149

Crows Problems in Sapporo Area
Makiko TAKENAKA
Center of Education and Research, Hokkaido Tokai University,
1-1-1 Minamisawa 5-jo, Sapporo, Hokkaido, 005-8601 Japane-mail:sturnuscorvus@jcom.home.ne.jp

Abstract
Crows in urban and residential areas have caused friction and problems in Sapporo, as in otherurban areas in and out of Japan (Ministry of Environment, 2001; Vuorisalo et al., 2003; Gorenzel et al.,2002). The problems include garbage depots messed up by crows, attacks on passers-by particularly
near nests, and damage to fruits and crops. Crows are often regarded as a nuisance and arouse feelingsof fear or resentment often based on false assumptions among some citizens. This results in frequentclaims from the citizens that the city must eradicate as many crows as possible. However, the management and control of crow populations, if necessary, should be based on correct data and observation of
their ecology, behavior, distribution and abundance. These data may also be used to improvise measures to drive crows away effectively from undesirable areas. This paper describes the status of two
common crow species, Corvus corone and C. macrorhyncus, in the Sapporo area in the winter of 2002
and 2003. The results of a roost site survey were compared with some of the results obtained in
between 1991 and 2001, which proved that the crow population stayed fairly constant between those
years. Roadside censuses revealed that the temporal and spatial distributions of these two species
varied considerably from late autumn to winter. Garbage depot surveys illustrated clearly that protecting garbage depots was an effective method for curbing the number of crows in the neighborhood.
Municipal and residents’ efforts are also described, which are aimed at finding better ways of coexistingwith crows rather than haphazardly eliminating them. Though still at an early stage, the city’s projectto understand the ecology of crows as wild bird species is expected to be helpful in terms of both raising
citizens’ awareness of the advantages of peaceful coexistence with crows and devising methods to curb
the numbers in undesirable areas.
Key words: crow problems, garbage depots, urban areas, winter roost surveys

1. Introduction
Sapporo, the capitol of Hokkaido Prefecture andthe largest city in northern Japan, is highly urbanizedwith a population of 1.8 million. The Sapporo area
includes the adjacent parts of Ebetsu, Otaru,
Kitahiroshima, and Eniwa. Like most parts of
Hokkaido, the area is characterized by heavy snowfall
in winter, with an average snow accumulation of 4 to
6 m and a cooler summer.
Of the four species of crows, the carrion crow
(Corvus corone), the jungle crow (C. macrorhyncus),
the rook (C. frugilegus) and the eurasian jackdaw(C.monedula) observed in the Sapporo area, the latter
two are rare, found locally and briefly during winter.
The former two species are the commonest residents
in the area. They are found sympatrically, while theformer tends to inhabit more open and rural areas thanthe latter as reported by Higuchi (1979).
This paper reports on the current status of the two

species of crows, crow-related problems in the area,
and attempts by the municipal government and citizens to try to find better ways to curb the number ofcrows attracted to residential and commercial areas.

2. Jungle Crows and Carrion Crows – Their
Winter Distribution and Abundance
2.1 Communal roost occupation and crow counts
at winter roost sites
Both Jungle and Carrion Crows show a strong
tendency to roost communally from autumn to spring
until the onset of the breeding season. In the
Sapporo area, there are numerous spring and summer/
autumn roosts at which several tens to a few hundred
crows assemble. Crows abandon most of theseroosts by the end of November. They, then, begin tooccupy the winter roost sites which are less numerous
than those occupied in the other seasons (Fig. 1). In
the Sapporo Area, the locations of winter roosts seem

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M. TAKENAKA

to be quite fixed, not changing from year to year, except in 1993/1994 when crows were found to occupy a
new roost site in downtown Sapporo and 2002/2003
when the locations of two of the winter roosts changedslightly.
Winter roosts are relatively fixed in terms of locations and numbers (Takenaka, 1999). Counting crows
at these roost sites should give a fairly accurate assessment of crow populations in the study area. Counting the number of crows at their winter roosts should
give an accurate numbers of crows, if it is assumed
that all of the crow populations in the area assemble atthese sites. The counts must be done simultaneously at

Fig. 1

Distribution of spring-autumn roosts and winter roosts
in the Sapporo area in 2002 and 2003. There are
numerous other spring-autumn roost sites in addition
to those shown.
Table 1all of the roost sites for improved accuracy, as it has
been frequently observed that individuals switch
between roosts.
To assess the population sizes of the crow species
in the Sapporo area, I conducted simultaneous crowcounts at the five winter roost sites in central Sapporo
and one in O-asa from November 2002 to early March
2003. In this survey, the numbers of jungle andcarrion crows were counted separately when possible,or proportions of the two species were determined toestimate the numbers of both species found at eachroost in cases separate direct counts were not possible.
The results of crow counts in 2002/2003 are shownin Fig. 2. For comparison, the crow counts conducted between 1991 and 2001 at four of these winterroost sites are summarized in Table 1. In the interval
between these years, jungle and carrion crows were
not counted separately. The numbers of assembling
crows at Jozankei and O-asa seemed basically unchanged from the 1991-2001 period to 2002/2003.

