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Emerging pathogens: fungal host jumps following anthropogenic introduction omit an important additional dimension. In birds, sexual dimorphism in singing and song learning varies greatly among species, and sex differences in brain morphology are the most extreme documented in any vertebrate [2, 3]. Differences in female song-learning strategies might be even greater than those observed in male vocal learning, ranging from no learning to learning as much as males do [3, 4]. Similar to males, individual females also vary in song complexity [5] and sharing levels [6, 7]. In reviewing the functional basis of different songlearning strategies, the authors group Repertoire hypotheses, which suggest learning is advantageous where female preferences select for larger repertoires, and Sharing hypotheses, which suggest that learning songs shared with neighbours leads to selective advantage. Neither hypothesis …