Citation: Krueger, K.; Trager, L.; Farmer, K.; Byrne, R. Tool Use in Horses. Animals 2022, 12, 1876. https://doi.org/10.3390/ani12151876 Academic Editor: Michael Peterson Received: 9 June 2022 Accepted: 20 July 2022 Published: 22 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). animals Article Tool Use in Horses Konstanze Krueger 1,2, * , Laureen Trager 2,3 , Kate Farmer 4 and Richard Byrne 4 1 Department Zoology/Evolutionary Biology, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany 2 Department Equine Economics, Faculty Agriculture, Economics and Management, Nuertingen-Geislingen University, Neckarsteige 6-10, 72622 Nürtingen, Germany; laureen.esch@gmx.de 3 Department of Animal Welfare, Ethology, Animal Hygiene and Animal Husbandry, Veterinarian Medicine, Ludwig Maximilian University Munich, Veterinärstr. 13/R, 80539 München, Germany 4 Centre for Social Learning & Cognitive Evolution, School of Psychology, University of St Andrews, St Andrews KY16 9JP, Scotland, UK; katefarmer74@gmail.com (K.F.); rwb@st-andrews.ac.uk (R.B.) * Correspondence: konstanze.krueger@hfwu.de Simple Summary: Tool use has not yet been confirmed in horses, mules or donkeys. As this subject is difficult to research with conventional methods, we used crowdsourcing to gather data. We asked equid owners and carers to report and video examples of “unusual” behaviour via a dedicated website, and we searched YouTube and Facebook for videos of equids showing tools. From 635 reports, including 1014 actions, we found 13 unambiguous cases of tool use. Tool use was associated with restricted management conditions in 12 of the 13 cases, and 8 of the 13 cases involved other equids or humans. The most frequent tool use, with seven examples, was for foraging, for example, equids using sticks to scrape hay into reach. There were four cases of tool use for social purposes, such as horses using brushes to groom others, just one case of tool use for escape, in which a horse threw a halter when it wished to be turned out, and one case of tool use for comfort, in which a horse scratched his abdomen with a stick. Equids therefore can develop tool use, especially when management conditions are restricted, but it is rare. Abstract: Tool use has not yet been confirmed in horses, mules or donkeys. As this subject is difficult to research with conventional methods, we used a crowdsourcing approach to gather data. We contacted equid owners and carers and asked them to report and video examples of “unusual” behaviour via a dedicated website. We also searched YouTube and Facebook for videos of equids showing tool use. From 635 reports, including 1014 behaviours, we found 20 cases of tool use, 13 of which were unambiguous in that it was clear that the behaviour was not trained, caused by reduced welfare, incidental or accidental. We then assessed (a) the effect of management conditions on tool use and (b) whether the animals used tools alone, or socially, involving other equids or humans. We found that management restrictions were associated with corresponding tool use in 12 of the 13 cases (p = 0.01), e.g., equids using sticks to scrape hay within reach when feed was restricted. Furthermore, 8 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. There was 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. Keywords: crowdsourcing; horse; innovation; mule; management; tool use 1. Introduction Tool use has been described in a wide range of animal species [1], meeting the defini- tion “ ... the external employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user Animals 2022, 12, 1876. https://doi.org/10.3390/ani12151876 https://www.mdpi.com/journal/animals