between model song and mimicked song. For example, one study found that strike-thrushes did not respond any differently to hearing their own songs than to hearing imitations by lyrebirds. Generally, juveniles initially learn mimetic items through transmission by older lyrebirds, rather than from the model species themselves. This is reflected in the vocalisations of lyrebirds in the Sherbrooke Forest in Victoria, which were observed to frequently mimic the song of pilotbirds, a species that had not been recorded in the area for over 10 years. During the winter when the nestlings hatch, adults more frequently mimic model species that are less active during this time, again suggesting that mimetic items are initially learnt from other lyrebirds. The quality of mimetic song increases with age, with adult superb lyrebirds having both greater accuracy and a more diverse repertoire of mimetic songs when compared to subadult birds. Subadult lyrebirds produce recognisable imitations, which fall short of adult versions in terms of frequency range, consistency and acoustic purity, for example in imitations of the complex whipbird call. Like many passerine species, there are significant differences in lyrebird song in different populations over its geographic range. These include differences in repertoire and vocalisation characteristics, and may be due to differences in local bird species assemblages, which provide different options for model selection. It could also be due to differences in the acoustic environment mediated by vegetation structure, with lyrebirds more likely to mimic fragments of bird songs that are most acoustically prominent. Mimicry as a sexually selected trait The mimicry of male superb lyrebirds is a well-known example of a sexually selected trait. Females prefer males that produce more accurate mimicry and that have a greater diversity of mimetic songs in their repertoire. Although to the human ear the differences between songs are indistinguishable, there are differences in the mimetic song quality between individual lyrebirds due to signal degradation, reverberation and attenuation, as well as the frequency and volume attained. There is evidence that there are costs associated with the development of mimetic song, and while these costs are currently unknown, they indicate that that quality of a lyrebird's mimetic song is an honest signal that can be used by females in mate selection. Mimicry in females Historically, there has been far more research on the mimetic abilities of male lyrebirds. This is primarily due to the assumption that the evolution of song in