Why did the old man at the bridge leave his home in San Carlos?

The old man at the bridge left his home in San Carlos because his town was under attack. In the story, the old man tells the narrator that he was told by the army captain to leave. Apparently, San Carlos was taking artillery fire from the enemy, and it was no longer safe for civilians to remain in town.
The old man was unwilling to leave, however. He tells the narrator that he was the last one to leave San Carlos because he was taking care of his animals. During the conversation, the old man confesses that he has no family; the animals he cared for were the only family he had.
The old man's animal family consists of two goats, a cat, and four pairs of pigeons. He admits that he is afraid for his animals. While the cat will likely stay safe, he is not quite sure the goats and pigeons will survive. However, the narrator assures the old man that the pigeons will likely fly away (provided the bird cages were left unlocked). 
The old man left his home in San Carlos because his town was under enemy attack. Despite his decision, however, he regrets that he had to leave his animals behind.