Ethograms of Mice

The study of animal behavior starts with a description of behavior. Before we can study how behavior develops, or what causes it, or how it affects an animal's ability to survive and reproduce, we must know what the behavior is. In other words, we must have a thorough description of the postures, movements, sounds, etc. that constitute the behavior, as well as a catalog of the situations (contexts) in which it occurs and the responses it elicits from other animals. Describing behavior can be very difficult, however, so animal behaviorists have developed ways to make their job (and ours) easier. One such way is the use of "ethograms." An ethogram is an inventory of the behaviors of a species, with the behaviors thoroughly described and organized into categories. The ethogram places the animal's behavioral repertoire into an organized structure, which enables animal behaviorists to discover how each behavior helps the animal to survive, to mate, and to reproduce. Ethograms also allow animal behaviorists to speculate about the evolution of behavior because similar behaviors can be compared among species in an evolutionary lineage.

There is no one right way to describe behavior. Two different ways to describe behavior are on the basis of structure and on the basis of consequences. "Structure descriptions" characterize the appearance or physical form of the behavior. In other words, the behavior is described in terms of the subject's posture, movements, and sounds. Think, for example, about how you might describe a handshake in terms of postures, movements, and sounds of two interacting people. Consequences are the presumed effects of the subject's behavior on itself, on its environment, or on other organisms. In "consequence description," the behavior is described with respect to its presumed consequences without paying particular attention to the subject's posture, movements, and sounds. The handshake, which could be described above as postures and movements, could also be described as a "greeting ceremony" in a consequence description.

Categories such as "obtain food" or "escape predators" are descriptions in terms of their consequences. For example, "turn light on" is a consequence description, while "push switch down using index finger" is a description in terms of structure. Consequence description is the more economical of the two methods because it does not require the observer to make subtle discriminations between very complex movements. Subtle discriminations are important, but when first learning how to do ethograms, the structure description may be confusing. On the other hand, without structure descriptions, different workers may end up studying structurally different behaviors with similar consequences. For example, handshakes and "high fives" are both greetings involving the hands, but they occur in different contexts and are often used by different individuals.

A third type of description is "relational" and concerns the organism's spatial relations to other organisms or something in the environment. The focus is on where the organism is or with whom it is, rather than what it is doing.

Categorizing behavior requires very close observation so that accurate ethograms of the species under study can be constructed. This becomes more difficult when the organisms you are studying are members of an unfamiliar species. In order to familiarize you with the construction of ethograms we will start with a common organism, the laboratory mouse, Mus musculus. We will use a checklist for our first observation. This will help us familiarize ourselves with observing behavior. We will then use the "behavior scan" method to construct ethograms of the mice alone and together.

Methods

The mice will be housed in cages and your group will pick one mouse to observe. Remove the mouse from the main tank and place it in another. Remember to be gentle with these animals. They will be frightened because you will be removing them from their known surroundings. Let the mouse explore its new surroundings until it seems calm enough to observe. Keep track of how long it takes, and try to describe how you decide when to start observing.

Initial observation.-Your first observation will last one hour and you will use this time to identify categories of behavior (for example, walking, sleeping, and eating, among others). In these initial observations your goal is to identify and describe categories, and count (quantify) the number of times each behavior is performed. The descriptions need not be complete structure descriptions, but should be detailed enough to allow someone else to identify your categories unambiguously.

First behavior scan.-Your second observation will also last an hour and you will use the behavior scan method and your behavioral categories to construct an ethogram for your mouse. In this method you make a "scan" at regular, brief intervals (say every two minutes) and check off the behaviors that are occurring at the instant you make the scan. The results of the behavior scan method can then be used to construct a "time budget" of behavior (what percentage of time is spent in each category), or to identify the sequence in which behaviors occur. A sample data sheets might look like this (but you'll probably have more categories):

Sample Data Sheet

Second behavior scan.-In the third hour (or next lab period) you will join with another group, place your mice together and observe how they interact. We will pick numbers out of a hat so the mice are grouped randomly. Our first grouping will be pairs of males and the next lab period we then pair two females. Following the completion of the each lab, return the mice to the main holding tank and make sure that they have food and water.

