Running into the Lion's Den: Naïve 3-day-old Domestic Chicks Are Attracted to Predator Voices

Voice perception plays a critical role in assessing the presence of other animate beings in the surrounding environment. However, despite the ubiquitous presence of this acoustic phenomenon, the fundamental characteristics that constitute the core of voice-likeness remain unclear. Promising candidates could include the harmonic structure of vocalizations, the specific timbre, or a complex combination of various features. In the present study, naï ve 3-day-old domestic chicks (Gallus gallus) were tested using a running wheel paradigm to investigate whether they exhibit an indiscriminate attraction to voice-like stimuli, regardless of the species producing those sounds, thus proving the existence of an innate predisposition that could constitute the acoustic parallel of the visual preference for biological movement. To achieve this, the animal subjects were exposed to four different stimuli, consisting of vocalisations emitted by as many tetrapod species, both predators – American alligator (Alligator mississippiensis) and dog (Canis lupus familiaris) - and non-predators – common toad (Bufo bufo) and mallard (Anas platyrhynchos). Intriguingly, preliminary results revealed a significant increase in motor activity in domestic chicks in response to the calls of predators. However, no significant pattern in approach response was observed for the vocalizations of nonpredator species, even when closely related, such as the mallard. These findings, although initially puzzling, suggest the potential existence of an innate auditory predisposition in domestic chicks, prompting them to respond to specific aspects of voice-likeness associated with emotional and motor arousal, aspects that may be perceived by chicks as being more pronounced in predator voices.