| Abstrakt: |
Lyrebird vocal display consists of mimicry of natural sounds interspersed with territorial song and other specific signals. Mimicked sounds are culturally transmitted by adult males and not learned by young birds from the models, but further sounds may subsequently be added to or deleted from the repertoire. There was no evidence of mimicry of man-made sounds. Albert's Lyrebird Menura alberti mimicry has a repeating sequential pattern that is quieter than the loud territorial song and has developed into an extended song directed at nearby females. A loud signal within the song alerts distant females. Superb Lyrebird M. novaehollandiae mimicry has no specific order and is as loud as the territorial song but is more subdued in the presence of the female prior to copulation. It acts as a non-threatening directional beacon to keep the lines of communication open. The territorial songs of both species are wholly learned and vary regionally more in the Superb Lyrebird than in Albert's Lyrebird. Analysis of the prolonged and complex nature of these displays in a dispersed lek situation suggests early steps in the evolution of passerine song. Winter breeding and freedom from parental duties provide males with a vast vocabulary of mimicked sounds and the opportunity to develop vocal learning that has produced a prolonged statement containing diverse and clear messages, whereas spring-breeding male passerines have been forced into compressed coded messages that are harder to interpret. |
