125

Present Status of Invasive Alien Raccoon and its Impact in Japan
Tohru IKEDA1, Makoto ASANO2, Yohei MATOBA3 and Go ABE1
1

Graduate School of Letters, Hokkaido University,
Kita 10 Nishi 7 Kita-ku, Sapporo, Hokkaido 060-0810, Japane-mail: tikeda@reg.let.hokudai.ac.jp
2
Faculty of Applied Biological Sciences, Gifu University,
Yanagido 1-1, Gifu, Gifu-ken 501-1193, Japan3
Department of Veterinary Parasitology, Rakuno Gakuen University,
Bunkyoudai, Ebetsu, Hokkaido 069-8501, Japan

Abstract
Irresponsible breeding and release of pet raccoons (Procyon lotor) has caused their naturalizationin Japan. The raccoons have already naturalized in 42 of Japan’s 47 prefectures, and there has been a remarkable increase in agricultural (cattle breeding) and urban areas, where the raccoons can find foodand hide easily. Their home range size varies widely according to the habitat, ranging from 35 ha inurban areas to 2,219 ha in forests (mean : 299.1 ha). The raccoon avoids energy loss in winter bysemi-hibernation. It has opportunistic and omnivorous feeding habits, taking crops and fruit in agricultural areas and native species in forests. It also preys on indigenous species such as the Japanese crayfish (Cambaroides japonicus) and Ezo salamander (Hynobius retardatus). Reproductive observations
have shown high productivity (reproductive rate : 66% in yearlings and 96% in adults, litter size : 3.6 inyearlings and 3.9 in adults) and a potentially rapid rate of population growth (0.20 to 0.25). Intensive
eradication guided by biological data will be indispensable to controlling invasive alien raccoons.
Key words: impact, invasive alien raccoon, management, naturalization

1. Introduction
After the ratification of the ‘Convention on Biological Diversity,’ invasive alien species issues became a major concern in Japan. Invasive alien species
are considered to be the one of the most importantcauses of extinction and decline of wild native species(Margin et al., 1994; Williamson, 1999). In particular,invasive alien mammals are thought to have serious
impacts on native ecosystems because of their hightrophic level.
With Japan’s spectacular economic growth, numerous species of mammals have been imported into
Japan as pets. The number of alien mammals is on theincrease with the increase of imported mammals, andover 30 species of mammals have thus far naturalizedin Japan (The Committee on Mammal Conservationand Management, 1999).
Among these alien mammals of Japan, the raccoon(Procyon lotor) is a representative nuisance. The raccoon is very popular not only for its cute appearance
but also its comical behaviors (Zeveloff, 2002). Its
round, funny face with a bandit’s mask across the eyes
and a striped bushy tail create a humorous impression,and people find its habit of washing of food prior to
Global Environmental Research8(2)/2004: 125-131
printed in Japaneating curious. It prefers waterfronts generally, but iswell known to be highly adaptive to various environments owing to its omnivorous feeding habits(Sanderson, 1987).
This species came from North America. In addition
to being introduced to Japan, it was introduced into
the Caribbean islands in 1932 (Sherman, 1953),
Germany in 1934 (Lever, 1985) and the Soviet Union
in 1936 (Aliev & Sanderson, 1966), where it caused
heavy damage to crops or native ecosystems.
In Japan, after the smash hit of the animated cartoon ‘Rascal Raccoon’ on TV in 1977, the raccoon
became popular as pet animal and many raccoons
were imported (Ikeda, 1999a). The raccoon, however,is fierce in nature, and comes to show its wildness as
it grows up. It is thought that many raccoon breeders
had troubles with their raccoons and abandoned them.
The raccoon is also clever with its hands, and can escape from simple breeding cages easily. As a consequence of irresponsible abandonment and escapesfrom captivity, many raccoons have naturalized invarious regions in Japan (Fig.1). Including temporalcases, the raccoon has already naturalized in 42 ofJapan’s 47 prefectures. The raccoon has so wide afood repertory that many native species are exposed to©2004 AIRIES126

T. IKEDA et al.

the menace of raccoon predation.
This paper is a review of the spread of the invasive
alien raccoon and its impact in Japan. We also attempt
to compare its population trend data with those of the
raccoon dog (Nyctereutes procyonoides) to point out
the former’s impact on native species specifically, andwe attempt to develop effective countermeasures for
its control.

