What is the origin of the idiom "eat like a bird" and when to use it?

The idiom "eat like a bird" originated from the misconception that birds eat very small quantities of food, given their size. This phrase is often used to describe individuals who have very small appetites or who consume minimal portions of food during meals. In reality, many birds eat a significant amount of food relative to their body weight, but the idiom has persisted in popular language to describe people who eat sparingly.