Fig. 2The number of crows assembling at the six winterroost sites in the Sapporo area in 2002/2003.

Some crow counts at winter roosts in Sapporo between 1991 and 2001. The largest count isindicated for each month. Docho was not occupied prior to 1993 (indicated by grey).

Maruyama

Docho

Moiwakita

MinamisawaKawazoe

Month
Jan
Feb
Nov
Dec
Jan
Feb
Nov
Dec
Jan
Feb
Nov
Dec
Jan
Feb
Nov
Dec

1991

1992
2220

1993 1994

1995

1996

1998 1999

2000

2001

1160
600
3530

1100
110
100
800
3000

2500

3000

300
2450
0

2560
100

1380
1650

400
2215

1360
800

350
0
1250

110
1000
450

300

Crows Problems in Sapporo Area

Prior to 2002, 100 to 500 individuals were observed toroost at Jozankei (Takenaka, unpublished) and 1,000
to 2,000 at O-asa (Nirasawa & others, pers. comm.).
Based on these data and information, it is assumed
that there has been little change in the number ofcrows assembling in the Sapporo area.
The total number of assembling crows increased in
November, reaching a plateau in December throughMarch (Fig. 2). Although the number of crows remained almost the same, the numbers of individuals
roosting at each site changed considerably. For
example, on December 28, 2002, 3,230 crows assembled at Maruyama roost but the number decreased to1,585 on January 11, 2003. On the other hand,approximately 2,890 individuals assembled at Docho
on December 28, 2002, but 4,470 on January 11, 2003.
On January 11, 1,000 to 1,500 crows, which had cometo the pre-roosts at Maruyama, were observed taking
off and heading toward Docho. Snow removal
operations in Maruyama with large rotary snow
removal vehicles and many dump trucks, which usually last till midnight, probably caused some crows to
temporarily abandon the roost. Contrarily on February 8, the number of roosting crows at Docho decreased drastically and roosting individuals at
Maruyama increased. The Sapporo Snow Festival
held on that day at Docho was probably the cause ofthis abandonment. Continuous drum performancesand many tourists walking under roost trees were
probably enough of a disturbance for the crows toabandon the site. Crows which had assembled near
Docho were observed flying off in the direction of
Maruyama. The Docho roost was practically abandoned after February 8, with less than 50 crows roosting after that day. This roost was usually abandonedin late January to February in other years as well,although the decrease was usually a more gradual one.
It seems that the Snow Festival’s coinciding with the151timing of abandonment resulted in the unusual sudden
abandonment. These observations showed that the
number of roosting crows at a site was influenced byhuman activities and that crows switched from a disturbed roost to less disturbed ones.
Figure 3 shows the proportions of jungle andcarrion crows roosting in the Sapporo area from
November 2002 to early March 2003.
From
November to January, the proportion of jungle tocarrion crows was approximately 55% to 45%.
During these months, jungle crows were slightly more
numerous than carrion crows. In February andMarch, the number of assembling carrion crows
decreased after the abandonment of the Docho roostand that of jungle crows increased, resulting in ajungle : carrion ratio of about 2 : 1. It is interestingthat while the population sizes of the two specieschanged, the total number of crows stayed constant ataround 8,500 until March.
The Docho roost was occupied mostly by carrion
crows (over 80%). The other roost sites were
occupied predominantly by jungle crows (70 to 90%).
2.2 Roadside census
To determine the temporal and spatial distributionof jungle and carrion crows in the Sapporo area, I
conducted an automobile roadside census twice amonth from November 2002 to February 2003 andonce in the first half of March 2003. Using the meshmap of Hokkaido published by the Ministry ofEnvironment, I divided the area into 2 × 2 km grids
and set up a route so that it covered every grid. As the
distance covered was different from grid to grid, thenumbers of crows found in each grid was expressed as
the number of crows per kilometer.
The total numbers of crows recorded during thecensuses changed as indicated in Fig. 4. This pattern
was similar to the changes in the numbers of crows
assembling at the winter roosts (Fig. 3). Figure 5

Numbers ofJungleNumbersof Assembling
AssemblingCarrion
carrionand
andjungleCrows
crows
9000

Number of individuals

Numbers of carrion and jungle crows recorded during
road-side censuses
6000

3000

0
１１・９

１１・２３

１２・１４

１２・２８

１・１１

１・２５

２・８

２・２２

３・８

Count dateFig. 3

Numbers of jungle (Yellow bars) and carrion crows(Blue bars) assembling at the six winter roost sites in
2002/2003. When differentiation of the two species
was not possible due to a blizzard, their numbers were
estimated based on their average proportions(expressed as thatched) throughout the survey period.
Crows assembled at Jozankei in mid-December are included in Dec. 14 data.

