Tool use by horses confirmed in just-published study

A horse uses a stick to scrape hay into reach.
A horse uses a stick to scrape hay into reach. Source: Krueger et al.

Tool use by horses has been confirmed by researchers in a just-published study, although they say it is rare.

German zoologist and behaviour researcher Konstanze Krueger and her colleagues, reporting in the journal Animals, said they identified 13 unambiguous cases of tool use. Twelve involved horses and one involved a mule.

The study team used a crowdsourcing approach to gather data because of the difficulties in researching the subject with conventional methods.

Tool use has been described in a range of animal species, the study team noted.

Until now, they said, tool use has not yet been shown in horses, mules and donkeys, even though it may be considered likely as equids are mostly kept under human management and tool use has been reported more frequently in captive animals.

“That horses may have the ability to use tools is suggested by evidence of their innovative abilities.”

Equids, they noted, have developed innovative solutions for handling complicated feeders and dealing with environmental restrictions in foraging, movement and social contact – for example, by opening locked doors and gates and by harvesting apples by kicking the trees.

The 13 examples of tool use classified as unambiguous. Those in brown were directed toward other equids; those in green are directe towards human; and those in blue were solitary use. Source: Krueger et al.
The 13 examples of tool use classified as unambiguous. Those in brown were directed toward other equids; those in green are directed towards humans; and those in blue were solitary use. Source: Krueger et al.

Others have developed less functional innovations for play and comfort, such as playing with sticks and piling up soft bedding for resting and sleeping.

“The lack of reports of tool use in equids may simply reflect the phenomenon’s rarity,” they said.

For their study, the researchers asked online for horse, mule, and donkey owners and caretakers to report on “unusual” novel behaviour. They also made appeals at conferences and during public talks in Germany, Austria, France, Hungary, Switzerland, Britain and the United States. Reports were submitted in English, German, or French.

The study team also searched YouTube and Facebook for material.

In all, 635 reports collectively described or depicted 1014 behaviours. Tool use was reported for 20 equids, mostly as side observations among the 635 reports.

The 20 instances were rated by three independent observers – one professor, one doctoral student and one bachelor’s student in equine science – in an effort to rule out any contentious cases. To be classed as unambiguous, it had to be clear that the behaviour was not trained, caused by reduced welfare, or that it was incidental or accidental.

In the end, 13 examples were considered unambigious, with the three observers in 100% agreement. The examples involved one mare, nine geldings, one stallion, and two equids for which the sex could not be discerned.

The seven ambiguous cases were excluded from further analysis. The study team examined the effect of management conditions on tool use and whether the animals used tools alone, or socially, involving other equids or humans.

The authors found a link between management restrictions and tool use in 12 of the 13 cases. For example, equids used sticks to scrape hay within reach when feed was restricted. Eight of the 13 cases involved other equids or humans, such as horses using brushes to groom others.

The most frequent tool use was for foraging, with seven examples. Tool use for social purposes was seen in four cases, and there was just one case of tool use for escape.

The study team found just one case of tool use for comfort, and in this instance, there were no management restrictions.

“Equids therefore can develop tool use, especially when management conditions are restricted, but it is a rare occurrence,” they concluded.

The researchers said they believed it was the first time that tool use in equids has been scientifically described. Their findings, they said, support the suggestion that rare instances of tool use in other “non-tool using species” may be found in the future.

“Equids may develop tool use for various reasons, the most common being to improve their situation when management conditions are restricted.

“Some displayed solitary tool use and may have done so to enhance the fulfilment of their own needs, such as free movement, comfort and their feeding conditions. Others may have used tools to enrich their social situation.”

While tool use in the current study was often linked to management restrictions, favourable living conditions may also encourage the development of tool use, they said, as shown for most innovations in comfort and play situations.

“The small sample size of tool use to improve comfort in the present study does not allow for robust conclusions on the reason for tool use development in equids and so remains mostly descriptive.

“Interestingly, in contrast to the single case of tool use for escape in the present study, escape, rather than foraging, social purposes or comfort was reported to be the main context for equids to develop generally innovative solutions.

“Furthermore, equids may display oral tool use in most cases because it is difficult to perform delicate manipulations with hoofs, and this may result in tool use for foraging more often than for other purposes, as in the present study.”

The authors said it was important to acknowledge potential biases in the data. “Collecting data with crowdsourcing methods may introduce biases into the data set. We took care to exclude unreliable or biased reports.”

However, unintentional reinforcement by the present owners or training by previous owners might not have been obvious in all cases.

It is unknown, they said, whether certain biases exist in crowdsourced data, and, if so, their magnitude. “Therefore, we take our findings at face value and provide interpretations that would be appropriate for an unbiased data set.

“However, we stress that until such a time as the level of bias can be quantified, our findings should be regarded as provisional and suggestive rather than definitive.”

The study team comprised Krueger, with the University of Regensburg and Nuertingen-Geislingen University, both in Germany; Laureen Trager, with Nuertingen-Geislingen University and Ludwig Maximilian University Munich; and Kate Farmer and Richard Byrne, with the University of St Andrews in Scotland.

Krueger, K.; Trager, L.; Farmer, K.; Byrne, R. Tool Use in Horses. Animals 2022, 12, 1876.

The study, published under a Creative Commons License, can be read here

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