What is the origin of the idiom "pigeon pair" and when to use it?

The idiom "pigeon pair" originated in the early 20th century and was derived from the pigeon's tendency to lay two eggs at a time, typically one male and one female. This idiom is used to describe the gender composition of siblings in a family. It indicates that the family has one child of each gender. It is often used colloquially to describe the birth of a boy and a girl in quick succession.