Ontogenic shift in the usage and function of a symbolic bird gesture

Abstract

Gestures are an integral part of human communication, and the characterisation of pointing (deictic) and meaningful (symbolic) gestures in non-human primates helps retracing the origins of our own communication system. A recent discovery in Japanese tits (Parus minor) suggested that individuals use a symbolic wing-fluttering gesture to prompt the mating partner to enter the nest first. Symbolic gestures are thus likely more ancestral than previously thought, but the presence of this gesture in related species, the degree to which it is tied to feeding context and whether gestural usage changes across development remain unexplored. To fill these gaps, we studied the wing-fluttering gesture in great tits (Parus major), observing both fledglings and adults in various contexts around nests and away from nests in their natural environment. Our findings showed that wing-fluttering was primarily used by females near nests, almost exclusively in the presence of their mate, and stopped when the mate entered the nest. As in Japanese tits, our results suggest that wing fluttering serves as a symbolic gesture prompting the mate to enter the nest more quickly to feed the nestlings. In contrast, fledglings used wing-fluttering to prompt their parents to feed them and stopped gesturing after having been fed. Our study further indicates deep evolutionary roots of symbolic communication and highlights how functional shifts in gestural usage can operate across development to match age-specific needs.