Why was the Old man the last to leave the town in "Old Man at the Bridge"?

The old man explains to the soldier at the bridge that he was the last one to leave the town of San Carlos (the story takes place during the Spanish Civil War) because he had to take care of his animals. He says he left behind two goats, a cat, and four pairs of pigeons.
He left because a soldier told him it was too dangerous to stay due to artillery fire. The old man thinks his cat will be fine because cats know how to survive, but he worries about what will happen to his goats and pigeons. If the artillery fire is unsafe for him, won't it be so for his animals? He asks,

But what will they do under the artillery when I was told to leave because of the artillery?

The guard reassures him that the birds will fly away since the old man left their cage unlocked. However, the old man is still distressed, and the soldier knows there is nothing he can do for him. The simple humanity of the old man is a stark contrast to the cruelty of war.