King of the Birds

An ancient fable (known to Aristotle) tells how the birds wanted to elect a king, and it was decided that it should be the bird that flew highest. An eagle outflew all the other birds, but was beaten by a wren that had hidden in his plumage.

A website called The White Goddess says that the wren's status as king of the birds is reflected in the name given to it in many European languages: Latin (regulus), French (reytelet), Welsh (dryw), Teutonic (Koning Vogel), Dutch (Konije, 'little king'). Some of these seem to be slightly inaccurate, but the principle seems to be sound.

There is a Celtic tradition of hunting wrens at Christmas time, and parading them through the streets, or round the houses asking for gifts of food, money or alcoholic drinks in exchange for a look at the captured bird. There are several well–known folk songs related to this custom, one of the best–known being The King, which was recorded by Steeleye Span and released on the 1971 album Please to See the King. The album title refers to the same custom. A website that rejoices in the name of Proto–Indo–European Religion has a detailed account of these customs.

Note however that Wikipedia also says that in heraldry, the eagle is known as the king of birds (in contrast to the lion, which is the king of beasts).

Interesting that the question setter chose the wording "King of All Birds". If you google this, the first page of hits is dominated by a song by the Irish–American singer and songwriter Aoife (pronounced eefuh, apparently) O'Donovan. It seems to be her biggest hit. It's not really about birds, but it uses birds as an extended metaphor for the singer's character and disposition. It includes the line "I'm a little wren / I'm happiest when I'm on the wing of a friend".