161Soap Storing by Crows

Hiroyoshi HIGUCHI,1* Yasushi MIYAGAWA,2 Emiko MORISHITA,1 Emi KUBOSHIMA,3Hiroshi YOSHIDA,4 Fumio SAKUMA,3 and Yoshihide SHIBATA3
1Laboratory of Biodiversity Science, School of Agriculture and Life Science, The University of Tokyo,Bunkyo-ku, Tokyo 113-8657, Japan
2Yahashira Kindergarten, Matsudo, Chiba 270-2252, Japan
3GEN Corporation, Jinnan, Tokyo 150-0041, Japan
4Department of Environmental Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan*e-mail: higuchi@es.a.u-tokyo.ac.jp

Abstract
Many soap bars have been carried by jungle crows from a Kindergarten in Chiba, central Japan.
We traced the soap bars from the kindergarten by inserting transmitters into the bars, and studied why
the crows took the soap and what they did with it. All the bars carried were found within a radius of
110 m of the kindergarten. Most of them were hidden in fallen leaves on the forest floor. Some of
the bars were moved again to other sites, and were stored again. All the bars traced showed increasing
amounts of damage, suggesting that the crows ate some of the soap each day. Visual observations andvideo images suggest that only a few crow individuals were involved in this soap carrying and storing.
The high number of bars taken suggests that soap has become a favorite food for the crows.
Key words: crows, soap bar, soap eating, soap storing, transmitter

1. Introduction
Some birds, including tits Paridae and crows
Corvidae, are known to store food such as seeds andacorns for later consumption (e.g., Vander Wall, 1990;
Krebs, 1990; Bugnyar & Kotrschal, 2002). Crowsalso store man-made foods such as bread, meat andfried eggs (e.g., Higuchi & Morishita, 1997; NationalScience Museum Nature Education Garden, 2002).
However, we know of no reports of birds storing soap
(cf. Cambell & Lack, 1985; Cramp & Perrins, 1994),
though we have found this to be quite common among
crows in central Japan.
In January 2000, many bars of soap were stolen
from the outdoor washing sites in Yahashira Kindergarten, Matsudo, Chiba Prefecture, central Japan.
About sixty bars were stolen within a three-weekperiod. Because it was not known who was stealing
the soap, a security camera was installed whichshowed that jungle crows (Corvus macrorhynchos)were responsible.
In January and February 2002, we studied why thecrows took the soap and what they did with it. We
did this by inserting small transmitters into several
bars which were then placed in the same washing sites
from which the original thefts occurred. In this paper,

we describe the carrying behaviour, storage sites,
subsequent movements, and the process of soap
eating.

2. Materials and Methods
Every day in late January 2002, we put five to tenbars of white bath soap into red mesh nets hanging
from the water taps at three adjacent basins.
From February 1 to 21, at the same washing sites,
we set out ten bars of the same soap, each containing aradio transmitter, plus one bar containing a personal
handyphone system (PHS) terminal and six bars
without transmitters. Each bar was 75 × 50 × 25 mm
in size, and weighed 90 g. The radio transmitter wascylindrical, 31 mm in diameter, 10 mm high, with anantenna 20 cm long, and weighed 16 g. The PHS isa kind of cellular phone, and we used a special version
named P-Doco Mini, which was developed by NTT
Corporation to trace lost persons (Morishita et al.,2003). It was rectangular, 51 × 34 × 16 mm in size,
and weighed 27 g. The battery life was 3 weeks forthe radio transmitter and 10 days for the PHS. One
bar plus transmitter weighed 85-90 g, which is
12-18 % of the body weight of the crow (500-700 g,Higuchi & Morishita personal data).

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Bars with radio transmitters were traced using areceiver with an antenna, and the soap with the PHS
was traced by the location-searching system of thePHS. Some bars were left where they were found, inorder to track further movements and changes inappearance on a daily basis; this was done until theend of February, by which time all the transmitters andthe PHS had ceased functioning.
The carrying behaviour of the crows was studied
using video cameras. A camera was installed at oneof the three washing sites on February 24, and anothercamera was installed at the house of one of the authors,
1 km from the kindergarten, where we placed bars ofsoap on the house gate in early February. We did not
try to locate the soap taken from there.