Fig. 4

The total numbers of carrion and jungle crows
recorded during the road-side censuses from
November, 2002 to March, 2003.

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M. TAKENAKA

shows that the distribution and abundance of thecrows in the census grids changed considerably
throughout the study period. Most of the crows
found during the roadside censuses were either foraging or near potential food sources. Therefore, seasonal and spatial changes in distribution patterns ofboth jungle and carrion crows may well be a reflectionof their movement to better feeding grounds.
Changes in the distribution patterns were not thesame for jungle and carrion crows, indicating thatthese species tended to utilize different feeding
grounds. For example, in November, the largest
number per km-grid of carrion crows was recorded in
the areas where rubbish dumpsites are located, while
jungle crows were found to be more numerous indifferent areas during the same month. In January,
carrion crows were the most abundant in the grid,
which included rivers and riparian woods and were
found to forage near water and in shrubs, while jungle
crows were more numerous elsewhere.

3. Crow Problems – or Human Problems?
3.1 Crows and garbage
3.1.1 Downtown garbage depots
The downtown pleasure center of the city,
Susukino, attracts citizens and tourists alike with its
array of specialty dishes. An enormous amount ofleftover food and other food scraps is deposited along
the streets and alleys awaiting to be picked up by
garbage collection trucks.

When I started observing crows in the Sapporo
area in 1989, garbage in downtown Sapporo wasplaced out with almost no protective measures against
crows. As soon as garbage bags were deposited, aswarm of crows, mostly jungle crows, would alightand feast on fish, meat, tempura and other gourmet
food by pecking open plastic bags or cardboard boxes.
Some stores and restaurants did not even care to put
garbage in plastic bags or boxes and left it exposed.
As soon as the crows began to feast, the streets would
become filled with torn plastic, paper, and raw rubbish.
This scene was repeated every morning (Fig. 6a).
In 1991, a tourist from Honshu wrote a criticalcomment on the mess made by the crows in Susukino
in a local newspaper, claiming that it was a shame forone of the nation’s renowned tourist attractions tohave no preventive measures against crows. This led
the Sapporo municipal government to stipulate measures to prevent crows from feeding on garbage in
downtown areas. The Susukino entrepreneur community association also began to seek ways to prevent
crows from messing up garbage.
The public corporation funded partially by the cityand specializing in garbage collection in commercial
areas, changed its collection schedule so that ideallymost of the garbage would be collected before dawn;that is, to complete collection before the crows left
their roosts. The government also changed its municipal ordinance on the construction of new commercial buildings and composite housing. Under thisrevision, the provision of in-building and/or on-thepremise garbage depots became mandatory.

Carrion crow

Jungle crow

Number of crows/km

Fig. 5

Examples of temporal changes in distributions of carrion and jungle crows in the
Sapporo area. Circles indicate the grids in which municipal and industrial dumpsites
are located.

Crows Problems in Sapporo Area

The Susukino entrepreneur community association
recommended their members either to put garbage inlarge lidded plastic buckets, to cover plastic bags
tightly with sturdy plastic sheets or cardboard, or tokeep garbage inside until the collection truck arrived.
These changes were effective in improving thesituation to a considerable extent. The number ofcrows observed in Susukino dropped by 80% to 90%
after the introduction of the new collection scheduleand the proper protective measures (Table 2). However, the community association has to rely on voluntary cooperation from the entrepreneurs and has notbeen able to obtain 100% cooperation. This seems tobe the reason they could not minimize the number ofcrows completely.
Nevertheless, the case in
Susukino shows that implementation of some preventive measures is effective (Fig. 6b).
3.1.2 Residential garbage depots
Garbage collection in the Sapporo area is municipally operated. Flammable waste (discarded foodand foodstuff, and other organic material, such as
fallen leaves, branches, and non-recyclable paper) iscollected twice a week.
There is a wide spectrum in the manner of garbage
depot management among the residential areas.
To clarify the relationship between the levels ofprotection and messes made by crows as well as thenumber of crows near the garbage depots, theJapanese Wild Bird Society Sapporo Chapter and I
conducted a residential garbage depot survey from
December 2002 to March 2003. A one-kilometer
census route was selected at each of the seven survey
sites. The locations of garbage depots were plottedand numbered on the map.
The census route wassurveyed once a month on the flammable garbage
collection day and data were recorded on the following: whether rubbish depots were protected or unprotected against crows and the protective methods,
the condition of the plastic garbage bags, the extent of
the mess made by crows and the number and speciesof crows present within 25 m and 50 m of each depot.
When possible, information on how residents worked,
or did not work to discourage crows from messing up
the garbage was obtained by interviewing neighbors at
depots during the survey.
Most of the depots were protected against crows
Table 2

