Answer:
Sexual Dimorphism.
Step-by-step explanation:
When males or females of one species face a lot of competition to reproduce with individuals of the opposite sex, it is likely that a trait called sexual dimorphism will evolve in this species, that is, males and females will have distinct morphological traits from each other. This is because in a highly competitive reproductive environment there is a greater chance that traits attractive to the opposite sex will be more often selected. A classic example of sexual dimorphism in birds is the peacock's ornate tail, which gives males reproductive advantage (males with larger and more ornate tails are preferred by females).