Hokkaido Prefecture, in 1979 (Ikeda, 1999a) (Fig.1).
About ten raccoons escaped from a breeding cage andnaturalized in a livestock farming area. Owing to multiple escapes and abandonment, the raccoon has
spread throughout the west-central and eastern part of
Hokkaido at present (Fig.2).
In Hokkaido, the raccoon naturalized in the livestock farming area initially (Fig.3). Figure 4 shows

2. History and Process of Naturalization of
the Invasive Alien Raccoon in Japan.
The first naturalization of raccoons in Japan occurred in Inuyama City, Aichi Prefecture, in 1962
(Ando & Kajiura, 1985) (Fig.1). Some raccoons escaped from a zoo, then colonized Gifu Prefecture. In
addition, a raccoon breeder abandoned over 40 raccoons in Kani City, Gifu Prefecture in 1982. Most ofthese raccoons were captured, but the remaining raccoons still continue to harm crops.
The next naturalization occurred in Eniwa City,

Fig. 2 Distribution of invasive alien raccoons in Hokkaido
Prefecture.
Source: Natural Environment Division, Office of Environmental Affairs, Department of Environment andLifestyle, Hokkaido Prefectural Government.

Fig. 1 Distribution of naturalized raccoons in Japan.
: Initial naturalized area
1 in Inuyama City in 1962
2 in Eniwa City in 1979
3 in Kamakura City in 1988

Fig. 3 Raccoon family roaming in a cowshed.
(Photograph by the Raccoon Research Group)

Fig. 4 Damage to livestock farms by invasive alien raccoons in Eniwa City in
1996.

Present Status of Invasive Alien Raccoon and its Impact in Japan127

damage to the livestock farms by raccoons. It is clearthat the raccoons prefer cattle breeding farms and fish
breeding farms to other livestock farms. At cattle
breeding farms, the raccoons are likely to get plenty ofcorn, the raccoon’s greatly preferred food, from thecompound cattle feed throughout the year, and canfind safe cover, such as lumps of dried pasture grass,
for reproduction. As Giles (1940) and Tester (1953)highlighted the importance of corn in the diet of the
raccoon, the raccoons roaming around the cattle
breeding farm in Eniwa City also showed a high dependence on corn from the compound feed even after
the harvest of corn in the field. In November, 80% of
raccoon feces contained undigested corn (Yoshino,1994). A fish breeding farm also made fish available
for food, but was not suitable for reproduction. As aconsequence, it seemed that the raccoons reproduced
at the cattle breeding farm, then expanded their distribution mainly along the river.
The third naturalization occurred in Kamakura City,in 1988 (Fig.1). The process of naturalization in
Kamakura City was different from that in Hokkaido.
The main cause of the naturalization was an escapefrom captivity, as with the other places, but the raccoon established its habitat in an urban area. There aremany old wooden houses, Buddhist temples andShinto shrines in Kamakura City, and these Japanese-style architectures have some air vents under theeaves and the floors. The raccoon invaded via these air
vents and built nests under the roofs (Fig.5). In urban
areas, the raccoon can access garbage easily, and catch
carp and goldfish from ponds in gardens. The raccoon
can also use drainpipes as safe travel paths that wereused by the raccoon dog before the raccoon invasion.
Urban areas are also available for the raccoon, so it isexpanding its distribution. Figure 6 shows information
on invasions by raccoons in Kamakura City in 2001.
The raccoons have spread out all over the city at thismoment.
In other areas where the raccoon has invaded, themain causes seem to be escapes and abandonment.
From an ecological point of view, the raccoon cannaturalize in all environments in Japan, but we must