153

by covering them with nylon nets, with or without
plywood boards surrounding the garbage bags. Initially in December, 109 depots were protected against
crows with nylon nets (90.1%). The proportion ofprotected depots increased during the survey, becoming 92.3% in March. However, the proportion ofprotected depots varied among the survey sites (Fig.
7a). The usage of nylon nets also varied among them.
This figure also shows the number of unprotected andimperfectly protected depots and the total number of
those messed up by crows, illustrating that crows

(a)

(b)
Fig. 6

A garbage depot scavenged by crows in Susukino in1991 (a) and a typical depot which was madeinaccessible to crows after 1994 (b).

The number of crows observed in Susukino. Rows colored yellow indicate the years before early morning
collection was implemented. Those colored blue indicate the years after early morning collection, including
a pilot operation in 1993.

Date
early morning, 1991-92
4:30 am, 5/18/1991
6:30 am, 1/23/1992
early morning, 1993
6:00 am, 5/15/1994
6:00 am, 10/15/1994
6:00 am, 11/24/1999

Observed number
200-300
500-600
300-500
100-150
200
50
50-60

Researcher
Sapporo Environment Works Corp.
M.Takenaka
M.Takenaka
Sapporo Environment Works Corp.
M.Takenaka
M.Takenaka
M.Takenaka

154

M. TAKENAKA

messed not only the unprotected depots, but also
almost an equal number of protected ones. The
higher the proportions of protected depots were, thefewer were the incidences of crows getting access tobags and making mess (Fig.7b,c). This means thatonce crows learned that there were a substantial number of unprotected depots, they stayed there longer
and managed to get access even to protected ones. In
fact, fewer crows were observed to stay near garbage
depots in the survey sites with higher proportions ofprotected depots.
At the Nakanoshima site, one of our surveyors
interviewed a woman living near an unprotected depot
which was constantly messed up by crows. According to the woman, only three households in her
neighborhood had paid the annual block fees and theblock association would not provide protective nets
for the depots used by those who did not pay the fee.
She said that residents near the depot would not pay
the block association fees and would put out theirgarbage when they were not supposed to. She added,“Why should we pay for their nets?” At the
Maruyama-Nishimachi site, a man told the surveyor
that his association had decided to make their garbage
depots inaccessible to crows and began putting plywood boards around the garbage bags just recently.
He said that this additional measure was proving

effective. It is possible that the considerable numberof crows observed at this site were those still attached
to and lingering in the area. Differences in garbage
depot management seem to reflect the coherence anddegree of cooperation among different neighborhoods.
In Sapporo, as in other Japanese municipalities,
several dozen to over a hundred households in aneighborhood are grouped together in a “block association,” to which each household joins on a voluntarybasis. This block association collects an association
fee from each household, which is to be spent for thewelfare and improvement of their block area. The
pooled association fees are often used to purchaselarge nylon nets to cover garbage bags at the depots toprevent crows from getting access to them. Thus,
effective protection of garbage depots against crows
depends on how much each block association can
allocate for purchasing protective devices such as
nylon nets. In block associations in which the member households are fairly stable with few families
moving in or out, neighbors have a strong sense of
belonging to the community and cooperate with eachother in preventing crows from messing up theirgarbage. On the other hand, in neighborhoods with aconstant influx and out-flux of residents, suchcooperation, including the collection of block association fees, is not easy to obtain.

32

Number of garbage depots

fully protected

imperfect

unprotected

24

16

(a)

8

0

D J F M

DD JJ FF MM

D J F M

D J F

D J F MD J F MD J F M

Nakanoshima

Naebo

Shinkotoni

Minami 6-jo

Fukuzumi

MaruyamaNishimachi

Ishiyama

12

Number of garbage depots

protected
imp&unpro

(b)

Mar

Jan

Feb

Dec

Mar

Jan

Jan

Feb

Dec

Jan

Mar

Feb

Dec

0

24

unidentified
CCJC

Number of crows

18

12

(c)

6

0

Nakanoshima

Fig. 7

Naebo

Shinkotoni

Minami 6-jo Fukuzumi

MaruyamaNishimachi

Ishiyama(a) Proportion of protected depots and imperfectly protected ones at each survey site.
(b) Numbers of garbage depots scavenged and messed up by crows.
(c) Numbers of jungle and carrion crows found within 25m of garbage depots at each survey site.

