Beavers build many dams, but why?

In an earlier post I pointed out the complex structure of beaver dams and the many decisions that the beavers have to make in building them. there is another complex aspect to beaver dams and a scientific mystery as well. Beavers build many dams, but why?

Most people know that the beaver builds a dam, which creates a pond, and in that pond they then build a sturdy lodge with an underwater entrance. This lodge becomes the beavers home, usually occupied by a mating pair, where they raise a family.

What is less well known is that the beaver pair also build other dams nearby, sometimes a lot of other dams. Why the do this is not well understood, but I have a conjecture about the reason. More on that in a bit.

Two examples will help. In one case we saw the beavers had built five dams in a row on a steep mountain stream. These dams were massive, each almost six feet high. In another case a pair of beavers started building dams on two small side streams that were close together. They built 36 dams in all, mostly relatively small one's.

In both cases the beavers also built their customary lodge in one pond, but why go to the extraordinary extra effort of building all those other dams? Not only does this take effort but it is dangerous.

The beaver has to leave the safety of the pond to get the wood to build a dam and during that time it is exposed to predation. The more dams it builds the further it has to go, and the more time it spends exposed, greatly increasing the danger. Why do this I wondered?

When I looked into it I found that this behavior was well know but the only explanation offered was that the beaver could not stop building dams. In other words all this dangerous activity was an irrational compulsion.

To me this explanation was unacceptable because evolution could easily modify this behavior. There had to be a good reason for building all these dams. The basic principle is animals do what they do for good reasons.

My conjecture is that these extra dams clear land in what would otherwise often be dense forest. Moreover the first trees to grow after the cleared land dries are often aspen and alder, which are the beaver's standard food sources. Thus if I am correct then the beavers are tree farming, not for themselves but for future generations. I would be interested other possible explanations.

The basic point is that animal behavior may be complex and subtle, and hard to explain, but it is unlikely to be irrational on a large scale.

Our Observatory

Our home and offices are set up to watch the horses so we call it the observatory. It is situated on a rise overlooking one of the pastures and with a clear view of the other. We spend several hours a day specifically watching the horses and keep tabs on them the rest of the time, watching closely if something interesting happens.

There are seven horses in the herd, a combination of tennessee walkers and rocky mountain horses. They range in age from five to thirty and all but one are geldings. We do not ride them, in fact we handle them as little as possible, letting them be horses in their own way. There are interesting terrain and vegetation differences in the twenty or so acres they live in.

Of course anyone can watch horses and many people do. The difference is that we are implementing a specific theory of animal behavior, so we are looking for things that others might not see. Our theory and the things we see are discussed in the other posts here in the blog.

The central questions we pursue are what are they doing, what do they need to believe and/or think in order to do it, and why are they doing it? We also spend a lot of time considering why it is so hard to answer these simple questions.

By coincidence there are also a lot of mostly wild critters that we also watch. We are surrounded by a large US National Forest.

Nonverbal thinking is what animals do

Humans do a lot of verbal thinking and this makes it hard to understand nonverbal thinking. Verbal thinking means having words and sentences occur to you. This happens when we talk or write of course, but it also frequently happens without external expression, inside our heads as it were.

The concept of thinking in humans is sometimes limited to verbal thinking, in which case animals do not think. But humans do lots of nonverbal thinking as well and this is what animals do.

Nonverbal thinking occurs whenever there is intelligent behavior. An example of nonverbal thinking in humans is eating a meal, piece by piece and sip by sip, all the while talking about something else. Making the many decision required to eat the meal requires a lot of nonverbal thought. As discussed in the last post, horses also exhibit elaborate intelligent behavior when grazing. This too is nonverbal thinking.

If you watch yourself carefully you will see that you do a great deal of nonverbal thinking as you move about and do stuff. Every action involves multiple decisions.

Moreover you need a great deal of understanding of the world around you in order to do what you do, even to do the simplest things. And so it is with horses and other critters. The challenge is to figure out what the horse or other animal understands, that is, what concepts do they use when they think non-verbally?

For example simply putting on your socks requires knowing what socks are, knowing that you need to put them on, knowing where the are, knowing how to get there, knowing how to select them, knowing how to get them out, knowing where to go to put them on, and knowing how to put them on. That is a lot of knowing and a lot of thinking.

Many things that horses and other animals do are just as complicated as putting on your socks. These actions require a lot of nonverbal thought. The challenge is to figure out what this thinking is and how to describe it, especially the concepts that the critter must have in order to do what they do.

Horses make a lot of decisions

In the last post I talked about how beaver are constantly making local decisions when building their dams. Instinct may give the beaver the knowledge they need to make these decisions but it does not make the decisions for them. Instinct is a way of knowing, not a way of thinking.