3. Results
Crows started taking soap without transmitters on
the fifth day after they were set out in late January.
One or two bars were removed daily during the firstfew days, but after one week the loss rate increased tothree or four bars a day. Some bars with transmitterswere taken the day after they were set out, and all
eleven bars with transmitters and six bars withouttransmitters had been removed by February 21. A
total of sixty bars of soap were taken during thefive-week period of the experiment.
On three occasions, we actually witnessed crows
carrying soap from the kindergarten, and confirmedthat they were jungle crows. Of the eleven bars withtransmitters, eight with radio transmitters and the one
with the PHS were successfully located. All nine
were found within a radius of 110 m from the kindergarten (18.6-107.1 m, 76.7±24.4 sd, n=9).
Theywere hidden in fallen leaves on the forest floor (seven,Fig. 1), in clumps of grass at a construction site (one),and in the garden of a house (one). Each bar was
28.6 to 64.3 m from its nearest neighbour (42.0±12.5 sd, n=9).
We left five of the nine bars where they had beenFig. 1 A soap bar with a transmitter found among fallen leaves
on the forest floor.

found, in order to observe further movements andchanges in appearance. Four of these were moved to
1 - 3 other sites, all within 110 m of the kindergarten,
and were stored again (Fig. 2). The range and mean
distance (m) between these sites were 4.3 to 67.9 and27.2±24.0 (n=8), respectively. All five bars showed
increasing amounts of damage, suggesting that thecrows ate some of the soap each day (Fig. 3).
The video camera at the kindergarten showed thatcrows perched on top of the water tap, pulled up thenet using a foot, and then tore it open using their beakwhile still holding it with a foot (Fig. 4a). When thesoap fell from the net, it was picked up in the beak andcarried away (Fig. 4b), the whole operation taking
only 32 to 45 seconds (40.8±6.0 sd, n=4). Anothervideo camera at the author’s house showed that crows
gnawed off small fragments of soap and ate them insitu before carrying away the rest of the bar.

4. Discussion
In many aspects, the soap carrying behaviour issimilar to normal food storing behaviour in crows.
In both behaviours, individual objects are usuallystored separately at specific sites, and are covered
with leaves and stones (Higuchi & Morishita, 1997;
2000). Second, the objects are eaten during thestoring period. Third, abundance of objects (e.g.,Fig. 2 Locations and movements of soap bars that were carriedby crows from Yahashira Kindergarten and were detectedby transmitters.

Soap Storing by Crows

walnuts, garbage or soap) stimulates the behaviour.
Fourth, objects are sometimes moved from one
storage site to another. In Yokohama, central Japan,
a carrion crow (C. corone) was observed at a storagesite eating part of a piece of bread attached to a stone,
it was then seen carrying the stone with bread toanother storage site (Higuchi & Morishita, 1997).
However, the storing and eating process of normal
food has not been studied in crows as thoroughly asthat of the soap storing in the present study, nor havetransmitters been used.
It is not known how many crows took the total of
sixty bars of soap. However, visual observations andthe video images suggest that only a few individuals,
regularly observed in the area, were involved. The
high number of bars taken suggests that soap has
become a favorite food for the crows involved. Soap
contains higher fatty acid, which is made from naturalor synthetic oils and fats. Oils and fats are also
contained in such foods as meat and mayonnaise,
which are preferred by crows in urban areas (Higuchi& Morishita, 2000; National Science Museum Nature
Education Garden, 2002). It is likely that crows eatsoap in pursuit of nutrients associated with fats andoils.
We know of no published reports of crows eating
soap (cf. Cambell & Lack, 1985; Cramp & Perrins,1994). It is unclear why this behaviour is limited toFig. 3 Process of soap consumption by jungle crows (blackareas). This process was tracked by daily observationsof bars of soap containing transmitters. Both sides of
two example bars are shown for each day. The antenna
can be seen projecting from the soap. The numerals
visible on the bar constitute the ID number of each piece.

163particular areas such as the kindergarten in Matsudo
and the surrounding area. One possible reason is thatsoap is readily available outside at the kindergarten(for children to wash their hands), a situation which is
not common in most areas. Sadakatsu Kunitake(personal communication) has informed us that soap isoften stolen by crows at archaeological excavationsites, where it is available outside. Reiko Kurosawa(personal communication) has informed us that crows
often visit a car-washing site in Kanagawa Prefecture,
central Japan, to peck semi-solid soap from a can;many beak marks can be observed in the semi-solid.
Moreover, we happened to see a crow storing soap on
the campus of the University of Tokyo in February
2003. These observations suggest that soap is afavorite food of crows and is often eaten whenavailable.
Soap is suitable for storage because the individual
bars are often big enough to provide a significant
amount of food and can be stored for a long time.
We plan to use long-life transmitters in the near future
to study the length of time that individual bars arestored. We also plan to study the distribution of soap
storing and eating behaviour among crows.

Fig. 4 A jungle crow perches on a water tap, tears open a meshnet (a), and then holds the fallen bar in its beak (b).

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Acknowledgments
We thank the staff of Yahashira Kindergarten for
helping with this study in various ways, and Sadakatsu
and Yoko Kunitake and Reiko Kurosawa for information on soap carrying or eating in crows, andChristopher M. Perrins for comments on the draft.
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(Received 3 October 2003, Accepted 2 December 2003)