Crows Problems in Sapporo Area

3.1.3 Municipal and industrial rubbish dumps
As mentioned in the previous section, flammablewaste is collected twice a week in residential areas in
Sapporo. It is burned completely to ash in the incinerating plants in almost all the municipalities in the
Sapporo area. The original mass is reduced to one
tenth by incineration. Incineration is vital for the
longevity of dumpsites with limited capacity.
Plastics, aluminum, and steel are collected once aweek and recycled in various ways. Non-recyclable/
non-flammable waste is collected once a week anddumped as is in the rubbish dumpsites together withash. Currently, there are two such dumpsites inoperation, located near the city borders.
In addition to these dumpsites, the city has several
industrial waste dumpsites to which industrial waste
designated by law must be brought and contained.
This type of waste includes sludge from water purifying plants or soil which may have undergone industrial/chemical treatment.
Crows are attracted to these municipal and industrial dumpsites in great numbers. The residents aroundthe dumpsites regard crows as a nuisance, because
they are noisy, mess up garbage depots, and stain
laundry and painted roofs with their droppings. As ameasure to curb the number of crows attracted to thedumpsites, the city has captured them in traps andkilled as many as 6,000 individuals annually(Takenaka, 1999).
It is interesting that many crows are attracted to thedumpsites, despite of the fact that what is brought into
the sites consists mainly of ash, metal, and plastics
with very little raw rubbish such as leftover food orbits of edibles. On the other hand, dumped nonflammable/non-recyclable waste sometimes contains
such items as mayonnaise containers and tuna canswith some edible portions. Although several crows
may be observed feeding on these scraps, such small
scraps are probably not what the majority of crows at
the dumpsites are after.
As soon as garbage trucks unload ash and bullTable 3

155

dozers spread it over the dumpsite, many crows alightand start to eat it. I observed on a number of occasions that as many as 50-100 crows landed on theash-covered ground of a dumpsite, apparently picking
up chunks of ash.
To understand the characteristics of the crows
attracted to the dumpsite, I collected dead crows(99.2% carrion crows) trapped and killed at the
Yamamoto dumpsite from 1991 to 1992. In addition,
I analyzed the mineral contents of ash from thedumpsite and rowan berries, a common fruit eaten bywild birds in the Sapporo area, including crows, forcomparison. Figure 8 shows a change in the sex
ratio of carrion crows captured at the dumpsite fromthe autumn to spring. The Male to female ratio was
1 : 1 in October and April samples, but 1 : 2.7 inwinter samples. This suggests that more females
visited dumpsites and ate ash than males in winter.
Table 3 shows the proportions of elements andcompounds contained in rowan berries, and the ash
sample from the Yamamoto dumpsite. Calcium
comprised 11.7% of the ash by weight. The ash wasrich in minerals, including calcium, particularly
needed for egg production (Tilgar et. al., 2002). The

Fig. 8

Sex ratio of carrion crows captured and killed at the
Yamamoto Dumpsite.
The sample size for each month is indicated in theparentheses on the x-axis.

Proportion (%) of various matter and elements in Rowan Berries and Ash collectedfrom the Yamamoto dumpsite. Soluble non-nitrogenous matter is an equivalence forcarbohydrates.

compounds and elements
Rowan Berries
Water
60.7
Soluble non-nirrogenous matter
32.7
Crude protein
1.4
Total nitrogen
Crude fat
0.6
Crude fiber
3.4
Crude ash
1.2
phosphorous
calcium
sodiumpotassiummagnesium*Analyzed by Japan Food Research Laboratories

