Sometime in the past, the birds had a language that everyone understood.
One day, the birds decided that they should have a king. So all the birds gathered including one small one that didn’t have a name. They decided that whoever could fly the highest would be the king. So they all took off and soon the eagle was way above everyone else.
Everyone was about to proclaim the eagle king when the small unnamed bird – who had been hiding in the eagle’s feathers – took off and flew higher. “I am king!” he cried.
The other birds didn’t care for this trickery so they decided that whoever could get lowest on the ground would be king. The other birds tried to dig themselves down, but the little nonamed bird found a mouse hole and slipped inside, crying, “I am king!”
The other birds didn’t care for this, so they set the owl to watch the mouse hole while they all went to bed. Eventually, the owl fell asleep and the little bird was able to escape. Since then the owl has stayed away from daylight because the other birds are still angry with the owl. And sometimes the little bird still calls out “I am king!” while he hides in the hedgerows.
I’m guessing the willow-wren makes a cry that sounds like, “I am king!” and thus this little tale to explain it. Also why owls stay out at night and like to hunt mice.
I guess this tale is a bit odd since the hero is usually the one that outwits his fellows. But I guess that doesn’t work all the time.