A study published in Annals of the New York Academy of Sciences has unexpectedly found that rhythmic passive movements, such as rocking or carrying-like motions, can change the emotional state of domestic chicks, inducing both calming and pleasurable responses. The study, conducted by Cinzia Chiandetti, Andrea Dissegna and Paolo Gallina from the University of Trieste, and Lorenzo Scalera from the University of Udine, investigates the effects of rhythmic motion in animals outside the mammalian class.

In mammals, slow rhythmic passive motion has long been recognized as an important component of parental care: it can reduce crying, lower heart rate and promote sleep. In humans, anecdotal observations also suggest that faster rhythmic movements in babies and young children, such as playful tossing in the air, swinging or rides such as roller coasters, can elicit pleasure and excitement.

To test whether these effects also occur outside mammals, and to understand when motion shifts from a primarily calming function to a potentially pleasurable one, the research team observed domestic chicks while they were being rocked. The use of chicks to study this phenomenon is unprecedented: these animals are able to walk immediately after hatching and, unlike mammalian infants, are not carried by their mother.

During the experiment, individual chicks were placed inside an opaque box attached to a precision robotic arm, programmed to reproduce rocking and carrying-like motions while varying their frequency — slow or fast — and direction — horizontal or vertical. The animals’ emotional state was monitored non-invasively by recording their vocalizations.

The results show that slow rocking and slow carrying-like movements reduce so-called “contact calls”, vocalizations associated with discomfort, isolation or separation. This finding mirrors the calming effects of maternal carrying already documented in mammals.

A particularly significant result, however, concerns the possibility that specific forms of rhythmic movement can also induce a positive response. When the chicks were exposed to fast horizontal rocking or fast carrying-like movements, they emitted a significantly higher number of affiliative vocalizations — so-called brood calls — which are usually produced in safe and socially positive contexts and are considered indicators of a pleasurable state.

Taken together, the findings suggest that the calming effects of carrying and rocking observed in mammals may stem from a widespread sensitivity to rhythm and motion in animals.

As the study’s authors note: “Our findings expand the functional scope of rhythmic stimulation, positioning it as a regulator of affect with both calming and pleasurable dimensions across vertebrate lineages.”

Because chicks do not experience maternal carrying in their natural history, their sensitivity to rhythmic movement appears to reflect a deeply conserved mechanism across vertebrates, rather than a response to specific parental care strategies.

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