Ash from dumpsite
21.2
0.1
0.78
11.7
2.14
0.63
1.1

156

M. TAKENAKA

contents of other minerals such as sodium, potassium
and magnesium were also relatively high. On theother hand, the crude ash in rowan berries, in which
all of these minerals were presumably present, wasonly 1.2% of the wet weight. The calcium content of
the ash should be much higher than that of other fruits,
which comprise major food items for crows during
winter, as the crude ash contents of most other fruits
are believed to be less than a few percent (Japan
Science and Technology Agency 2003). Thus, more
female carrion crows than males were possibly
attracted to dumpsites toward the onset of breeding
season to obtain calcium from the ash.
Changes in the number of crows captured from1987 to 1998 are shown in Fig. 9. Despite of the factthat both the number of dumpsites and crow traps
stayed almost the same throughout these years, thenumber of captures increased particularly after 1993.
This coincided with the year when crows started tooccupy the Docho roost site in winter.
3.2 Crow problems in the breeding season
Both jungle and carrion crows in their breeding
season can become aggressive in defense of their nests.
They may assault people who happen to walk under ornear the nests. The intensities and modes of assaults
vary from coercive behavior (e.g., flying over thehead) to inflicting injuries. Reactions of the people
attacked by crows also tend to vary and to be
subjective. For example, those with a strong fear or
resentment against crows tend to think that they were“attacked,” even when the crow simply flew overthem. On the other hand, those who are indifferent
to crows do not notice even when they are actuallymobbed by crows. Generally, the reaction and feeling of the public is that crows are fearful and dangerous and that their nests must be removed in order
to eliminate imminent danger.
Nest removal in municipally-owned and -managed
areas such as sidewalks and municipal premises isdone by the city upon requests from citizens. RoughFig. 9Changes in numbers of crows captured at dumpsites
in Sapporo. The bars indicate the numbers ofdumpsites and crow traps.

estimates of the number of nests removed by the city
between 1997 and 2002 are shown in Fig. 10. Because the city did not keep accurate statistics on nest
removal operations prior to 2000, there is no way oftelling whether the number of removed nests increased
over a longer period of time. Nests removed byother parties, such as the electric company and theprefectural government are not included in thestatistics. However, as the city’s removal operations
extend over the entire city, it is still a fairly good indication of general trends for nest removal in Sapporo
since 1997. The number of nests removed uponrequest by citizens seemed to have increased at least
during the past several years. Although the government has not yet announced the exact figure officially,
it is estimated that more than 600 nests were removed
in 2003.
There seems to be a kind of “vicious cycle” between nest removal and assaults by crows. That is,when humans take away the nests, the crow pairslearn that humans are enemies to their eggs and nestlings. It is often the case that, after their nests havebeen removed, nesting crows mob and attack those,particularly men, in certain attires, either identical orsimilar to the work clothes of the nest removal
contractors (Hayakawa & Nakamura, pers. comm.).
From a human standpoint, repeated attacks by crows
give a stronger impression that nesting crows are infact dangerous; therefore, their nests must be removed.
The vicious cycle of escalated aggression by crows
and people even more convinced of the necessity ofnest removal starts to roll.
Of the ten wards of Sapporo, those in which nest
removal is frequent tend to have more incidences ofassaults by crows in the breeding season (Nature
Conservation Section, Sapporo municipal government,
Hayakawa, pers. comm.). On the other hand, theareas where nests are seldom removed tend to havefewer and less aggressive crows.
Three to five crow pairs (both jungle and carrion)
nest on Hokkaido Tokai University campus every year.

Fig. 10

Rough estimates of crow nests removed by the city
upon request by citizens from 1997 to 2002.

Crows Problems in Sapporo Area

Their nests have never been removed since 1989.
The crows may nest by the students’ paths or open rest
areas where students often sit on benches and chat.
The breeding pairs do not seem to care much abouthuman presence and no one has been assaulted so far.
The local block association often requests the university to remove crow nests from the campus, claimingthat crows mess up garbage depots and are “dangerous” as they may attack people. If the university
accepts the request and starts removing the nests, it ispossible that crow pairs which learn humans are
dangerous will begin to assault the students andneighbors.
We should look at yet another factor possibly
involved in frequent assaults by crows. That is, thecrow pairs which nest in highly urbanized downtown
areas, such as Susukino and Odori, seem to havedifficulty securing the safety of their fledglings.
Everywhere around the nest is a paved or open turfarea with no shrubs or foliage. Such settings aroundthe nest may increase the chance that the fledglings
will fall on the paved ground or turf, making themmore susceptible to human intervention. This, in turn,makes crow parents more nervous. According to thecity officials in charge of crow problems, both thenumber of young crows fallen from nests and held incustody by the city and that of reported assaults bycrows were always the largest in such settings.

4. Coexistence with Crows in the Sapporo
Area—What should be done to make it a
success?—
4.1 Sapporo Municipal Government tackling the
problems
In Sapporo, the Nature Conservation Section of theEnvironment Bureau is in charge of crow problems inresidential and commercial areas, particularly nest
removal operations. They have been aware that capturing and killing the birds or removing eggs andnestlings were not effective measures in curbing theincidence of friction or the number of crows. The
Sanitation Section, in charge of trapping crows at
dumpsites, is also aware that capturing and killing are
not effective. For example, the workers at the
garbage dumpsites say, “The number of crows does
not seem to decrease even though we capture several
thousand every year.”
As described in the previous sections, the numberof crows assembling at winter roosts did not change
greatly (Fig. 2, Table 1). This means that elimination
practices were probably not so effective in reducing
the number of crows. The municipal government has
decided to conduct a series of surveys and studies tounderstand the basic ecology and behavior of crows aswild bird species. These will include studies toclarify how and in what circumstances friction between humans and crows can occur, which is expected
to facilitate coexistence with crows with less friction.

