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My name is Dave Stephens.
I'm a professor at the University of Minnesota.
I have a longstanding interest in the evolution of cognitive phenomenon,
sort of learning and decision making.
And today, I want to talk about a topic that I call Decision Ecology.
And in decision ecology,
we're concerned about how decision making systems reflect the natural world,
the world in which animals live.
And I'd like to start by talking about a specific problem,
which will be kind of the framework around which we'll discuss this problem.
And I want to focus on this particular animal,
this is a pileated woodpecker.
This is a large North American woodpecker,
slightly bigger than a crow.
I don't know if you know how woodpeckers feed,
but we're going to talk about feeding behavior in particular.
But woodpeckers peck wood because they eat the insects that are hidden beneath the bark.
And what they tend to do is fly from tree trunk to tree trunk.
They fly down to the bottom of the tree trunk,
and then they work their way up the tree trunk,
often spiraling up and as they move up the tree trunk,
they are both listening and looking for signs of insect disturbance in the bark of the tree.
And when they see this,
they will dig into it.
They will literally peck the wood.
That's where the name woodpecker comes from.
And they will dig out these insects and consume them.
So it's a pretty amazing phenomenon in many ways.
A sort of, they obviously are sensing
something that humans don't sense when they do this.
They are spectacular animals.
But I want to talk a little bit about the way they exploit their environment.
To do that, let's think about the kind of world that a woodpecker lives in.
So, this is a little wood lot.
And from our point of view,
it's just a tree, but of course,
this is a food pouch from the point of view of our woodpecker, right?
And not only is it a food pouch but there are many food pouches in this environment,
and if an animal has a problem moving around
these food pouches that I want to draw your attention to.
As it moves in the wood lot,
there are two things it's doing.
One thing is it's moving between trees,
and the other thing is it's actually spending time exploiting trees.
And as I told you, it goes starts at the bottom and works kind of
systematically up exploiting these trees and finding insects within them.
I want you to think a little bit about what the implication of this patchiness is.
And by patchiness, I mean that a woodpecker lives in
a world where there is, you know, it's not a uniform carpet of food,
but food is isolated into different clumps.
And this isn't unique for woodpeckers.
This is a feature of the world that animals live in generally.
And so, when our woodpecker enters a clump of food,
you can imagine that there is kind of
a relationship between the time it spends in its pouch,
or in our case a tree trunk,
and the amount it gains from this food patch.
So what typically happens is that at the beginning of time spent in a patch,
the animal is finding food fairly quickly because the patch is fresh.
It's never been visited before,
but as the animal spends more time in the food patch,
the rate at which it finds new items slows down.
So it has this kind of decreasing marginal rate of gain, right?
We call this relationship between time
spent in the patch and the gain, we call it a gain function, right?
And typically, these gain functions kind of bend down like this, right?
And so this happens because the animal's basically using it up, right?
It's exploiting everything that's there or everything it can find.