As we read the creation account, we see that God started out by creating the lowest forms of life on the earth first. This was the plant life. Then He moved on to a higher form of life and created the fish. After the fish, He created the birds. Each subsequent life form was a little more complex and had a higher capacity than the one previous to it.
Plants can do virtually nothing.
Fish are a little more intelligent. Birds have even a little more capacity. They can fly, sing, and seem to have more intelligence than the fish. A fish can just swim around in a tank. Up until this point, the animal life was highest form of life that God had created on the earth.