schrencki),
Japanese marten (Martes melampus), and American mink
(Neovison vison). Marten were introduced from Honshu Island,
Japan, and mink were introduced from North America. The
TOEF is a designated Wildlife Protection Area, and hunting
has been prohibited since 1968. This study was carried out
following guidelines of the American Society of Mammalogists
(Animal Care and Use Committee 1998).
Habitat use.— Raccoons and raccoon dogs are likely inactive
for extended periods during winter in the TOEF, where the
temperature in midwinter drops to 208C (Kauhala and Saeki
2004; Mech and Turkowski 1966; Whitney 1931). Thus, our
study period was from early summer to autumn (June–
November 2003), when the activity of both species should be
high. We established 40 study points at approximately 800-m
intervals in an 8 5-row grid in the TOEF (Fig. 1). This
interval was shorter than mean maximum home-range width of
individual raccoons and raccoon dogs in the study area (mean
maximum range width: raccoon, 3,415 m [n ¼ 10]; raccoon
dog, 1,103 m [n ¼ 11]—Ohnishi 2003; Okabe 2004); the
individual ranges of each species may be spatially separate or
may overlap one another (Ohnishi 2003; Okabe 2004). Habitat
use by each species was monitored using automatic infrared
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JOURNAL OF MAMMALOGY
cameras with a flash, triggered by animal movement.
Automatic cameras have been used to survey the activity
and behavior of various carnivores such as tigers (Panthera
tigris—Karanth and Nichols 1998), Japanese marten
(M. melampus—Kerry 1998), and American black bears
(Ursus americanus—Martorello et al. 2001). One camera
(Umezawa Musen Denki Co. Ltd., Sapporo, Japan) was placed
at each study point, approximately 1.2 m above the ground
with a downward angle of 308 from vertical. The direction of
each camera was arbitrarily altered at 3- to 5-day intervals.
Each camera could photograph animals entering an approximately 5-m2 area. If necessary, in areas with dense understory,
we reduced the understory within the detection areas to prevent
interference with the infrared sensors. The date and time were
superimposed in a corner of each photograph. To prevent
repetitive photographing of the same animal during 1 visit,
cameras did not function for 2 min after each response of the
sensors.
Photographed animals were identified to species. We then
counted the number of photographs of both species. When
more than 1 animal was found in the same photograph, we used
the number of animals in the photograph. Because some
cameras did not operate for the full duration of the study
because of malfunctions, we determined the number of days
that each camera functioned. We calculated photograph rates
by dividing the number of photographs of each species by the
number of days the camera operated at each study point.
Microhabitat environmental factors.— A 20 20-m plot
was established at the center of each study point. The vegetation within each plot was surveyed during September–
October 2003. In the forest understory, we recorded the percent
cover of herbaceous plants, ferns (mainly Dryopteris crassirhizoma and Osmunda cinnamomea), dwarf bamboos, and bare
ground. Shrub density (i.e., visibility in the range of 1.5-m
height above ground) was classified into 3 levels: low,
intermediate, and high. For trees (i.e., .10 cm in diameter at
breast height [dbh]), we recorded the species and dbh. Total
basal area (m2) of trees was calculated based on the dbh. The
number of deciduous broad-leaved and coniferous trees and the
number of large (dbh . 32 cm) trees that might provide den
sites also were counted. The presence of the vines Actinidia
arguta and Vitis coignetiae, whose fruits are commonly
consumed by raccoons (Aburaya 1999) and raccoon dogs
(Furukawa 2001) in autumn, also was recorded.
Previous studies showed that beetles are one of the main
foods for raccoons and raccoon dogs in summer on Hokkaido
Island (Aburaya 1999; Furukawa 2001). Therefore, abundance
of beetles was investigated using polyethylene pitfall traps
(8.5 cm in diameter, 12 cm deep) containing 50% ethyl alcohol
during 31 July–5 August and 2–5 September 2003. At each
plot, 2 traps were installed 5 m apart for 5 nights in August, and
5 traps were installed at 1-m intervals in a cross shape (Toda
and Kitching 2002) for 3 nights in September. At 2 plots, all 5
traps were damaged in September, probably by carnivores.
Only terrestrial coleopterans were used in the food analysis;
other invertebrates were ignored. The trapped coleopterans
were dried for 3 days at 608C, classified to family, and the
Vol. 88, No. 4
number of individuals was counted and their dry weight was
measured. The abundance of beetles in each plot was defined as
the dry weight (mg) per trap-night in each season.
Macrohabitat environmental factors.— The habitat use of animals will be affected by the surrounding conditions (macrohabitat) such as forest types and key resources (Fedriani et al.
