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HOME >> Nature Interface 2001.3： Special Features >> Tracking the Movement of Crows Using PHS -- What city crows are telling us.
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 Tracking the Movement of Crows Using PHS -- What city crows are telling us. Prof. Hiroyoshi Higuchi (The University of Tokyo) 
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Big cities like Tokyo produce enormous amounts of raw garbage. In Tokyo, as much as 4 million tons of raw garbage is created annually. This huge amount of raw garbage seems to have attracted and contributed to the population growth of crows. The nature of the crow problem lies not in the mere increase in the crows' number, but in the increase in the number of residents. The crows, which have been overbreeding, are smart, and are causing various problems because of their intelligence. In cities, troubles between crows and people do not arise from the crows' behavior as birds. They seem to arise from the crows' lives as they intersect with the lives of humans. The first step to solving these problems is to gain an understanding of the crows' behavior in cities. However, it used to be very difficult to study such behaviors. A remarkable new method of tracking crows has been jointly developed in conjunction with Prof. Kiyoshi Itao (General Editor of Nature Interface). In this method, crows are tracked by PHS's, or "Personal Handyphone System." This article discusses the problems crows are causing in cities, and describes the PHS method used for tracking crows. Difficulties in Tracking the Behavior of City Crows In the conventional method used to track the movements of birds, a label is attached to the foot or the wing of the bird, and the bird is tracked visually by human eyes. In another method, called radio telemetry, a small transmitter is attached to the back of the bird, and the radio signals are monitored by hand-held antennas from different monitoring points. The bird's position is determined geometrically by the directions from which the signals come. These two methods are actually very difficult to apply to studying crows in cities. They even present some dangers to investigators. The buildings in cities hinder visual tracking by the human eye. Once the birds fly over a building, it is no longer possible to track them visually. In the radio telemetry method, radio signals are reflected by the buildings, and this causes apparent radio emissions from completely wrong directions. It is dangerous and difficult for the investigators to keep tracking the crows, because they have to move within the town quickly in order to continue following the crows. We had been facing these difficulties in tracking city crows, and came up with the idea of attaching PHS terminals to crows after learning about position information acquisition using the PHS system. PHS is a kind of mobile phone which is also able to transmit information on the whereabouts of the person who is carrying it. However, he faced another problem in considering using PHS systems on crows - the weight of the PHS terminal. Crows weigh 600 - 700 g (ca. 1.3 - 1.5 lb) on average. The device that is to be attached to them should be less than about 4 % of the birds' weight, or 30 g (ca. 0.07 lb). However, a PHS terminal, which, although light among mobile telephone terminals, still weighed 70 grams then, was twice as heavy as the acceptable weight. The Method of Tracking Crows Using PHS For about a year since I first thought of using PHS system to track crows, I had been struggling to overcome the weight problem. But it turned out that a collaborator able to solve the problem was nearby. That collaborator turned out to be Prof. Kiyoshi Itao of the Graduate School of Frontier Sciences at the University of Tokyo, who had been conducting research on micromachine information technologies. He had created "wearable" equipment, pursuing networks that enabled information acquisition and communication by machines equipped with sensors. These wearable devices had been studied and developed in the Nature Interface Laboratories, directed by Prof. Itao, not only for use in human beings, but also for use with animals. A PHS terminal for crows was chosen as a research topic in the Nature Interface Laboratories, as a new method of utilizing sensors in positioning. Tracking System Using PHS My encounter with Prof. Itao led to their joint study on reducing the weight of PHS's. We eventually achieved a PHS terminal weight as light as 29 grams. A tracking system using a weight-reduced PHS terminal is actually a position detection system. In this tracking system, the position of each PHS terminal is always registered in the communication networks, and the position of the PHS is continuously tracked. In other words, the radio signals from the PHS terminal are received by a cell station, and forwarded to the information center. The position data may be then displayed on a computer screen as map information. The antenna for PHS systems covers only a small area, because the radio signal intensity is weak. Therefore, position registering is possible only when the cell stations are placed from every few tens of meters to a few hundred meters. For this reason, PHS cell stations were placed on electric poles, public telephone booths, building roofs, and every other conceivable place. The position of a crow can be detected with an accuracy of within 100-200 m (110-220 yd), by tracking the position of antennas, which are densely placed in cities. In the first stage of the creation of this system, the Itao Laboratory of the University of Tokyo, Alps Electronics Corporation and Seiko Instruments Corporation started to collaborate to modify the terminal based on the terminal produced by Alps Electronics Corporation, using the infrastructure of DDI Pocket, a PHS service company, to reduce the PHS terminal weight. The first experiment was carried out by these three parties, who received a discount from DDI in their user agreement. In the next experiment, NTT DoCoMo's proprietary terminal, called "P-doko?" for "'where are you?' service," was modified with the collaboration of Seiko Instruments Corporation. A lightweight terminal weighing only 28 grams, which is 4 to 5 percent of the crows' body weight, and would not hinder them in carrying out their daily activities, was achieved. Once a lightweight terminal was developed, the