157

The Sanitation Department funded local communities
50% of the cost of nylon nets to cover garbage bags
until 2002. As the percentage of netted garbage
depots in residential areas exceeded 90% by the end of
the fiscal year 2002, the funding program ended thatyear. However, the department continues to recommend the use of nylon nets and mediate theirpurchase.
In 2002, they conducted a garbage depot survey toassess the extent of crows scavenging on garbage andthe effectiveness of various types of coverings. The
results demonstrated that netted garbage depots surrounded with a circle of plywood boards connectedwith string (Fig. 11) could effectively deter crows
from pecking through garbage bags. The plywood
enclosure seems to isolate garbage from crows
physically. Starting with the fiscal year 2004, the sanitation department will distribute brochures recommending citizens to deposit garbage bags in the collapsible plywood board enclosures topped with nylon
nets. Similar types of enclosures have been used inmunicipalities in the Tokyo area (Kurosawa et al.,2002). As Matsubara (2003) reported that covering
garbage depots with nylon nets altered the behavior
and home range of a pair of jungle crows, making
garbage depots unattractive to crows should graduallypush their home range out of undesirable areas.
The city ordinance on garbage disposal states that
it is the responsibility of Sapporo citizens to put out
garbage on designated days. Although violation of
the ordinance is subject to penalty, effective enforcement has not been achieved. One of the reasons isthat the violators have to be caught “red-handed.”
So far, the city does not have the surveillance system
to catch and penalize them and/or to track them down
by looking in the garbage bags for identifying evidence, except for serious violations.
4.2 Increased citizens’ awareness for solving crowproblems in the Sapporo area
Although a proportion of Sapporoites are either
still blaming crows for the friction between humans
and crows or are completely indifferent to thesematters, many are increasingly aware of the fact thatcrow problems are, in fact, human problems. The
urge to learn about the ecology and behavior of crows
not as nuisance animals but as wild birds is increasing
among these citizens. Between July and November,
2003, I was requested by three different citizens
associations to give lectures on the ecology of crows
and possible ways to coexist with them. It seemed tobe the general understanding of the attendees, totaling
more than 250, that it is the responsibility of humans
to improvise ways to prevent crows from getting
access to garbage and avoid friction in the breeding
season. Many of them realized that the essence ofcoexistence with crows was basically the same as withother wildlife such as the brown bear and the northernfox, both of which are found adjacent to or within

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M. TAKENAKA

their neighborhoods and are often attracted to garbage.
The citizens who have became aware of the fact thatcrow problems are indeed human problems are
expected to educate others and devise methods tomake garbage depots unattractive to crows and findbetter ways to reduce friction with them in thebreeding season.

5. Discussion and Conclusion

(a)

(b)

(c)
Fig. 11

A method to prevent crows from pecking open
garbage bags has proven effective and will berecommended by the Sanitation Department of
Sapporo. Plywood boards spread in a circle in use(a) and (b), and folded when not in use (c).

The number of crows has not increased over the
past several years. However, some citizens have theimpression that it has increased considerably. Whatcan be the underlying causes of this discrepancy?
The population of Sapporo has increased by over
300,000 in the 15 years between 1988 and 2003.
This rapid urbanization might be regarded as one
cause, which resulted in the emergence of crowded
neighborhoods with weaker affiliation to local
communities and weaker ties among residents. As aresult, more crows are attracted to the neighborhoods
where people are indifferent to the welfare andaesthetics of their surroundings. These localized
increases in the sightings of crows may have given theimpression that there are more crows than before.
The other possibility is that frequent news coverage
since 1997 on the expansion of the crow population in
the Tokyo Metropolitan Area may have had a certain
influence on the residents of the Sapporo area suchthat they have the impression that crows are also
increasing in their region. The press covered Crow
problems more than 70 times in the two years between
1998 and 1999 at least in the Tokyo Metropolitan Area
(Kawachi, 1999). More than half of these were alsobroadcast in the Sapporo area, which could translate
as news coverage on crows more than once a month.
The results of a questionnaire survey conducted by thecity revealed, on the other hand, that nearly half of thesurveyed replied the number of crows around theirneighborhood did not change, about 8% of them replied that crow numbers decreased and about 33% feltthat crow numbers increased. Nearly 66% of thecitizens replied that they took much care in disposing
garbage properly as a measure to elude crows. Despite being swamped by news coverage on the expansion of the crow population in Tokyo area, the generalpublic in Sapporo area may have managed to grasp thereality about crows in their surroundings.
The fact that a considerable number of crows are
attracted to rubbish dumpsites, apparently feeding onash, is interesting in terms of the nutritional requirements of birds. However, we need to find ways tocurb the number of crows attracted to these sites, as
they are one of the major grounds on which friction
between humans and crows occurs and the largest
number of individuals has been captured and put todeath, even though the effectiveness of such elimination is doubtful. It is known that the majority ofCrows Problems in Sapporo Area

