What do the actions of the birds and butterflies say about nature's reaction to war?

The reactions of the birds and butterflies alludes to the fact that in nature..... all goes on. Nature doesn't step aside for the act of war..... life goes on.

One morning two butterflies play in front of our trench. They are brimstone-butterflies, with red spots on their yellow wings. What can they be looking for here? There is not a plant nor a flower for miles. They settle on the teeth of a skull. The birds too are just as carefree, they have long since accustomed themselves to the war. Every morning larks ascend from No Man's Land. A year ago we watched them nesting; the young ones grew up too.