Explanation

Peacock, Pigeon, and Parrot:

Names are gender-neutral (can refer to males or females of the species).

• Peacock = Male/Female (though commonly used for males, the species is "peafowl").
• Pigeon = No distinct gender in the name.
• Parrot = No distinct gender in the name.

Peahen:

• Specifically refers to the female of the peafowl species.
• The male is called a peacock, making "peahen" gender-specific.