Baby wrens have to chirp a tune to be fed
Baby wrens must produce a tune to be fed that they have previously learned from their mothers. A study, published in the journal Current Biology, says the bird's learning this code is the way to indicate to their mothers to feed them.
This was found when the mothers were producing these tunes and voicing them to their unhatched eggs. When they further looked into this, they found that each mother produced a different tune to their eggs. This then lead to understanding that this call was in the call from the babies to the mothers when receiving food. To confirm that this prediction was correct, the researchers interferred the babies call to the mother and therefore stopped the feeding process.