Some animals can easily find their way home after a long journey. How do they make it? Scientific research shows that they are born with certain unusual abilities for direction.
A certain kind of ants, for example, can count their steps to avoid getting lost. They can go as far as 110 metres and bring food home. These ants live in the open desert (沙漠), so they have nothing to guide them along the way. It's like someone walking six kilometres through a dark forest.
Some fish have an unbelievable sense of smell. They can smell even a single drop of their home water in a large sea area. Some sea birds have a similar ability. They are able to make a smell map of their flying area.
Some animals can sense the earth's magnetic field (磁场), while humans can't. This magnetic field guides a certain kind of fish when the swim a long way to a place and then back. How can this kind of fish do that? It is still a____mystery. Scientists have no good answers yet.
However, animals with such unusual abilities still have difficulty dealing with environmental changes caused by human activities. For example, many birds depend on stars for direction, but they get lost easily a night when city lights are kept on all night. To solve this problem, we can simply turn off some lights at night. Clearly, one small act of humans may mean a lot to animals.
