Maybe puberty? Sherlock
The Birds can only learn whistles and hoots. They learn them by attempting to mock voice pitch.
Observational learning
Learn songs
Yes, most can. Getting to learn birds songs make it easier to tell what kind of bird it is. (Example... Some birds have long loud songs and others, short soft songs... some even the other way around.)
No
Inheritance influences the development of birdsongs as the basic song for all birds of the same species is the same. If a bird is raised in isolation it can still sing but its song will lack complexity. Learning also plays a role as young birds learn details of songs from their fathers or other birds. This ability to learn is genetic.
Birds do not sing for pleasure, they sing to communicate with other birds. There are territorial songs intended to warn off competitors, and mating songs intended to attract mates.
To support the idea that language is culturally transmitted, researchers used evidence of the studies of birds when they begin to produce songs. They concluded that id birds are kept isolated from hearing birds their speech will be abnormal versus a bird hearing songs other birds called.
All birds can learn to varying degrees. Some can talk, some whistle or mimic other sounds. Some only sing their normal song. Birds learn their songs from their parents and others in their flock. A captive bird will imitate you or other sounds they hear repeatedly.
One of the songs that Walt Disney listened to and liked was called Feed the Birds. The song was from the Mary Poppins.
The English translation for Weihnachtslieder is Christmas carols. Two types are distinguished, the songs which have a Christian background are called 'Adventlieder' (songs of the advent period) whereas songs with more generic themes such as snow are called 'Winterlieder' (songs of winter).
The easiest songs for children to learn and sing are happy and catchy songs. Songs dealing with Christmas are ones that children learn fast and sing. 'Rudolph the Red Nosed Reindeer' and 'Jingle Bells' was popular Christmas songs.