Investigating determinants of yawning in the domestic (Equus caballus) and Przewalski (Equus ferus przewalskii) horses

Abstract

Yawning is rare in herbivores which therefore may be an interesting group to disentangle the potential function(s) of yawning behaviour. Horses provide the opportunity to compare not only animals living in different conditions but also wild versus domestic species. Here, we tested three hypotheses by observing both domestic and Przewalski horses living in semi-natural conditions: (i) that domestic horses may show an elevated rate of yawning as a result of the domestication process (or as a result of life conditions), (ii) that individuals experiencing a higher level of social stress would yawn more than individuals with lower social stress and (iii) that males would yawn more often than females. The study involved 19 Przewalski horses (PHs) and 16 domestic horses (DHs) of different breeds living in large outdoor enclosures. The results showed that there was no difference between the PH and DH in yawning frequency (YF). PHs exhibited much higher levels of social interactions than DHs. There was a positive correlation between yawning frequency and aggressive behaviours in PHs, especially males, supporting the idea that yawning may be associated with more excitatory/stressful social situations. A correlation was found between yawning frequency and affiliative behaviours in DHs, which supports the potential relationship between yawning and social context. Finally, the entire males, but not castrated males, showed much higher levels of yawning than females in both species. The intensity (rather than the valence) of the interaction may be important in triggering yawning, which could therefore be a displacement activity that helps reduce tension.

Horse Preferences for Insolation, Shade or Mist Curtain in the Paddock under Heat Conditions: Cardiac and Behavioural Response Analysis

“…Yawning occurred mainly in IS and was rarer in MC, whereas it did not appear in SH. Studies on the yawning frequency proved several factors eliciting this behaviour connected with, among others, excitatory or stressful social situations [ 27 ], frustration and stereotypic behaviour [ 33 ], alertness or drowsiness state [ 34 ], as well as thermoregulation and brain cooling [ 35 , 36 ]. The higher rate of yawning in IS in the current study could have been mainly caused by the drowsiness state of the horses, thermoregulation, and brain cooling, since the horses were turned out in solitary and no stressful situations occurred.…”

“…These behaviours were considered exclusively in terms of time, i.e., in the percentage of time spent in the experimentally different paddock areas (IS, SH, or MC). Moreover, two non-locomotor behaviours were taken into account: rate of vocalisations [ 26 ] and yawning [ 27 ] per min of staying in these areas. The types of calls were not distinguished since their prevalence was low.…”

Assessing equine emotional state

“…Yawning behaviour could also convey information regarding mental state as it is generally considered to be triggered by stress and emotional contexts (Fureix et al, 2011;Górecka-Bruzda et al, 2016), but findings to date are inconclusive.…”

Not all yawns tell the same story: The case of Tonkean macaques

“…Such variability may be associated with different social contexts (Vick & Paukner, 2010 ). Therefore, yawning is considered as a behavioral pattern that can have different functions in different circumstances (Baenninger, 1997 ; Górecka‐Bruzda et al, 2016 ; Guggisberg et al, 2010 ; Leone et al, 2014 ; Zannella et al, 2015 , 2017 ).…”

“…yawning is considered as a behavioral pattern that can have different functions in different circumstances (Baenninger, 1997;Górecka-Bruzda et al, 2016;Guggisberg et al, 2010;Leone et al, 2014;Zannella et al, 2015Zannella et al, , 2017.…”