individuals captured in traps are juveniles (Tamada etal., 1992), which do not contribute much to either the
reproduction of the crow populations or the density ofresidents.
It is particularly intriguing that crows started tooccupy the Docho winter roost site in 1993/1994,
when captures at the dumpsites exceeded 7,000 for the
first time. A large majority found at dumpsites androosting at Docho are carrion crows (over 99% and80%, respectively). This strongly suggests that a
population of carrion crows started to gather andwinter in the Sapporo area after 1993. The fact thatthe Docho roost is abandoned in late January to earlyFebruary, and subsequent decreases in the numbers ofcarrion crows in both the crow counts at roosts androadside censuses (Figs 3, 4 & 5), also suggests this.
It was reported that carrion crows start reproductive
activities in Hokkaido in February (Tamada et al.,1993). They were observed to court and sit by their
old nests as early as January in Sapporo (Hayakawa,
pers. comm.; Takenaka, pers. obs.). Thus, somecarrion crows probably abandoned the winter roosts
around this period to return to their breeding grounds.
So far, few residents living near the roost sites
regard crows as a problem and almost none haverequested the municipal government to scare themaway from their roosting woods. This may be due tothe fact that each site is sufficiently distant fromresidential areas. The Docho roost, the occupation ofwhich began in 1993, is an exception. However, it isfortunately located in a business district of the citywith very few residents. Putting on ample distancefrom human habitation to wildlife habitats may be thebest way to avoid problems. If crows start to occupy
a roost site in the middle of a residential area or invery close proximity, the occupation may immediately
become a problem for the neighborhood. Once thistype of problem arises, it may become extremely
difficult to elicit roost abandonment (Gorenzel et al.,2002).
It is not clear whether the increase in the numberof removed nests is a reflection of an increase in nesting crows in the city or due to increasing numbers ofcitizens with the belief that crow nests had to be eliminated. Both of these factors might be involved. It isalso tempting to speculate that the increased numberof crow nests removed may reflect the influence of
frequent press coverage, because the city officials incharge of crow problems had the impression thatcitizens’ requests for nest removal jumped after
Governor Ishihara of Tokyo declared the prefecture’s“Crow Eradication Project.” However, one needs toascertain objectively how this trend will change as theintensity of press coverage on crows subsides or its
attitude or tone changes.
Because studies on the
distribution and population size of crows in the breeding and post-breeding seasons have not been conducted, it is not possible, so far, to determine whether
or not the breeding crow populations are increasing.

159

Studies on breeding crow populations are necessary
for understanding their population trends and clarifying the reasons some breeding crows become aggressive and assault people. Increased assaults on people
in defense of nests in urban areas have also been reported in other parts of the world (Knight et al., 1987).
Comparative studies on urbanized crows in different
areas within the Sapporo area and among different
regions may be helpful in understanding the mechanism of crows developing aggressive behavior toward
humans.
Sapporo and its neighboring cities, as well as manyother municipalities of Hokkaido, advocate coexistence of urban lifestyle and nature and are proud of
their rich natural landscapes and resources. In thisrespect, the public may have a predisposition forwillingness to find ways to coexist with crows as amember of the ecosystem of their surroundings. Thiscan be an advantage to the region in tackling withcrow problems. Awareness-raising campaigns by themunicipalities may be helpful in facilitating residents
to cooperate in tackling the problems. Citizenorganizations such as bird enthusiasts’ groups are also
willing to participate in promoting the effective andwise ways to coexist with crows in the Sapporo area.
One should also consider the fact that there is awide range of lifestyles and working conditions
among the residents. Some administrative assistancefor those who are unable to dispose of their garbage
on designated days (e.g., those working on night
shifts) may be necessary.
Crow problems in the Sapporo area cannot be
solved overnight. However, the Sapporo municipal
government has started to accumulate basic data on
the ecology of crows and more communities are
beginning to seek ways not to attract crows to garbage
depots. When these activities become more widespread, friction between humans and crows will decrease considerably.
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http://www.city.sapporo.jp/somu/monita/s_mokuji.htm
http://www.city.sapporo.jp/kankyo/ryokuka/HOZEN/crow/top.
htm
http://food.tokyo.jst.go.jp/(Received 7 October 2002, Accepted 20 December 2002)