Table 1 shows the home range size of the invasive
alien raccoon in Japan determined by radio telemetry
method. The home range size varies widely according
to its habitat. The largest home range size was 2,219 ha
in forested area, and the smallest was 35 ha in an urban area. The range size in urban areas (mean: 49.0 ha)
was smaller than those in suburban and rural areas(mean : 358.0 ha) (p < 0.01, Mann-Whitney’s U-test).
In forested areas of Hokkaido, the home range sizeof the invasive alien raccoon tended to diminish remarkably as the temperature dropped (Ikeda, 1993).
The raccoon used only river sides for its paths in thesnowfall season. It seemed that the raccoon had trouble walking in deep snow coverage according to ourobservations. In midwinter, the raccoon avoids energy
loss by remaining motionless in the hollow of a tree orin a vacant house.
The raccoon is thought to have a polygamous orpromiscuous mating system (Zeveloff, 2002). The
invasive alien raccoon in Japan also showed a polygamous mating system. The male raccoon tended tokeep more than one female in its home range. The
raccoon in Hokkaido mated from January throughMarch, with a peak in February. In this breeding
period, the male raccoon tended to come and go
among a few females in its home range, while thefemale raccoons kept still in their dens.
These activities of the invasive alien raccoon in
Japan are almost the same as its activities in its placeof origin (Zeveloff, 2002). It seems that the invasive

Fig. 5 Raccoon invading a house.
(Photograph by the Raccoon Research Group)

Fig. 6 Entry into houses or courtyards by invasive alien
raccoons in Kamakura City in 2001.

pay special attention to agricultural and urban areas toprevent more multiplication of the raccoon.

3. Behavior of the Invasive Alien Raccoon in
Japan.

Source: Kamakura City

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T. IKEDA et al.

alien raccoon can establish its niche in Japan easily.
Furthermore, it has no natural enemies in Japan suchas the bobcat (Felis rufus) or the coyote (Canis
latrans). There is a danger that the invasive alien raccoon will continue to increase its numbers throughout
the nation.

4. Reproductive Characteristics of the Invasive Alien Raccoon
Table 2 shows the pregnancy rate and mean litter
size of invasive alien raccoons in west-central
Hokkaido by analysis of placental scars or fetuses in
the uterus (Asano et al., 2003). Juveniles (that year’s
litters) were distinguished from yearlings and adults(over 2 years of age) by examining tooth eruption androot foramina closure of the canines. The invasive
alien raccoon showed very high productivity. The
Table 1mean pregnancy rate was 66% in yearlings and 96%
in Adults. Litter sizes ranged from 1 to 7 and averaged
3.6 in yearlings and 3.9 in Adults. These reproductive
characteristics are almost the same or slightly higher
than those reported in North America (Ritke, 1990;
Stuewer, 1943; Fritzell et al., 1985). The rate of population growth in west-central Hokkaido was estimatedto range from 0.20 to 0.25 without harvest mortality(Asano et al., 2003). Based on these data, it is clearthat without relevant measures to control the raccoon,
it is capable of population expansion.

5. Feeding Habits of the Invasive Alien Raccoon
The invasive alien raccoon shows opportunistic
and omnivorous feeding habits in response to its habitat environment. In general, the raccoon takes animal

Home range size of invasive alien raccoons in Japan determined by radio telemetry
methodEach home range size shown is the maximum size in each period. We attached collar transmitters(Type 8C by ATS Inc., weight:120 g) to raccoons, and plotted locations by triangulation methodwith a 3-element Yagi antenna (YA-23L) and mobile receiver (Yaesu FT290mkII).

