175

Daily Change in Spatial Distribution of Jungle Crowsin Urban Areas
Kazuhiro KATOH1* and Takashi NAKAMURA2
1

Experimental Station for Landscape Plants, Graduate School of Agricultural and Life Sciences,
The University of Tokyo
1051 Hata-machi, Hanamigawa-ku, Chiba 262-0018, Japan
2
Parks and Green Spaces Division, City and Regional Development Bureau,
Ministry of Land, Infrastructure and Transport,
2-1-3 Kasumigaseki, Chiyoda-ku, Tokyo 100-8918, Japan*e-mail: aster@tokyo.email.ne.jp

Abstract
Jungle crows (Corvus macrorhynchos) have increased in number in urban areas across Japan,
creating various kinds of problems. In the present study, jungle crows were counted at 33 study plots
located in large open spaces (>10 ha) in central Tokyo to clarify the role of urban open spaces in crows'
daily flying. Three types of open spaces were recognized: ones used mainly for post-feeding rest, ones
used for further foraging and/or temporary rest throughout the daytime and ones used as roosting sites.
Open spaces where people fed doves or homeless cats tended to be categorized as the second type,probably because crows stayed there to get food provided for doves or cats. In the open spaces of thefirst two types the number of crows correlated positively with tree coverage, indicating the importanceof trees as components of crows' day-time habitat.
Key words: jungle crow, open spaces, spatial distribution, urban, vegetation coverage, vegetation
height1. Introduction
Jungle crows (Corvus macrorhynchos) have increased in number in urban areas across Japan,
creating various kinds of problems. Crow attacks onpeople have frequently been reported, especiallyduring breeding seasons, probably because of theirparental instincts to protect their eggs or nestlings(Higuchi & Morishita, 2000; Sugita, 2002). Scattering waste about, many individuals of the species visit
waste dumps in urban areas to forage for garbage(Karasawa, 1988; Higuchi & Morishita, 2000). They
could potentially pose a threat to Japanese native bird
species (Azuma et al., 1996). Their fecal droppingsand noise may pose environmental problems tocitizens.
Similar conflicts in urban areas between crows andhuman beings have been reported from various location of the world. For example, the house crow
(C. splendens) has been regarded as a pest species in
Mauritius (Feare & Mungroo, 1990) and Singapore(Peh & Sodhi, 2002; Soh et al., 2002). The american
crow (C. brachyrhynchos) also causes trouble in urban
areas across the United States (Gorenzel & Salmon,
1995; Gorenzel et al., 2002). Noise and fecal

droppings around their roosting sites were regarded as
the major sources of nuisance. Direct population
control measures such as capture of adult crows, useof poisoned bait or shooting have often failed (Soh etal., 2002). An alternative way to manage thisproblem is altering the landscape characteristics tomake them less conducive for nesting or roosting ofcrows (Gorenzel & Salmon, 1995; Soh et al., 2002).
In Japan, defects in garbage collection systems
have repeatedly been criticized for providing food resources to crows, and are the most important reason
jungle crows have increased in urban areas (Higuchi& Morishita, 2000). Altering landscape characteristics has rarely been regarded as a measure to control
crow populations. While information about crowpreferences in landscape characteristics is essential for
effective landscape design, our related knowledge is
not enough. As for jungle crows in urban areas,
preference in roosting sites is partly understood: theytend to use large wooded open spaces such as large
urban parks, cemeteries, public gardens and shrine
forests as roosting sites (Karasawa, 1987; 1988). It
is also known that they visit the amusement districts inurban areas (e.g., the Ginza district in Tokyo) early inthe morning to forage for garbage put out by res-

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K. KATOH and T. NAKAMURA

taurants, bars, and hotels along streets (Karasawa,1987).
For example, Karasawa (1987) reported that manycrows roosted in the Meiji Shrine forest located near
the center of the Tokyo metropolis. Some of themvisited Ginza (Karasawa, 1987) or Shibuya (Karasawa,1988), which are also amusement districts in Tokyo, inthe morning for foraging. He also reported that after
feeding in Shibuya, the crows moved to Yoyogi Park,
which is a large urban park near Shibuya, to stay till
evening (Karasawa, 1988). It was also reported thatsome individuals stayed in urban open spaces frommorning to evening (Karasawa, 1988).
These
records suggest that urban crows use urban open
spaces as their daytime habitat, though which kinds ofopen spaces they like is remains in question. Katoh
and Nakamura (2001) answered this question partly:
they reported that jungle crows tended to visit small(< 10 ha) urban parks where visitors fed doves orwhere vegetation coverage was rich with evergreen
trees. They did not study larger urban parks, however, so the knowledge is insufficient for effective
landscape planning to manage crow problems.
In the present study, we focused on large (>10 ha)

urban open spaces to survey the spatial distribution ofcrows and temporal changes in the spatial distribution
pattern. When factors controlling the spatial pattern
become clear, they will be helpful in creating effective
landscape designs to manage crow problems.