Data analysis and presentation of results.-You will present your results in the form of a group lab report, which should include the ethogram that you constructed. The ethogram data can easily be summarized in a graph as shown in the figure below. Include a discussion of some of the problems you encountered, and possible solutions to them. Use your data to draw conclusions about the duration (how long), frequency (how often), and sequences (in what order) of the categories of behavior you identified.

Things to Think about

Are ethograms an efficient way to learn about behavior? Do you think that observations of animals in a laboratory setting produce valid ethograms? Why or why not? How could you supplement your observations? Are visual observations an efficient way to gather data to construct an ethogram? Would automated recording be possible? What are the advantages and disadvantages of visual observation versus automated recording? What species would you compare to mice using this method to determine if they have evolved from a common ancestor? What would this tell you? Can you think of a better method? What other animals could we observe to construct an ethogram of their behaviors? How could you construct ethograms of human behavior?

Materials Needed

one mouse per group of students (preferably 2­3 students per group) with one or two "spares"cages to house mice between observations aquaria (or large cages, or home-made arenas) in which to do observations water bottles, mouse chow and bedding

Tips for Teachers

Laboratory mice can be purchased from biological supply houses such as Carolina Biological or Nasco, but it is easier and cheaper to buy them at a local pet store. If mice are not available, or if you don't want to use mice, there are several other animals that could be used. Gerbils are a good alternative, but they are not available in some areas of the country, and they are more expensive than mice. They do have several advantages, however. First, because they are desert animals, they are easier to keep. They drink less water, and their cages don't need to be cleaned as often. They are also much easier to give away at the end of the exercise, or to keep in the classroom as mascots. Fish and some insect caterpillars (e.g., the luna moth) are other possible substitutes for mice.

If your students would like to see some examples of detailed ethograms, you can have them look at Baboon Ecology by Stuart A. and Jeanne Altmann (University of Chicago Press, 1970) and The Year of the Gorilla by George B. Schaller (University of Chicago Press, 1964). There are also some excellent films/video tapes that you could show to your class before they do their first observations. A favorite of ours is "Mysterious Castles of Clay" (Survival, Anglia), which describes the behavior and ecology of termites in Africa and has some of the best photography (including scenes inside the mound) we have ever seen.

Before your students begin their observations, have them discuss the concept of an ethogram. Ask them to think about what would be necessary to construct a complete ethogram for a given species. Ideally, a species would have to be followed in its natural environment without any human interference for its entire life span, but obviously this is an impossible task. Ask them to consider the advantages and disadvantages of constructing ethograms on captive or semi-captive or semi-domesticated animals, for example in a laboratory setting as we will use in this exercise. Ask them whether it is ever possible to observe animals without human interference-is there something akin to the Heisenberg uncertainty principle at work? That is, does the act of observing change the situation so that all observations must be of "unnatural" behavior? Suggest to your students that they consider ways to minimize the effects of their presence on the behavior of their subjects. Perhaps they should do their observations from behind some sort of viewing screen.

Let your students come up with their own categories of behavior, and don't try to enforce a common set of categories. It will be interesting and instructive for them to compare across groups later (for example, in the last sets of observations). Be sure that they don't become fixed on the simple, three-category list given in the examples. They should come up with their own categories, and should have more than three. Ask them how many categories would be adequate, and how they would know when they have developed an adequate (versus an exhaustive) list. Above all, give them enough time and freedom from intervention to do a reasonably thorough study. If it seems that they need more time, think seriously about giving it to them.

Finally, you might be wondering what to do with your mice after the students are finished with them. Some students will probably want to adopt them as pets, and that's fine as long as you make sure to get permission from parents. Alternatively, you might know someone with a large pet snake. Many snakes only eat live food, and pet store mice are a common food item. As a last resort, you must consider "sacrificing" (killing) the mice. There are somewhat costly but humane methods (e.g., lethal injection, ether) and there are some methods that don't cost anything, but are not very pleasant for the biology teacher (e.g., cervical dislocation). Of course, you could always keep them as pets yourself, or keep them in school as class mascots. Remember, however, that mice require lots of care, especially frequent cage cleaning. And unless you want lots more mice, do not house males and females together.