Yawning in sync: implications for social cohesion in horses

Yawning in sync: implications for social cohesion in horses
Curr Zool. 2024 Sep 16;71(2):137-151. doi: 10.1093/cz/zoae052. eCollection 2025 Apr.
Authors
Alice Galotti 1 , Martina Romano 2 , Paolo Baragli 3 4 , Elisabetta Palagi 1 5
Affiliations

1 Unit of Ethology, Department of Biology, University of Pisa, via Alessandro Volta 6, 56126, Pisa, Italy.
2 Department of Biology, University of Florence, Via Madonna del Piano 6, Sesto Fiorentino, Firenze, Italy.
3 Department of Veterinary Sciences, University of Pisa, Viale delle Piagge 2, 56124, Pisa, Italy.
4 Bioengineering and Robotic Research Centre “E. Piaggio,” University of Pisa, Largo Lucio Lazzarino 1, 56122, Pisa, Italy.
5 Natural History Museum, University of Pisa, Via Roma 79, 56011, Calci, Pisa, Italy.

PMID: 40264711
PMCID: PMC12011488
DOI: 10.1093/cz/zoae052

Abstract

The increasing interest in the study of spontaneous (SY) and contagious yawning (CY) was so far focused on several taxa, especially primates. Here, we focused on SY and CY in horses, a suitable species due to their complex social dynamics that has been largely overlooked in research on these phenomena. By analyzing videos of 48 horses on pasture, we identified 2 yawning morphologies: Covered (YCT) and Uncovered Teeth (YUCT). Using EquiFACS, we quantitatively demonstrated that YCT and YUCT differ in terms of muscle recruitment. Moreover, we provide the first evidence for the presence of CY by comparing 2 different conditions: chewing-yawn-chewing versus chewing-chewing-chewing. Supporting the Social Modulation hypothesis, in our mares, CY was more prominent among subjects sharing good relationships. Moreover, subjects responded more rapidly to kin compared with non-kin and kin frequently grooming each other responded even more rapidly to each other yawns. The high familiar yawn sensitivity can provide selective advantages increasing behavioral synchronization and group cohesion.

Keywords: EquiFACS; Equus caballus; Yawn contagion; social modulation hypothesis; yawn morphologies.

© The Author(s) 2024. Published by Oxford University Press on behalf of Editorial Office, Current Zoology.