2. Methods
2.1 Study plots
Censuses of jungle crows were carried out in six
urban open spaces in Tokyo, namely Zoshigaya
Cemetery, Toshimagaoka Imperial Graveyard, Ueno
Park, Yanaka Cemetery, Hibiya Park and the Outer
Garden of the Imperial Palace (Fig. 1). All of these
are larger than 10 ha (Table 1).
In total, 33 study plots were located randomly
within them, but the plots in Toshimagaoka Imperial
Graveyard were located along the border because oflimited access inside the Graveyard. The area andthe number of study plots in each open space areshown in Table 1.
These open spaces are located near famous amusement districts in Tokyo, namely Ikebukuro, Ueno andGinza (Fig. 1).
During the study period, large

Fig. 1 Locations of the open spaces studied.
●: Open spaces studied○: Amusement districts near the open spaces studied

Table 1 Studied open spaces.

Name of open space
Zoshigaya Cemetery
Toshimagaoka Imperial Graveyard1)
Ueno Park
Yanaka Cemetery
Hibiya Park
Outer Garden of the Imperial Palace2)
1)2)Area (ha)
10.6
15.2
53.4
10.3
16.2
29.5

Number of study plots
5
3
10
5
5
5

Total area of this graveyard and the neighboring Gokokuji Temple is shown.
Nijuu-bashi area only.

Nearest amusement district
Ikebukuro
Ikebukuro
Ueno
Ueno
Ginza
Ginza

Spatial Distribution of Jungle Crows in Urban Areasamounts of garbage left on streets until late morning
attracted many jungle crows to the districts every
morning. It should be noted that only a few crows
were observed there after 09:00. The Ikebukuro
district is located near Zoshigaya Cemetery andToshimagaoka Imperial Graveyard, while the Ueno
district is near Ueno Park and Yanaka Cemetery, and
the Ginza district is near Hibiya Park and the Outer
Garden of the Imperial Palace (Fig. 1).
2.2 Bird censuses
At each study plot, censuses were repeated fourtimes within a day: the first one was done between
06:00 and 09:00 JST; the second, between 09:00 and
12:00; the third, between 12:00 and 15:00; and thefourth, between 15:00 and 18:00. Censuses were notconducted in unsuitable weather conditions: strong
winds or steady rainfall.
At each census the observer conducted a twominute point count. The number of crows and rockdoves (Columba livia) observed within a radius of
20 m from the study plot centre was recorded at eachplot. Individuals flying over the plot were omitted.
The number of doves reflects the degree of feeding byhuman beings (Katoh & Nakamura, 2001). The
observation time, two minutes, was set based on
precedential surveys where the 72% of crowindividuals and the 92% of dove individuals werecounted in the first two minutes of a ten-minute point
count (Katoh & Nakamura, 2001). Observations
were made from the centre of the study plots, but at
the plots in Toshimagaoka Imperial Graveyard theobserver conducted the census procedure outside theplots because of the limited access. All plots were
censused four times (i.e., one day) between November
16 and 24, 1997, and four times between March 8 and
19, 1998.
2.3 Vegetation parameters
Vegetation coverage of trees and that of shrubs andherbs were measured visually at each study plot.
The height of the tallest tree within the bird census
range was measured by Blume Leiss height meter asvegetation height. Relationships between the vegetation parameters and the number of crows in each plot
were analyzed by Spearman’s rank correlation coefficient to avoid being influenced by outliers.

