Good defensive formations are the cornerstone of any winning team, and the same goes for horse herds, fresh research suggests.
Researchers in Poland monitored the responses of pastured horses to predator calls. They found two distinct breed-dependent defensive formations were employed, but cannot fully explain what they represent.
Iwona Janczarek and her colleagues said animal social strategies are important when avoiding predators.
They hypothesized that horses, despite domestication stretching back to antiquity, would still react to the calls of predators, and demonstrate anti-predator behaviour.
For their study, they played recorded vocalisations of three different predators — the howl of the grey wolf, the roar of the Arabian leopard and the barking howls of the golden jackal — to two herds comprising 10 Polish Konik horses and 10 Arabian horses.
The jackal, a smaller opportunitistic feeder, was chosen as the control sound.
The horse herds were exposed to the vocalisations of one of the predators in each of six trials conducted nine days apart.
In each trial, the selected predator was played for five minutes.
The reactions of the horses were monitored and recorded.
“The results of our study confirmed that predator vocal cues alone triggered instantaneous changes in the grazing behaviour of horses, provoking alertness, engagement in higher gaits and grouping,” the researchers said.
“Their social responses and tactics in anti-predator behaviour differed between the breeds and between predators,” they reported in the open-access journal Animals.
The Koniks, on hearing a howling wolf, formed tight groupings, while Arabians exposed to the growling of a leopard responded with a linear group formation.
“The type of spatial formation (a bunch versus a line) of the herd in response to the perceived presence of a predator appears to be linked to the breed, which is an important outcome.
“This demonstrates the probable strategy the equine herd employs during a potential risk of predation.”
The strong relationship between the breed and predator area of origin was also a highly notable outcome, the researchers said.
Not all behaviours were displayed equally by Koniks and Arabians.
“Contrary to the expectation that the Arabians were more prone to alertness, they indeed stood still for longer periods than the Koniks when exposed to the vocalisations of jackals and wolves.
The Koniks were more alert in response to the wolf howls, while the Arabians were more responsive to the leopard growls.
The Koniks formed a cohesive group to seemingly avoid the purported predator, while the Arabians actively approached the loudspeakers in a line.
“The circular herd formation found in Koniks may be a better strategy than a linear formation to avoid wolf predation.
“It may be hypothesized that the bunching may be a better strategy in response to group-hunting predators, while linear formation may be more effective in the case of a solitary hunting predator, but this is highly speculative.”
Proximity to other herd members in the case of a predator attack has many benefits, including a reduced risk of being caught.
“The observed linear group formation in the Arabians could be only incidental; however, a variety of defensive formations in ungulates has been previously observed.
“For instance, elephants and bison have all been observed to form defensive circles. Sheep and cows adopt different herd formations depending on their activities, such as grazing, resting, ruminating or in response to the presence of a predator.”
The study team acknowledged that the response of horses could be different if they were not enclosed in a restricted area.
“However, the observed behaviour was reported also by breeders of Hutzul horses, who eye-witnessed the spatial organisation in free-pastured herds in reaction to wolves.”
Despite unlimited space for fleeing, the Hutzul mares bunched, keeping their foals inside the herd formation.
“Such behaviour might explain higher efficiency in foal protection by bunched herds, as during the chase the foals could be easier target s for wolves.”
Janczarek and her colleagues said their results suggest that keeping horses in groups may help horse breeders diminish the risk of predation in areas with wolves.
“Our study,” they said, “is the first to confirm that synchronized reactions and decreased distancing between individuals occur in this species as a social anti-predatory behaviour.
“But more extensive studies are needed to explore horse-predators interaction.”
They continued: “Due to unavailable scientific evidence of how wolves hunt horses, more field studies on horse-predator interactions are urgently needed.”
They suggest it is likely that horses are able to assess the size of a predator based on vocal cues.
Adult horses were able to respond to potential predation as a group, expressed by alertness and defensive formations.
This, they said, indicates existence of the social anti-predator behavior, which in turn may explain the low rates of horses falling prey to predators as compared with other farm animal species.
The study team comprised Janczarek, Anna Wiśniewska and Ewelina Tkaczyk, all with the University of Life Sciences in Lublin; Michael Chruszczewski, with the University of Warsaw; and Aleksandra Górecka-Bruzda, with the Polish Academy of Life Sciences.
Janczarek, I.; Wiśniewska, A.; Chruszczewski, M.H.; Tkaczyk, E.; Górecka-Bruzda, A. Social Behaviour of Horses in Response to Vocalisations of Predators. Animals 2020, 10, 2331.