1999; Jácomo et al. 2004; Suzuki 2003), as well as the site
conditions (microhabitat). Therefore, we measured the distance
(m) from each point to the nearest permanent water source (i.e.,
river). In addition, the study area was classified into 7 forest
types according to TOEF Management Maps from 1981, 1991,
and 1994, and Eastern Iburi District National Forest Management Maps from 2001. Type I was single-layered deciduous
forest, recently felled, with a canopy , 10 m in height. Type II
was single-layered deciduous forest with a canopy . 10 m in
height. Type III was multilayered sparse forest that had grown
from single-layered forest within 10 years. Type IV was
multilayered dense forest that had grown from multilayered
sparse forest within 10 years. Type V was multilayered dense
forest that had been maintained for at least 10 years. Type P
was conifer plantation, and type O was open space, including
grasslands, swamp, buildings, and roads. Each forest type
contained 6–13 study points, except for types III and O (type I,
n ¼ 6; type II, n ¼ 7; type III, n ¼ 0; type IV, n ¼ 6; type V,
n ¼ 13; type P, n ¼ 8; type O, n ¼ 0). To determine the
surrounding environments, we calculated the percentage of
each forest type within a 400-m radius of each study point. In
addition, the number of forest patches within this area was
counted as an index of forest fragmentation around each point.
These measurements were obtained using a geographic information system (ArcGIS version 8.3; ESRI Inc., Redlands,
California). Macrohabitat factors dealt with in this study still
corresponded to ‘‘local-level’’ condition rather than ‘‘landscape-level’’ (Henner et al. 2004; Pedlar et al. 1997).
Data analysis.— We evaluated the habitat use of both species based on photograph rates. We assumed that places
with high photograph rates included some important environmental factors for the species even if we could not individually identify photographed animals. We did not evaluate the
relative densities of each species because differences may
have existed between the species in their responses to the
camera.
To examine environmental factors (Table 1) that can affect
habitat use by both species, we used generalized linear models
(McCullagh and Nelder 1989). We assumed a negative binomial error structure and used a log link function. The response
variables were divided by the number of camera-days at each
point in order to consider differences in photographing effort
between study points. We evaluated full models containing all
environmental factors measured in the microhabitat and
macrohabitat of both species respectively (Table 1), and then
carried out backward stepwise multiple regression, deleting the
factor with the lowest level of statistical significance at each
step. Subsequently, we selected the model that had the lowest
Akaike information criterion score (Table 2). The statistical
significance of each environmental factor in the best models
was examined using the likelihood ratio test.
August 2007
OKABE AND AGETSUMA—RACCOON AND RACCOON DOG HABITAT USE
TABLE 1.—Environmental factors at the microhabitat scale and
macrohabitat scale. Microhabitat environmental factors were recorded
in a 20 20-m plot at the center of each study point. Macrohabitat
environmental factors were measured within a 400-m radius of each
study point using a geographic information system. In addition, the
distance to the nearest permanent water source (i.e., river) from each
study point was measured.
Spatial scale
Microhabitat
Macrohabitat
Environmental factor
a
Understory cover
Shrub density (low, intermediate, high)
Vines (present, absent)b
Number of trees
Number of deciduous trees
Number of coniferous trees
Number of large trees
Basal area (m2)
Number of tree species
Beetle abundance (mg day1 trap1 in August, September)c
Forest within 400 md
Number of forest patches within 400 m
Distance to water source (m)
a
Percent cover by ferns, dwarf bamboos, other herbaceous plants, or bare ground.
Actinidia arguta and Vitis coignetiae.
c
n ¼ 38.
d
Percent type I, type II, type III, type IV, type V, type P, and type O.
b
RESULTS
Photograph rates.— Cameras operated from 144 to 183 days
¼ 166.7 days), for a total of 226,720 camera-days. We
each (X
obtained 90 and 313 photographs of raccoons and raccoon
dogs, respectively. The photograph rate of raccoon dogs (0.046
photos per day per study point) was significantly higher than
that of raccoons (0.013 photos per day per study point;
Wilcoxon’s signed-ranks test, Z ¼ 3.054, n ¼ 40, P ¼ 0.001).
However, the number of study points at which animals were
photographed did not differ significantly between the species
(raccoon: 29 points; raccoon dog: 35 points; chi-square test,
v2 ¼ 1.953, d.f. ¼ 1, P ¼ 0.162). The number of study points
at which only raccoons appeared was 2, that at which only
raccoon dogs appeared was 8, and that where both species
appeared was 27. At these 27 study points, a raccoon and
a raccoon dog were photographed consecutively within a 24-h
period in 11 cases. No significant correlation was observed
between the photograph rates of the 2 species at each point
(Spearman’s coefficient of rank correlation, q ¼ 0.233, n ¼ 40,
P ¼ 0.145).
