Many have argued over the years that the birds represent the power of nature and mankind's stubborn inability to recognize the power of nature.
Throughout the story, the characters are at the mercy not only of the birds, but also of the wind and sea. Everything seems to work in concert to attack this town. Of course, the characters try to control the situation for their own safety, but they are simply outnumbered and overpowered.
Humans are at the top of the food chain, but that often goes to our heads and we fall into the belief that we can control nature. It is not usually until some natural disaster that we are reminded that we live at nature's will. One landslide, earthquake, wildfire, or in this case, bird swarm, can throw our entire world into chaos. This story reminds readers of mankind's hubris and suggests that even small and normally non-threatening things can become a threat when they act together.