Later in the season, birds are busy feeding their young and levels of testosterone drop dramatically and are replaced by a 'lutinizing' hormone, which stimulates parenting behavior and a reduction in song. For others the same song serves both functions. Females may use the vigor of a song to judge a potential mates qualities. Female birds of a number of different species have been shown to settle based on the males' dawn chorus performance. Poldmaa says, one theory suggests males are announcing to each other that they have survived the night and are still ready to defend their territory.
Spring nights are cold, predators abound, and it is the most dangerous of times.
Most birds that die do so during the night, so the morning is when territory vacancies will be most noticeable. If their neighbour isn't' on his favorite perch at the crack of dawn there is a good chance he didn't survive the night and his absence is a signal to other males this 'territory is vacant and available' and the signal to the females that her mate is dead. If he did survive the night but fails to muster up a good vocal performance it can send the message to other males that he is too weak to defend his territory or his mate, Poldmaa says. In fact, Poldmaa says, much of the scientific work done on the transmission of human dialects has come from the study of birds. It has been found birds of a particular species in one area will sound slightly different in another.