The imagery of the animals underscores the struggle for the survival because the family is struggling against the odds just like nature.
The roosters fight each other, like Kino’s family has to fight against the elements.
Near the brush fence two roosters bowed and feinted at each other with squared wings and neck feathers ruffed out. It would be a clumsy fight. They were not game chickens. (Ch 1)
Kino’s fight against people who challenge him is similar to the roosters. The roosters underscore the difficulty of life for Kino, because he is poor and has little control over his own life.
The ants are powerless, just as Kino is.
The ants were busy on the ground, big black ones with shiny bodies, and little dusty quick ants. Kino watched with the detachment of God while a dusty ant frantically tried to escape the sand trap an ant lion had dug for him. (ch 1)
Kino may have God-like control over the ants, but he has little control over his own life. The powerful men, such as those that review his pearl, play with him just as he plays with the ants.