177

3. Results
A total of 623 individual jungle crow detections
were recorded during 264 census visits to the six
urban open spaces over the study period. As theresults obtained in November 1997 and those obtainedin March 1998 showed similar tendencies, we pooled
both data sets before the subsequent analysis.
3.1 Temporal changes in the number of jungle
crows
To recognize temporal changes in the number ofjungle crows in the open spaces studied, percentagesof detections recorded in each time zone were
calculated for each open space. The results areshown in Table 2. Differences in study plot composition among the open spaces prevented us from comparing open spaces according to the average numberof crows per study plot.
The results indicate that in Zoshigaya Cemetery,
Ueno Park and Yanaka Cemetery the majority (64% ormore) of crow detections were recorded in themorning, i.e., between 06:00 and 12:00. We categorize these open spaces as “Type 1,” which crows
visit mainly in the morning. In Hibiya Park and theOuter Garden of the Imperial Palace crows wererecorded rather evenly among the time zones. These
two open spaces are hereafter called “Type 2”.
Sixty-three percent of crow detections in
Toshimagaoka Imperial Graveyard were recorded
after 15:00, indicating that crows used the graveyard
as a roosting site. This is the only “Type 3” open
space in the present study.
3.2 Distribution patterns within the open spaces
At the study plots in the “Type 1” open spaces, thenumber of crows recorded per plot correlated
positively with tree coverage, except in the time zone
between 15:00 and 18:00 when there were few crows(Table 3a). As for the study plots in “Type 2” open
spaces, correlation between the number of crows andtree coverage was also significant (Table 3b). The
other vegetation parameters did not correlate with thenumber of crows, in either Type 1 or Type 2 open
spaces.

Table 2 Temporal variation in recorded number of crows.

Name of open space
Zoshigaya Cemetery
Yanaka Cemetery
Ueno Park
Hibiya Park
Outer Garden of the Imperial Palace
Toshimagaoka Imperial GraveyardTime
06:00 - 9:00 09:00 - 12:00 12:00 - 15:00
52
17
17
33
36
18
41
23
11
30
17
24
22
17
33
6
6
26

15:00 - 18:00
13
13
25
29
28
63

Numbers in the table indicate percentage of detections recorded in the time zone for each open space.
1)
Percentage of detections recorded between 6:00 and 12:00 for each open space.

% morning1)
70
69
64
47
39
12

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K. KATOH and T. NAKAMURA
Table 3 Spearman’s rank correlation between the number of crows and vegetation parameters.
(a) Type 1 open spaces (N=20)
Vegetation
parameters
Tree coverage
Shrub and herb coverage
Vegetation height(b) Type 2 open spaces (N=10)
Vegetation
parameters
Tree coverage
Shrub and herb coverage
Vegetation heightTime
06:00-09:00 09:00-12:00 12:00-15:00 15:00-18:00
0.57
0.47
0.62
0.35
**
*
**
0.16
0.28
0.35
0.20
0.33

0.10

0.31

0.44

Time
06:00-09:00 09:00-12:00 12:00-15:00 15:00-18:00
0.76
0.58
0.64
0.79
*
*
**
0.68
0.24
0.36
0.23
*
0.25
0.10
-0.02
0.21

*: P<0.05, **: P<0.01
N: number of study plots.

4. Discussions
4.1 Roles of urban open spaces for jungle crows
It has been reported that jungle crows in Tokyo
have systems of daily flights (e.g., Karasawa, 1987;
1988). The elements of the system are roosting sites,
feeding sites and temporary abiding sites. We havelittle knowledge about the third element while wehave some about the first two. Though urban open
spaces are possible places for temporary stays, thedetails have not been studied.
The results of the present study suggest that urban
open spaces may act as temporary abiding sites forjungle crows in their daily flight routines. However,
the role is not equal among open spaces: some areused mainly for post-feeding rest (“Type 1” open
spaces); and some are used for further foraging and/or
temporary rest (“Type 2” open spaces).
Differences in vegetation parameters and otherattributes among the types were not clear. Possible
explanations are as follows. Crows tended to visit to
the “Type 2” open spaces in the afternoon to obtain
more food resources. As food provided for doves orhomeless cats by human beings attracts jungle crows
also (Katoh & Nakamura, 2001), open spaces where
feeding of such animals is conducted may be used bycrows for foraging during the daytime. In themorning crows also stayed in the “Type 1” open
spaces where tree cover was provided for their rest but
food resources were not provided. If we can omit
Ueno Park, this explanation matches well with theresults (Table 4). Because Ueno Park is spatiallyheterogeneous and has both (“Type 1” and “Type 2”)
characteristics, this disagreement can occur.
It should be considered, however, that foodsupplies for crows in an open space are not constant.
They can vary temporally because of temporalchanges in the number and activity of open space
visitors. In some open spaces crows may utilize
natural food resources such as fruits, the abundance of
which also varies temporally. Therefore, the type ofan open space may vary, reflecting temporal changes
in food resource abundance. Furthermore, humandisturbance may influence open space use by jungle
crows (Katoh & Nakamura, 2001). Open spaces
where intense human disturbance drives crows away
during the daytime may also be classified as “Type 2”
because there will constantly be few crows in suchopen spaces.
In the present study we selected open spaces nearfeeding sites, which may help us to recognize thepresence of “Type 1” open spaces, i.e., post-feeding

