Why did the chicken cross the road? To get to the other side. Most people know this joke. But recently, some people have been much more worried about how the grizzly bear and mountain lion can cross the road. " Millions of animals die each year on the U. S. roads, " the Federal Highway Administration reports. In fact, only about 80 ocelots , an endangered wild cat, exist in the U. S. today. The main reason? Roadkill. "Eco-passages" may help animals cross the road without being hit by cars. They are paths both over and under roads. " These ecopassages can be extremely useful,so that wildlife can avoid road accidents ," said Jodi Hilty of the Wildlife Protection Society. But do animals actually use the eco-passages? The answer is yes. Paul Beier of Northern Arizona University found foot marks left by mountain lions on an eco-passage that went under a highway. This showed that the lions used the passage. Builders of eco-passages try to make them look like a natural part of an area by planting trees on and around them. Animals seem to be catching on. Animals as different as salamanders  and grizzly bears are using the bridges and underpasses. The next time you visit a park or drive through an area with a lot of wildlife, look around. You might see an animal over-pass ! When the writer says that animals seem "to be catching on" , he means   _  .
animals begin to realize the danger on the road animals begin to learn to use eco-passages animals are crossing the road in groups animals are becoming safer