Home range
size (ha)
2219
509
417
152
184
144

Sex

PeriodStudy area

Male
Male
Male
Male
Male
Male

Jun.1992-Jan.1993
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Mar.2000-May 2000

Eniwa
Eniwa
Eniwa
Eniwa
Eniwa
Nopporo77

Male

Apr.2000-May 2000

Nopporo

40
47
648
313
310
278
207
195
138

Male
Male
FemaleFemaleFemaleFemaleFemaleFemaleFemaleSep.2000-Oct.2000
Sep.2000-Oct.2000
Sep.1993-Oct.1994
Jun.1992-Jan.1993
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Sep.1993-Oct.1994
Nov.1999-May 2000

Kamakura
Kamakura
Eniwa
Eniwa
Eniwa
Eniwa
Eniwa
Eniwa
Nopporo114

Female Nov.1999-May 2000 Nopporo

100
81
74
35

FemaleFemaleFemaleFemaleSep.1993-Oct.1994
Sep.1993-Oct.1994
Sep.2000-Oct.2000
Sep.2000-Oct.2000

Eniwa
Eniwa
Kamakura
Kamakura

Habitat type
ForestForestForestSuburban
Suburban
Forest park surrounded byresidences
Forest park surrounded byresidences
Urban
Urban
ForestForestForestForestForestForestForest park surrounded byresidences
Forest park surrounded byresidences
Suburban
Suburban
Urban
Urban

Table 2 Age-related pregnancy rate and mean litter size of invasive alien
raccoons collected in west-central Hokkaido in 1999-2000.
(Asano et al., 2003)
Age(years)

N

0
1
2
3
4
≧5
Total

69
71
43
27
18
14
242

Pregnancies
N
%
0
0
47
66
41
95
25
93
18
100
14
100
145
84

Mean litter size (±SD)
3.6±1.3
3.7±1.2
4.1±1.2
3.7±1.5
3.8±1.3
3.8±1.3

Present Status of Invasive Alien Raccoon and its Impact in Japanfat in summer and vegetable fat in autumn in preparation for semi-hibernation in winter.
In agricultural areas of Hokkaido, the raccoon
damages crops and fruits such as corn, melons, watermelons, strawberries, paddy rice, soybeans, potatoes,
beets, oats, and so on in summer and autumn. It eats
livestock feed, feed grain and pasture grasses, too. The
total amount of agricultural damage amounts to
30,000,000 yen every year. The raccoon eats crops
and fruit only in the harvest season, excluding driedcorn in compound cattle feed which is available
throughout the year. The raccoon takes beetles andhornets (Vespula flaviceps) in summer and autumn(Murayama, 1991; Yoshino, 1994; Nakamura, 1994).
Research in Nopporo Forest Park surrounded by agricultural and residential areas in Hokkaido showed thatbower actinidia (Actinidia arguta) and arthropods occurred in 90% of raccoon scats in autumn (Yutani,1999).
In forests, the raccoon preyed on various native
species. So far we have recorded their predation on
small mammals such as the gray red-backed vole
(Clethrionomys rufocanus bedfordiae), snakes, frogs,
dragonflies, damselflies, bees, butterflies, cicadas,
shrimp, shellfish, wild vines and Japanese yew (Taxus
cuspidata) by dissection of raccoons trapped during a
nuisance control harvest.

129

that the raccoon preys on the Japanese crayfish(Cambaroides japonicus) (Hori & Matoba, 2001), and
it is likely that the raccoon preys on the Ezo salamander (Hynobius retardatus) and some species of frogs

Fig. 7 Main sites of captures of raccoons and raccoon dogs in
Nopporo Forest Park.

6. Impacts of the Invasive Alien Raccoon
Besides damage to crops, the raccoon also poses athreat of spreading infectious diseases. The raccoon
can transmit raccoon roundworm (Baylisascaris procyonis) infection (Miyashita, 1993). Raccoon roundworm has not been detected in naturalized raccoons
yet, but we should be concerned about this infection
because it has been detected in a raccoon in captivity.
Furthermore, raccoons transmit rabies. It is feared thatrabies could spread throughout the nation carried byraccoons if the disease should invade Japan (Ikeda,
1999a).
As for the impacts on native ecosystems, competition with some native species is likely occurring.
Resource competition with the raccoon dog and thered fox (Vulpes vulpes) turned these animals out into
unfavorable habitats (Ikeda, 1999a). In Nopporo
Forest Park, the raccoon occupied the peripheral partsof the park where animals could access crops easily,so the raccoon dog was pushed deeper into the forest(Fig.7). In this area, the number of the raccoon dogs
increased after an active harvest of the raccoon, but
decreased again as the number of raccoons recovered(Fig.8). Another example of a raccoon impact is atake-over of a hollow tree from an owl for a breeding
nest, which disrupted the owl’s reproduction (Fig.9).
In addition to resource competition, direct predation on valuable native species is another serious
problem posed by the invasive alien raccoon. An investigation by digestive tract analysis made it clear

Fig. 8 Fluctuation in number of captured raccoons andestimated population of raccoon dogs in Nopporo
Forest Park.

