The bird cannot learn a dialect. Vocal output cannot be matched to the unimproved template. Summary of development of bird song. Marler's experiments clearly show the interaction between innate and environmental factors. Sparrows have dialects.
Isolated birds show deficiencies in their song but it does contain elements of adult song.
Marler believes this is because bird is born with a template of what their species song sounds like. Isolated birds can only produce this crude template song. The song of a deafened bird is even cruder. Normal birds adjust their song to what it hears from adults in the vicinity. Here is an experiment which shows that learning can take place by simply practising a response without any reinforcement.