Examples of animals, religion, machines, or other things from nature did Stephen Crane use in The Red Badge of Courage?

Different uses of these images by Crane are as follows;

The squirrel, immediately upon recognizing danger, had taken to his legs without ado. He did not stand stolidly baring his furry belly to the missile, and die with an upward glance at the sympathetic heavens. On the contrary, he had fled as fast as his legs could carry him; and he was but an ordinary squirrel, too--doubtless no philosopher of his race.

But at last the guns stopped, and among the men in the rifle pits rumors again flew, like birds, but they were now for the most part black creatures who flapped their wings drearily near to the ground and refused to rise on any wings of hope.

This landscape gave him assurance. A fair field holding life. It was the religion of peace. It would die if its timid eyes were compelled to see blood. He conceived Nature to be a woman with a deep aversion to tragedy.