The same is true for horses, only the horse's decision making may not be as obvious since they are not building stuff. When they are on their own the horse's number one activity is grazing and they spend many hours doing it. Grazing involves almost continuous decision making because you have to constantly decide which specific thing to eat next.

To see this consider the following thought experiment. You are in a pasture and you pluck a bit of grass. Now you want to pluck a second bit. How many possibilities are there to choose from? Even if you do not move there are a great many, so you have to make a local decision.

People do this too of course, for example repeatedly choosing from the different things on their plate. You can watch yourself do it. What is especially important is that this decision making typically does not involve verbal thinking, so horses can do it too. A lot of thinking is nonverbal.

Moreover, as I described in an earlier post, horses often "graze in motion" which means taking a step or two every few seconds. When to step and where also requires making decisions.

Then there is the fact that the herd as a whole (or in part) often moves more or less together. How this is done is the topic of much scientific research but it clearly involves a great deal of decision making by the horses involved.

Sometimes this decision making regarding what to eat next involves food that is not close by, or even in sight. The entire herd may abruptly go a long distance, into a new field, to graze on some bushes. Or a single horse may do it, leaving the herd behind.

The point is that horses make a lot of decisions as they do what they do and decision making is a form of thinking.

Meet the beaver

My theory of animal cognition began many years ago when my wife and I were studying beaver. I was working my way through grad school by designing earth dams for the US Government. Beavers build earth dams so naturally I was interested.

What I discovered was that a beaver dam is very different from a human dam. In fact a beaver dam is more like a bird's nest. A human dam is a big pile of carefully selected and compacted dirt. A beaver dam is typically a lattice of sticks supporting an upstream face of dirt. One advantage of this design is that it uses a lot less dirt than a human dam does. Another is that it does not wash away when water flows over the top, as human dams tend to do.

Presumably the beaver knows how to build these elaborate structures by instinct. But what I realized while watching them work is that a great many decisions have to be made along the way. These decisions involve the specifics of the local situation, so they cannot be merely instinctive.

For example, knowing how to build a dam does not tell the beaver which stick to use next. Or which tree to fell and how to cut it up to get that stick. Or where to get the next armload of mud. Or where and how to put these items into the structure. These specifics cannot be in the DNA, as it were.

The point is that the beaver must have elaborate sets of concepts in order to perform these elaborate tasks. So do birds and so do horses. It is easiest to see this when we know what the critter is doing. Speaking of which it is an interesting question why beavers typically build many dams in one place, not just the one their lodge is behind. I think I have a surprising answer to this question but that will be another posting.

Horses communicate a lot with posture and gesture

Unlike crows, horses do relatively little vocal communication. Of course they do sometimes whinny, nicker, snort, etc., but this is not the mainstay of their communication. As herd animals they are naturally in close contact, so they rely on what I call posture and gesture for communication.

For example, they make faces at each other, a lot of different faces, each with its own meaning. They frequently push one another, but without touching, by simply approaching in a certain way. They can threaten to kick by reversing, or mock strike with a front foot, or threaten to bite, etc. They can also groom one another, or play the face biting game, etc. Sometimes simply being close by is a form of friendship.

The point is that there is a huge amount of communication going on among the horses. This is easy to miss because humans tend to equate communication with human communication, which is dominated by verbal exchanges, just as with the crows. So-called body language is recognized to occur, but its role in human communication is relatively minor. With horses it is the primary means of communication, and there is a lot of it.

Crows cawing and counting

In the category of other critters one of my favorites is crows. They communicate endlessly while doing things that I do not understand. Part of the problem is that their group behavior is spread over a large area and often hidden in the trees, but even when I can see what they are doing I often do not know what it is. Yet they put a lot of effort into doing it and a lot of communication is involved, so it must be useful. We just do not understand it.

In particular crows know how to count, or rather they have calls that require counting in the sense that a specific number of sounds is repeated. We think of counting as a mental verbal exercise but it need not be. I can decide to take three steps then take them without verbally counting them in my mind. I can also see that there are three horses in the field without mentally verbally counting them.

One of the great obstacles to understanding animals is that we confuse our mentally verbal thinking with thinking in general.

Crows have many different calls, some of which clearly require counting. My favorite call involves two kinds of counting. It is a five caw call that goes caw caw-caw caw-caw. Like Morse code there are timing based pairs within the overall count of five.

But there is also a simple three caw call that is frequently used, and several others, possibly many others. I have never tried to count the calls and I am not sure that I could, because I may not be able to tell them apart.

Note too that what a call means may depend on the situation, or the context as it is called, just as with human communication.

I assume the crows know how and when to make these calls by instinct and they also know what they mean by instinct. But they still have to count when they do it.

Horses do not verbalized constantly the way crows do, but they make extensive use of gesture and posture to communicate. But this is another topic, for another posting.