Fig. 9 Raccoon taking over an owl’s nest for breeding.
(Photograph by T. Ikeda)

130

T. IKEDA et al.

judging from the shape of leftover carcasses (Ikeda,
2002).
Raccoon predation on birds and eggs is common in
North America (Zeveloff, 2002). In Nopporo Forest
Park, some raccoons attacked a reproductive colony ofgrey herons (Ardea cinerea), which subsequently
abandoned their breeding grounds in 1997 (Ikeda,
1999b; Ikeda, 2000).

7. Present Measures against the Invasive
Alien Raccoon in Japan
Nuisance control harvests of the invasive alien raccoon were conducted in various places in Japan, butthey amounted to no more than a bandage measure,because the decrease in damage to crops reduced thevictims’ desire to catch the invasive alien raccoon.
The Hokkaido government made a municipal bylaw to put raccoon breeders under obligation for registration starting 2001 (Ono, 2002). Under this municipal bylaw, raccoon breeders must notify the governorof their possession of raccoons. This measure seemed
to be effective at stop irresponsible releases, preventing new naturalization of the raccoon.
The Hokkaido government formulated basic guidelines for the control of the invasive alien raccoon, andset eradication from the wild as its goal in 2003. The
Hokkaido government also started a scientific action
plan toward eradication of the raccoon. This plan was
intended to eradicate the invasive alien raccoon in thecourse of ten years, but faced difficulty due to lack ofbudget.
Other prefectures continue to conduct nuisancecontrol harvests continually. They are expected toswitch from nuisance control harvesting to scientificcontrol programs based on ecological population data
to eliminate the impacts on native ecosystems.

8. Toward Creation of Effective Management Measures
Due to its excellent adaptability to various environments and its lack of natural enemies in Japan, theinvasive alien raccoon has increased in number andcaused serious damage to native ecosystems and human economy.
The invasive alien raccoon shows high reproductive power and a potentially rapid rate of population
growth, thus we certainly will be unable to control the
raccoon if we resort only to nuisance control harvesting. Unfortunately, public awareness of invasive alien
raccoon issues is low, except in some prefectures
where damage from raccoons is serious. It must be
noted that educational efforts will be needed regarding
invasive alien raccoon issues, especially their irreversible impacts on native ecosystems.
As for methods of control, intensive extermination
under scientific control programs on the basis of adaptive management rather than nuisance control harvests,

will be indispensable to controlling the invasive alien
raccoon. It will be necessary to collect detailed population data and reproductive parameters in cooperation
with prefectural governments. These data should thenbe used to estimate a culling rate that can reduce oreven eradicate the population.
The Invasive Alien Species Act will be enforced in
2005. We hope that scientific raccoon control programs will start in many parts of the country.

Acknowledgements
We would like to acknowledge the contributions of
the Raccoon Research Group menbers, Dr. Norio
Ohtaishi, Dr. Masatsugu Suzuki, Laboratory of Wildlife Biology (Graduate School of Veterinary Medicine,
Hokkaido University) member, Dr. Mitsuhiko
Asakawa, members of the Department of Veterinary
Parasitology (Rakuno Gakuen University) and the
Research Group of Regional Sciences (Graduate
School of Letters, Hokkaido University). Great appreciation is extended to the Natural Environment Division (Department of Environment and Lifestyle,
Hokkaido Prefectural Government) and KamakuraCity. Our study was supported in part by a grant from
the Ministry of the Environment as part of the Global
Environment Research Programme.
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(Received 28 December 2004, Accepted 31 December 2004)