tracking experiments were started. First, they captured the crows, with the collaboration of the Ueno Zoo in Tokyo. A PHS terminal was attached to each crow. The crows were then kept for a while in the zoo, to see how they would react to the sensors. It turned out that, contrary to their prior expectations, the crows didn't seem to dislike having PHS terminals attached to them. The Tracking Started The first tracking started in the fall of 1999, using five crows, each fitted with a PHS terminal. On the first day, all five crows stayed in Ueno Zoo. Tracking can't begin until the crows start to move. On the second day of the experiment, the crows started to fly, and fly far. Ms. Rie Nagato, a graduate student at the University of Tokyo, was watching the computer screen which was part of the tracking equipment, and saw that the crows were moving to the north and beyond. Ms. Nagato called me to ask if she should shorten the communication interval, which was the interval within which the tracking equipment recorded the crows' movements. She changed the interval from 2 hours to 20 minutes. One crow which flew to the north went to Nishi-Nippori, and stayed there (Nishi-Nippori is 2.5 km (1.6 mi) north of Ueno Park.) The crow stayed in the Nishi-Nippori area on throughout the next day. Through this tracking, it was demonstrated that crows fly to distant places. In the tracking experiment conducted in the year 2000, PHS terminals of 28 grams weight were used. Four crows were successfully tracked, and interesting results were obtained. As a result of our tracking experiments, three types of movements in crows were identified, in terms of where they fly to from day to day. Each movement type of crow is described as follows: Three Types of Crows - City type - Old town Tokyo type - Resident type - City Type On the first day of tracking, the crow we later designated a "city-type" crow stayed in the Ueno Park area. Around noon the next day, it flew to a spot near a hamburger shop in Ginza, and then to a beauty parlor in a small lane in Roppongi. After that, it flew at 3 p.m. to an intersection in Akasaka, and then to Roppongi again, and finally returned to its roosting place in Ueno Park. (Note: Ginza, Akasaka and Roppongi are areas in Tokyo, famous for their high-grade restaurants, stylish boutiques and chic shops.) - Old Town Tokyo type The east side of Tokyo is a traditional shopping, entertainment, and residential district. On the first day of tracking, the crow we later designated an old town Tokyo-type crow stayed in the Ueno Park area. On the second day, it flew to the north in the morning, and appeared in Machiya in the Arakawa district of Tokyo at 6pm. Machiya is close to a sewage treatment plant. Surrounding the plant is Arakawa Natural Park, which has small groves of trees. They spent the morning there, and moved to a riverbed near Nishi-Arai Bridge in Adachi Ward later on in the day. Thus, this type of crow moves around in the old town area in Tokyo. The old town-type crows seem to prefer parks and riverbeds. - Resident Type What we later called "settled type" crows remained in the Ueno Park area, although they did move around inside the park itself. They changed their roosting places slightly. On the first day, they roosted near the main gate of the park. On the second day, they moved to a place near Kanei Temple near the Ueno Park. What Can be Known from the Tracking Results Crows move 3 to 5 km (ca. 2 - 3 mi) in a straight line within a day. A distance of 5 km may cover two or three wards. (Tokyo is divided into different areas, called wards.) This means that even if each ward takes action to solve the problems caused by crows, independently of the other wards, the problems won't be solved, because crows are mobile, and often change their roosting places. This suggests that all of the 23 wards of Tokyo, along with the whole of the South Kanto area around Tokyo, need to work together to combat their crow problems. The crow tracking experiments using the PHS system has proven this. Examples of Possible Actions Humans can Take As stated earlier, it is necessary for human beings to take unified actions against the crows. What should we do? We will first consider possible actions to each problem. Then we'll consolidate issues which are common to each problem, to figure out essential solutions. Among the problems that the crows create, the first is their foraging of raw garbage, a problem which everyone in Tokyo has observed. In Tokyo, collecting garbage in the middle of the night (3 to 6am),which has been tried in Jiyugaoka and Mitaka-shi, has proven to be very effective. People rarely saw crows after these two areas implemented nighttime garbage collecting. Using plastic buckets with lids to protect the raw garbage from pecking by crows, has also proven successful. The second problem is the importance of using common sense when a crow attacks a human being. When this occurs, it means there is a nest or a young crow nearby. The most straightforward solution is to remove the nest, but this should be done as a last resort. There are better ways to handle the problem, such avoiding walking close to the crow's nest. Another, more positive way to handle the problem is to stare at the crow, which will prevent it from moving closer, since crows regard a stare as a threat. (Note that if you stare at the crow too long, the crow will become stimulated and ready to fight. Glancing once or twice at the crow, for brief periods, is sufficient to convey a threat.) The third problem we face is when crows place stones on railway tracks. When crows are given a piece of bread, they will often hide the bread among stones. People cause this problem, because we are the ones who give the crows bread. Feeding crows seems like a trivial matter, but may cause a dangerous situation. To solve this problem, we need to be conscious of it. The fourth problem is collisions between crows and airplanes. Collisions occur when crows gather near or in airports. Many airports are built near the ocean, where disposal centers are also built. It is understandable that crows flock near airports. It is important to check the facilities nearby when building a new airport. Crows tend to congregate in areas where the height of the grass attracts insects, which crows capture and eat. Increasing the height of the grass in airports should reduce the number of crows. Finally, blackouts are caused when