Birdsong performance studies: reports of their death have been greatly exaggerated

Kroodsma (2017, Animal Behaviour, 125, e1-e16) has critiqued 'the performance hypothesis', which posits that two song attributes, trill rate and frequency bandwidth, provide reliable indicators of singer quality and are used as such in mate or rival assessment. Kroodsma develops three main arguments: (1) young male sparrows copy songs with high accuracy from neighbours, and thus cannot calibrate song models to their own performance capacities; (2) in species with song repertoires, vocal performance varies widely within individuals and among song types, thus rendering song performances inadequate as quality indicators; and (3) experimental studies of song function have relied on playback of structurally abnormal stimuli, with interpretation of birds' responses to these stimuli thus compromised. I address these critiques in turn, offering the following counterpoints: (1) the reviewed literature actually reveals substantial plasticity in song learning, leaving room for birds to tailor songs to their own performance capacities; (2) reasonable scenarios, largely untested, remain to explain how songs of repertoire species could convey information about singer quality; and (3) the playback studies critiqued actually enable direct, reasonable inferences about the function of vocal performance variations, because they directly contrast birds' responses to low- versus high-performance stimuli. My analyses support the plausibility of performance hypotheses and highlight avenues for future research. My analyses also reveal numerous shortcomings with Kroodsma's arguments, including an inaccurate portrayal throughout of publications under review, logic that is thus rendered questionable and reliance on original data sets that are incomplete and thus inconclusive.