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1 .Listen to part of a lecture in an animal behavior class.
1 .Before we leave the topic of animal navigation, let's look at one more species and how it finds its way through its environment.
2 .The species we'll look at is the blind mole rat.
1 .Blind mole rats are interesting in terms of navigation because they live entirely in the dark, in elaborate underground tunnel systems.
2 .So how do blind mole rats find their way around in these complicated tunnels?
1 .Well, for some time we've known that blind mole rats use some combination of two different navigation systems.
2 .Um, one system relies on their sense of time and their ability to remember underground landmarks.
3 .For example, let's say a mole rat wants to find its way through its tunnel system back to its nest, where it sleeps.
4 .Well, it goes along then feels some hard stones or a tree root under its feet, and it basically says to itself, "OK, here's where I took a left"
5 .And then it might remember how long it took to get to the next turn.
6 .And so forth.
7 .The mole rat goes straight or turns based on what it remembers having sensed along the way on previous trips and the time it took between turns.
1 .Now, the other navigation system for the mole rat relies on Earth's magnetic field.
2 .Mole rats have the ability to sense the magnetic field and use it to orient themselves directionally.
3 .But until recently, scientists weren't sure about the role of these two different systems.
1 .Recently, a team of researchers conducted an experiment to answer that question... do these two navigation systems play different roles?
2 .What they did was they designed a special structure that very closely resembles a blind mole rat's tunnel system... which looks like a bicycle wheel... a central hub with multiple spokes radiating outward.
3 .Now, this turned out to be quite important.
4 .Earlier experiments had used a more generic habitat- basically a wide-open circle- which was originally designed to test magnetic navigation in other animals.
5 .That design led to inconclusive results with mole rats.
1 .Now, with their bicycle-wheel tunnel system, the researchers were able to vary the distance that the mole rats traveled between their "nest" and their food source... by creating long routes and short routes.
2 .In each trial, the mole rats started out in their nest, went to the food source, and then had to find their way back home, back to the nest.
1 .To determine which navigation system they were using, the researchers tested the animals under two different conditions.
2 .First the mole rats were tested under conditions of normal magnetism... for both the trip to the food and the trip home.
3 .And under these normal conditions, they all followed their original route back home, regardless of the length of the trip to the food source.
4 .Then, in the second part of the experiment, the magnetic field was altered... but only for the trip home.
5 .A specially constructed set of magnets was used to shift the magnetic field around the habitat 90 degrees eastward.
6 .The researchers wanted to see how the mole rats responded to this shift.
1 .Well...it turns out that the magnetic shift had no impact on the return route of the blind mole rats after a short trip.
2 .They returned to the point where they had started from.
3 .But after a longer trip, they took a totally different route... one that led them 90 degrees east of the nest.
4 .Essentially, they got lost.
5 .This was strong evidence that blind mole rats use magnetic navigation only for longer trips.
1 .So, why two navigation systems- one for long trips and one for short trips?
2 .Well, for now we can only speculate, but we think that when mole rats rely on the first system- using underground landmarks or their sense of time- well they make small mistakes here and there.
3 .On a short trip, this doesn't matter much... the trip is short, so they can't make many mistakes.
4 .But on a long trip, well, there are lots of opportunities to make small mistakes and small mistakes can add up, leaving the mole rat far from where it wants to be.
5 .So on a long trip, a magnetic navigation system is better, more useful, since Earth's magnetic field is stable, constant, a more reliable indicator of direction.