Birds or bird related characteristics have been used in many idioms. If taken literally, they just wouldn't make any sense. Here is a fun collection along with their interpretations....

"A little bird told me." - Something that you say in order to let someone know that you are not going to tell them who gave you the information being discussed.

"A bird in the hand is worth two in the bush." - Having something that is certain is much better than taking a risk for more, because chances are you might lose everything.

"As free as a bird."  Completely free to do what you want and without any worries.

"As light as a feather." - weighs very little.

"As the crow flies." - travel distance by the shortest and most direct route

"As wise as an owl" - someone who is very wise

"Birdbrain" - a person with confused ideas; incapable of serious thought

"Bird's eye view" - panoramic view; a situation or topic as if viewed from an altitude or distance

"Birds of a Feather flock together"  - something that you say which means people who have similar characters or similar interests will often choose to spend time together

"Eagle eye" - acute eyesight; an intently watchful eye

"Eat like a bird" - to eat very little

"For the birds" - objectionable or worthless

"Give someone the bird" - refers to giving the finger to someone

"In fine feather" - in excellent form, health, or humor

"Kill two birds with one stone" - to manage to do two things at the same time instead of just one

"Rare bird" - a rare or unique personannoyed or irritated

"Rule the roost" - to be the person who makes the decisions

"Spread Your Wings" - to start to do new and exciting things for the first time in your life

"Take Someone under your wing" - to help, protect or mentor someone

"The early bird gets the worm" - something that you say in order to tell someone that if they want to be successful they should do something immediately

"Try out one's wings" - to try to do something that you have recently learned to do

"Winging it" - to say or do something without preparation, forethought, or sufficient information or experience; improvise