Physiological resonance between mates through calls as possible evidence of empathic processes in songbirds
Résumé
Physiological resonance –where the physiological state of a subject generates the same state in a perceiver – hasbeen proposed as a proximate mechanism facilitating pro-social behaviours. While mainly described in mammals,state matching in physiology and behaviour could be a phylogenetically shared trait among social vertebrates.Birds show complex social lives and cognitive abilities, and their monogamous pair-bond is a highlycoordinated partnership, therefore we hypothesised that birds express state matching between mates. Weshow that calls of male zebra finches Taeniopygia guttata produced during corticosterone treatment (after oraladministration of exogenous corticosterone and during visual separation from the partner) provoke both an increasein corticosterone concentrations and behavioural changes in their female partner compared to controlcalls (regular calls emitted by the same male during visual separation from the partner only), whereas calls producedduring corticosterone treatment by unfamiliar males have no such effect. Irrespective of the caller status(mate/non-mate), calls' acoustic properties were predictive of female corticosterone concentration after playback,but the identity of mate calls was necessary to fully explain female responses. Female responses were unlikelydue to a failure of the call-based mate recognition system: in a discrimination task, females perceive callsproduced during corticosterone treatment as being more similar to the control calls of the samemale than to controlcalls of other males, even after taking acoustical differences into account. These results constitute the first evidenceof physiological resonance solely on acoustic cues in birds, and support the presence of empathicprocesses.