A group of chimpanzees is walking through the woods, in Guinea, in western Africa. Suddenly they come to a road. What will they do?
What will they do first? Look both ways? Try to dart over? Just keep walking? Chimpanzees are very smart animals, but are they smart enough to treat a road as dangerous, even when there are no vehicles on it?
A study by researchers at Sterling University and Tokyo University found that chimps assemble into a very specific formation when they cross roads. The alpha male goes to the back of the line, other large males go to the front, and the females and children move to the middle.
This is a classic defensive pattern against large predators, with the strongest members of the troop on the outsides, and the weakest ones protected on the inside. Occasionally one male will also break away from the group and walk around on the road, acting as lookout.
It is possible that the chimps see vehicales as predators. At the very least, they see cars, bicycles, and even walking people as potential threats. Whether they actually know, based on personal experience, that a car or bicycle is dangerous, they still get the idea to close ranks, because this is a dangerous place.