crows build their nests on steel towers. There are four kinds of actions we can take to solve this problem: we can prevent crows from approaching steel towers, we can prevent crows from building their nests on steel towers, we can protect the insulated parts on the towers, and we can guide the crows to make their nests elsewhere. To prevent crows from approaching the steel tower, there are visual devices that can be used, such as eyeball-shaped balloons, mock-ups of crows, and glittering flying saucers. There are also devices with audio effects which emits explosive sounds such as roaring. To prevent crows from nesting on steel towers, it is effective to place thread-like materials such as flexible wires and fine sticks over the surface of the area crows like to nest in, so that crows can't approach there easily. It is also effective to spray a jellied material there, or to install a plate, so that crows can't build their nests. To protect the insulating parts, it is effective to wrap them with a cover, so that anything that drops from the nest can't fall on and damage them. To guide the crows to make nests elsewhere, it is effective to prepare a basket-shaped stage at the center of steel towers, and let them make nests there. As stated earlier, the problems created by crows may be solved, by and large, by combining to take a variety of actions. However, these are only temporary actions. What actions should we take to lead to an essential solution to this problem? The cause of problems between human beings and crows is that there are too many crows. One solution may be to control the number of crows in the city. However, crows have increased because the raw garbage that human being create has increased. This view must be recognized by both the garbage-creating side of this problem, and the garbage-collecting side. Each regional community must find a wise way of collecting their garbage, and minimizing the amount produced. If the garbage is produced, it must be kept from the crows. If crows are expelled from one region, they just move to another region. Therefore, coordinated action among all of the areas of Tokyo is important. New methods of garbage collecting can be tried. For example, if the garbage can be transported to a disposal plant in a pipeline, the crows will have no contact with it at all. Need of Further Studies A beginning was made in tracking crows by successfully reducing the weight of PHS terminals. This study started because a great number of conflicts are occurring between human beings who live in cities, and crows. Crows' natural behavior is to change and expand the space they inhabit. But we must be aware that such changes may bring about changes in the ecosystem of a city, sometimes drastically, such as when crows reduce the insect population, and at other times rather slowly, resulting in unseen and unexpected changes. A new methodology is being pursued now, in which the possibilities of collaboration between public administration and research fields are expanding. It is possible for more information about the latest advances in science and technology to be used in research, information which hasn't been previously available by conventional observation. The method used to track crows is an example of how we can use new methods to collect and analyze information on animal ecology. Eventually, we'll be able to use this method to retrieve other information on the environment. In the future, much more will be known about animal ecology, including animals' health, behaviors, the velocities at which they move, the rate at which their wings beat, and how they live and die. All of this will be observed using position information, health information, and information on their movements. The development of nature interfacer technology will lead to a nature interface for wild animals. Furthermore, by collecting geographical information, weather information, water quality information, and plant information, comprehensive ecological and spatial information with geographical and spatial environmental information will be accumulated. This comprehensive information will give us the prospects of promoting action on global environmental problems by overcoming the barriers of research disciplines, and by grasping the relations between internal and external causes of phenomena in ecosystems. This means the construction of an N dimension (from 1 to N) environmental information system which Prof. Itao has proposed, and which adds various attribution information to the conventional 2 to 3 map information using GIS (Geographical Information System). カラスの追跡日記 My Memory of Research on the Crows RIE NAGATO (NTT DoCoMo, Inc.) I was the person in charge of monitoring the movement of the crows, after the PHS devices were placed on them at Ueno Zoo in Tokyo. On the first day, I watched the computer screen with great anticipation, but the crows just moved around within Ueno Park. I then thought "It might be better to observe them on the ground." I started to doubt whether the tracing system using PHS was going to be any use. I observed the crows' movement from morning to night on that first day, but there was no change. The battery in the PHS devices would work for only three days, and one day had already passed. I wondered if the experiment would work. After sunset on the first day, I told Prof. Higuchi about the lack of movement of the crows. He said the crows might have been startled to have such strange instruments put on them, and that they weren't going to move. But still, I was disappointed. I went to the laboratory early on the morning of the next day. I was quite surprised to see the monitor. The scale of the map on the monitor had changed! One of the crows had flown a long distance! I was very excited. I immediately called Prof. Higuchi. We felt relieved to see that the PHS devices were useful for tracking crows. The experiment turned out to be a very stimulating experiment for me as a student at the Department of Precision Engineering. In this experiment, I had to catch crows and install PHS devices on them. People say crows are harmful, but I realized crows have fine feathers, and I felt more friendly towards them. More than one year has already passed since then. I still remember clearly the hot summer days when we were bitten by mosquitoes, as we were conducting our study of crows. (1/1)  |
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