Most photographs of raccoons were taken at night (1800–
0600 h; 94.4%), whereas photographs of raccoon dogs were
taken both during the day (0600–1800 h; 26.5%) and at night
(73.5%). Raccoon dogs were more frequently photographed
in the daytime than raccoons (chi-square test, v2 ¼ 16.788,
d.f. ¼ 1, P , 0.001).
Habitat use and microhabitat factors.— By generalized
linear models analysis, 6 microhabitat factors were included
in the best models for both raccoons and raccoon dogs (Table
2). Photograph rates of both species were positively associated
with fern cover in the understory (raccoon, P ¼ 0.024; raccoon
1093
dog, P ¼ 0.00004). Number of trees and total basal area in each
plot were also included in the models of both species although
these factors individually did not have significant effects.
However, raccoons and raccoon dogs showed different associations with other environmental factors. Photograph rate of
raccoons was negatively related to the cover of dwarf bamboos
(P ¼ 0.00024) and that of other plants (P ¼ 0.00041), and also
negatively related to the number of coniferous trees (P ¼
0.001). On the other hand, photograph rate of raccoon dogs was
negatively related to shrub density (P ¼ 0.001), but positively
related to the presence of the vines A. arguta or V. coignetiae
(P ¼ 0.019). Abundance of beetles was not included in the best
model for either species.
Habitat use and macrohabitat factors.— Only 2 macrohabitat factors were included in the best models for raccoons
but 5 microhabitat factors were included in the best models for
raccoon dogs (Table 2). Raccoons and raccoon dogs showed
very different habitat use in response to macrohabitat factors.
Type IV forest was negatively related to habitat use by raccoons (P ¼ 0.002). In contrast, type V and type P forest were
positively related to, and the number of forest patches within
400 m of the study points was negatively related to, habitat
use by raccoon dogs (type V, P ¼ 0.002; type P, P ¼ 0.031;
forest patches, P ¼ 0.0004). Distance to the nearest permanent
water source was not included in the best model for either
species.
DISCUSSION
In Japan, there are concerns that introduced raccoons will
exclude native raccoon dogs as a result of direct and indirect
competition (Ikeda 2000; Komiya 2002). However, little information has been collected regarding their ecology and potential
interspecific competition. The intensity of competition between
sympatric species should be assessed from various aspects of
their ecology such as diet, seasonal and diurnal activity patterns, demography, and social system. Moreover, habitat use
and environmental requirements should be examined at various
spatial scales (Fischer and Gates 2005; Hemami et al. 2004).
Thus, we investigated the habitat use of introduced raccoons and native raccoon dogs at 2 spatial scales in the same
study area.
Both species were positively associated with fern coverage
in the understory (Table 2). Hirasawa et al. (2006) reported
that raccoon dogs feed on ferns to some extent from spring to
summer. In addition, ferns tend to grow in humid places where
amphibians and other invertebrates may be abundant. However, most other environmental factors had different effects on
the habitat use of these species, irrespective of spatial scale
(Table 2). Habitat use of raccoons was affected by more factors
at the microhabitat scale than at the macrohabitat scale, in
contrast to raccoon dogs. These results suggested that the 2
species show different responses to environmental factors at
both macro- and microscales. Movement patterns of individual
animals within their home ranges also differ between these
species; Ohnishi (2003) and Okabe (2004) reported that
raccoons tend to have broader ranges with multiple core areas,
Type III
Type IV
Forest within 400 m
Null
1
1
1
1
1
Number of trees
Number of coniferous trees
Basal area
Macrohabitat
1
1
1
d.f.
Ferns
Dwarf bamboos
Other herbaceous plants
Understory cover
Microhabitat
Null
Environmental
factor
0.087
10.067
0.404
10.735
3.061
5.082
13.470
12.506
Deviance
38
37
39
35
34
33
38
37
36
39
Residual
d.f.
Raccoon
52.799
42.732
52.886
51.769
41.034
37.974
78.149
64.679
52.173
83.231
Residual
Deviance
0.768
0.002
0.525
0.001
0.080
0.024
,0.001
,0.001
P (v2)
þ
þþ
Number of forest patches
within 400 m
Type III
Type V
Type P
Forest within 400 m
Null
Macrohabitat
Number of large trees
Shrub density
Vines
Ferns
Number of trees
Basal area
Understory cover
Microhabitat
Null
Environmental
factor
1
1
1
1
1
2
1
1
1
1
d.f.
