The chicken is said to represent fertility (the whole "chicken and egg" argument notwithstanding). The chicken is symbolic of pride: the first creature to greet the sun, the first to announce thier presence to the world (which, in light of the age-old argument, may be the East's solution to the question: the chicken announced itself, and then bothered to procreate).
However, they also have a secondary symbolism. Chickens are agents of enlightenments in their adulation of dawn. Throughout mythology and folklore, it is always the chicken who represents the break of day; they are the auditory signal that wakes the sleepers, that arrests the intrusion of darkness. How many myths hinge upon the hero being rescued by the sudden arrival of daybreak? How often are the nocturnal monsters sent scurrying into the shadows of the West by the sound of a rooster's cry? The chicken is a transitional creature, one poised on the liminal threshold of change. They must be aware in darkness, for they wake in that time and place and know to look for the light; they are the early worshippers of the enduring cycle of life.
To become a chicken is to ascend the wheel of karma, as it is a more purified creature. When a chicken's head is cut off, its body refuses to recognize death. It fights decay, fights dissolution, fights off the darkness. But, like all flesh, it cannot sustain itself forever. The chicken, in the end, is a symbol of the futility of hope. In the end—of every day, of every life—night comes.