Table 4 Characteristics of the open spaces studied.
Name of open space
Zoshigaya Cemetery
Ueno Park
Yanaka Cemetery
Outer Garden of the Imperial Palace
Hibiya Park
Toshimagaoka Imperial Graveyard
1)

Temporal change patternof crow abundanceType 1
Type 1
Type 1
Type 2Type 2Type 3

Feeding for
doves
No
Yes
No
Yes
Yes
No

Number ofdoves1)
0
15
0
6
5
0

The maximum number of doves (within 8 censuses) was calculated for each plot and the median of thatvalue within each open space was shown.

Spatial Distribution of Jungle Crows in Urban Areas

rest points. If we had studied open spaces far fromfeeding sites only, it would have been difficult toobserve post-feeding concentration.
Katoh &
Nakamura (2001) studied 24 median to small open
spaces that were located apart from large feeding sites
and did not find post-feeding concentration. Therefore the location relative to feeding sites is also an
important factor in determining the role of open
spaces for jungle crows.
Some urban open spaces are known as roostingsites for jungle crows. The present study found thatToshimagaoka Imperial Graveyard is a roosting site.
Other preceding observations also concluded alike(Karasawa, 1988). Denser tree coverage, sparser
shrub and herb coverage and low levels of disturbanceby human beings in the night have been regarded as
essential conditions for open spaces used as roostingsites by jungle crows (Karasawa, 1988). The firsttwo conditions are met in most urban open spaces
while the third is not. Though the third condition
was certainly met in Toshimagaoka Imperial Graveyard, it was also met in the two cemeteries. The
requirements for being used as roosting sites have notbeen clarified enough.
4.2 Open spaces attracting jungle crows
The present study indicates that richer tree cover
may attract jungle crows. This result coincides withobservations in medium to small open spaces reported
by Katoh and Nakamura (2001). The jungle crow is
originally a woodland species (Higuchi, 1979). It is
known that jungle crows tend to nest (Hamaguchi,
1996) and roost (Karasawa, 1987, 1988) in evergreen
tree crowns. It has also been reported that jungle
crows use higher parts of the tree for perching more
frequently than lower parts (Katoh, 1996; Ichinose &Katoh, 2003). Considering these facts it could beconcluded that jungle crows prefer to perch in trees
and to use tree-covered places.
4.3 Suggestions for landscape design
Knowledge of open space characteristics preferredby jungle crows presents an opportunity for landscapeplanners and city officials to make open spaces lessdesirable as rest sites or roosts. Some recent studies
propose landscaping guidelines for such purposes.
Gorenzel and Salmon (1995) recommend using inlandscaping tree species not chosen by crows in thepast as roosts, avoiding tree species (especiallyevergreen trees) commonly used by crows, pruning
trees 7.6 m in height or shorter, keeping pedestrians
and parking cars away from tree canopy that is used
regularly by crows, and pruning evergreen trees usedas roosts to open up the canopies. Soh et al. (2002)
also proposed that tree species used commonly bycrows and other trees morphologically resemblingthem should be avoided, that trees with larger crownvolume, thicker trunks and denser canopies should bepruned regularly, that trees with such characteristics

179

should be checked regularly to detect and remove
crow nests, that roadside trees should be interspersedwith palms or other tree varieties with less desirable
characteristics for nesting to prevent crows fromestablishing large nesting colonies and that the designof bin centres should be improved to prevent crows
from feeding.
These guidelines, however, are proposed for roadside trees, parking, and residential and/or commercial
areas, not for public open spaces. Both these guidelines and the results of current studies support the ideathat trees with dense crowns that tend to be used bycrows should be avoided. On the other hand in
public open spaces such trees are essential for their
scenic beauty and amenity. In general, keeping
scenic beauty and amenity have priority over crowcontrol actions in planting design and management ofurban open spaces. Therefore, we should find otherapproaches considering the relationship between
foraging sites and open spaces. Our proposals are as
follows.
(1) Large open spaces should be located distantfrom larger foraging sites. If the present situation
does not fulfill this requirement, the situation at theforaging sites should be altered by improving garbage
collection systems and bin centre designs.
(2) Feeding animals such as doves and homelesscats should be forbidden in open spaces with abundant
tree cover, or this will provide crows with food resources along with suitable rest sites.
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