12.346
0.001
9.594
4.646
3.076
13.690
5.464
16.779
0.673
1.458
Deviance
35
38
37
36
39
35
33
32
38
37
36
39
Residual
d.f.
Raccoon dog
44.318
70.904
61.311
56.665
70.905
63.191
49.501
44.037
68.398
67.725
66.267
85.197
Residual
Deviance
þ
þ
,0.001
þ
þþ
0.987
0.002
0.031
0.077
0.001
0.019
,0.001
0.411
0.221
P (v2)
TABLE 2.—Environmental factors included in the best models to explain habitat use (measured as photograph rate, see ‘‘Materials and Methods’’) by raccoons and raccoon dogs. Significant
environmental factors irrespective of spatial scales were different between raccoons and raccoon dogs except for fern coverage. The significance of each explanatory variable was tested by
likelihood ratio tests. þ refers to positive effect on habitat use (þþ, P , 0.01; þ, P , 0.05) and refers to negative effect on habitat use (, P , 0.01; , P , 0.05).
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August 2007
OKABE AND AGETSUMA—RACCOON AND RACCOON DOG HABITAT USE
whereas raccoon dogs tend to have narrower ranges with a
single core area in the TOEF.
Temporal segregation of habitat use has been suggested as
a mechanism that reduces competition between species (e.g.,
Fedriani et al. 1999; Lack 1971; Schoener 1974; Serafini and
Lovari 1993). For example, native raccoons and Virginia
opossums (Didelphis virginiana) in North America have highly
overlapping habitats and food resources (Kissell and Kennedy
1992; Lotze and Anderson 1979; McManus 1974). However,
they may use the same habitats at different periods during the
night (Ladine 1997), resulting in temporal niche partitioning. In
our study area, activity of raccoons was concentrated at night,
whereas one-fourth of the activity of raccoon dogs was
recorded during the daytime. Diurnal activity in raccoon dogs
also has been observed in other areas of Japan that lack
raccoons (Iwamoto et al. 2002; Ward and Wurster-Hill 1989).
Therefore, the diurnal activity of raccoon dogs was not likely
caused by competition with raccoons, but may help limit it.
The population density of raccoons (1.1–2.9 individuals/km2)
was similar to that of raccoon dogs (2.1–2.6 individuals/km2)
in the study area (Ohnishi 2003). However, if local competition
and exclusion were occurring, a significant negative correlation
would be expected between the abundance of each species
(e.g., Hallett et al. 1983; Hansson 1983). We found no such
negative correlation between the photograph rates of raccoons
and raccoon dogs at each study point. Observations at a garbage
dump on Honshu Island, Japan, suggest that alien raccoons
and native raccoon dogs meet infrequently, and even when
agonistic interactions occur, the dominance order is not fixed in
these species (Agetsuma-Yanagihara 2004). Therefore, direct
competition (contest) between these species for food may not
be severe. Both raccoons and raccoon dogs are opportunistic
omnivores, possibly facilitating their coexistence. Thus, competition between raccoons and raccoon dogs is currently likely
to be limited in the study area. The different responses of
the species to environmental factors suggest that the abundances of these species can be changed by habitat alterations.
Therefore, habitat management might be important to conserve native raccoon dogs and control alien raccoons. Further
research is needed to determine how and what magnitudes of
habitat alteration will change their populations.
ACKNOWLEDGMENTS
We thank Profs. T. Hiura and M. Murakami, Drs. D. Fukui, G.
Takimoto, E. Nabashima, K. Tanaka, and U. Nishikawa, and Mr. T.
Hino of Hokkaido University; Dr. R. Powell, and 3 anonymous
referees for many helpful comments on the manuscript. We also thank
Dr. H. Hirakawa of the Forestry and Forest Products Research Institute
for teaching us how to use the automatic cameras, Mr. K. Itagaki for
analysis of aerial photographs, Mr. T. Hirao for statistical analysis, Mr.
K. Ohnishi and Ms. R. Tsuji of Hokkaido University, and all staff and
students at the TOEF for assistance during the fieldwork. This study
was supported financially by Experimental Research of the Forest
Research Station, Field Science Center for Northern Biosphere, of
Hokkaido University and a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, and Culture of Japan (15207008,
1620801400, and 18380086).
1095
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ecology of raccoon (Procyon lotor) in Aichi Prefecture. Special
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Submitted 11 April 2006. Accepted 5 December 2006.
Associate Editor was Roger A. Powell.