Final answer:
Female birds choosing mates based on traits like singing ability or physical appearance is part of the evolutionary process called sexual selection, specifically through intersexual selection, where females choose males with desirable traits leading to reproductive success and potential sexual dimorphism.
Step-by-step explanation:
When a female bird chooses a mate based on characteristics such as singing ability or physical appearance, her discrimination is part of the evolutionary process known as sexual selection. Sexual selection operates through two main mechanisms: intrasexual selection, which is competition among members of the same sex, often males, for access to mates; and intersexual selection, which involves mate choice, where individuals of one sex (usually females) select mates based on certain desirable traits.
Intersexual selection occurs when females choose a male based on specific traits that are indicative of the male's fitness. For instance, male bowerbirds build elaborate structures called bowers and decorate them to attract female counterparts. These traits, although sometimes appearing maladaptive for survival, persist because they provide a reproductive advantage to those who possess them.
Overall, sexual selection leads to increased reproductive success of individuals who exhibit preferred traits, resulting in the potential development of sexual dimorphism within species, where the two sexes display distinct physical characteristics unrelated to reproductive organs.