Tool Use in Horses

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.

Full text

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
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animals
Article
Tool Use in Horses
Konstanze Krueger 1, 2, * , Laureen Trager 2,3, Kate Farmer 4and Richard Byrne 4
1Department Zoology/Evolutionary Biology, University of Regensburg, Universitätsstraße 31,
93053 Regensburg, Germany
2Department Equine Economics, Faculty Agriculture, Economics and Management,
Nuertingen-Geislingen University, Neckarsteige 6-10, 72622 Nürtingen, Germany; laureen.esch@gmx.de
3Department of Animal Welfare, Ethology, Animal Hygiene and Animal Husbandry, Veterinarian Medicine,
Ludwig Maximilian University Munich, Veterinärstr. 13/R, 80539 München, Germany
4Centre 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

Animals 2022,12, 1876 2 of 10
itself when the user holds or carries the tool during or just prior to use and is responsible
for the proper and effective orientation of the tool”. In horses, mules and donkeys, tool use
has not yet been demonstrated, even though it may be considered likely [
2
] as equids are
mostly kept under human management and tool use has been reported more frequently in
captive animals [3,4].
That horses may have the ability to use tools is suggested by evidence of their innova-
tive abilities. Equids developed innovative solutions for handling complicated feeders [
5
]
and for dealing with environmental restrictions in foraging, movement and social con-
tact [
6
–
10
], for example, by opening locked doors and gates and by harvesting apples by
kicking the trees [
2
,
11
]. Others developed “less immediately functional” innovations for
play and comfort, such as playing with sticks and piling up soft bedding for resting and
sleeping [
2
]. Some of the innovations were solitary and served the innovator itself, but
others were social and were directed towards conspecifics and humans [
2
]. The observation
of innovative social behaviour is in line with prior demonstrations of horses using symbols
for heterospecific communication, that is to say, communication with another species, when
requesting humans to put on or take off a rug [
12
], or for prompting people to open gates
to allow access to feed [13,14].
The lack of reports of tool use in equids may simply reflect the phenomenon’s rar-
ity [
3
,
4
]. Evidence for the existence of such rare behaviour may be obtained from crowd-
sourcing [
15
]. For example, previous crowdsourcing studies have analysed the range of
flexibility of animal problem-solving abilities [
16
], cognitive capacities in goats [
17
], door
opening techniques, and innovative behaviour in horses [
2
,
11
]. Several methods have
been used. Some amassed reports retrospectively, submitted by specialist researchers or
enthusiasts, including studies on birds [
18
,
19
], primates [
20
–
22
], elephants [
15
], dogs [
23
],
horses [
11
,
24
] and general wildlife [
25
]. Efforts need to be made to exclude reports that do
not meet the definitions [19,26].
Others have searched journals for keywords such as “unusual” or “novel” [
18
,
19
,
22
,
27
].
A third approach is to ask trained personnel and researchers for contemporary reports [
15
].
A fourth has been to search internet platforms such as YouTube or Facebook for video
material of animal behaviour, as applied in a study on human responses to tail chasing in
dogs [
28
], play in dogs and horses [
26
], and door opening and innovations in horses [
2
,
11
].
If videos with unclear or manipulated content are excluded, and layperson documentations
are available that clearly demonstrate that films have not undergone any postproduction
editing, YouTube and Facebook videos can provide very useful raw footage [26,29].
Data collection of this kind runs the risk of compiling false or unrepresentative reports,
thereby generating a biased data set [
19
,
30
,
31
]. In addition, responses may be biased by
the over-representation of reports from highly motivated respondents [
32
], reports about
socially desirable items (such as a “clever animal”) or even the respondents’ moods [
30
].
However, the approach has advantages that may offset its deficiencies. It potentially
provides a large data set of rare observations [
3
,
4
], which could not possibly be collected
by a single research team engaged in experimentation [
4
,
15
,
18
,
25
,
26
,
29
,
33
]. A large sample
size increases the credibility of reports [
15
] especially when data such as pictures or videos
are available [29,33,34].
In our study, we contacted equid owners and caretakers directly and via the internet
and asked them to observe and document unusual behaviour by video and questionnaire
at the website (https://innovative-behaviour.org accessed on 10 July 2022). In addition, we
searched the internet platforms YouTube and Facebook for videos of equids showing tool
use [
2
,
11
]. Among 635 reports, which collectively described or depicted 1014 behaviours,
we found 13 cases that were in line with the definition of tool use [1].
In addition to discovering whether equids used tools [
1
,
35
], we also hoped to clarify
the conditions which promote the development of tool use. We asked (a) whether certain
management situations favour the development of tool use in equids [
2
] and whether
(b) individual
equids use tools solitarily, socially in an interspecific context with other
equids, or in a heterospecific context with humans [12–14].

Animals 2022,12, 1876 3 of 10
2. Materials and Methods
2.1. Study Location, Website, and Videos
Horse, mule, and donkey owners and caretakers were asked to report on “unusual”,
novel behaviour through a website (https://innovative-behaviour.org accessed on 10 July
2022), via horse journals, Facebook, various private websites, and at conferences and public
talks in Germany, Austria, France, Hungary, Switzerland, the UK, and the U.S.A., between
July 2012 and December 2021. Reports were submitted in English, German, or French. We
used a quantitative–qualitative mixed questionnaire approach as described in detail by [
2
],
Krueger et al. (2021 a). In addition, we collected unusual behaviours, and environmental
and individual specific aspects, shown on video material from the internet platforms
YouTube and Facebook with the keywords “clever”, “smart”, “unusual”, “play”, “open
door”, “open gate”, “escape”, “run away”, “horse”, “pony”, “donkey”, and “mule”. The
complete resulting data set is available in previous publications on door and gate opening
behaviour [11] and on innovative behaviour in equids [2].
2.2. Cases and Case Selection
Tool use (e.g., Figure 1) was reported for 20 equids (Table S1), mostly as a side
observation of 635 reports, which collectively described or depicted 1014 innovative
behaviours [11].
Animals 2022, 12, x FOR PEER REVIEW 3 of 10
In addition to discovering whether equids used tools [1,35], we also hoped to clarify
the conditions which promote the development of tool use. We asked (a) whether certain
management situations favour the development of tool use in equids [2] and whether (b)
individual equids use tools solitarily, socially in an interspecific context with other equids,
or in a heterospecific context with humans [12–14].
2. Materials and Methods
2.1. Study Location, Website, and Videos
Horse, mule, and donkey owners and caretakers were asked to report on “unusual”,
novel behaviour through a website (https://innovative-behaviour.org accessed on 10 July
2022), via horse journals, Facebook, various private websites, and at conferences and pub-
lic talks in Germany, Austria, France, Hungary, Switzerland, the UK, and the U.S.A., be-
tween July 2012 and December 2021. Reports were submitted in English, German, or
French. We used a quantitative–qualitative mixed questionnaire approach as described in
detail by [2], Krueger et al. (2021 a). In addition, we collected unusual behaviours, and
environmental and individual specific aspects, shown on video material from the internet
platforms YouTube and Facebook with the keywords “clever”, “smart”, “unusual”,
“play”, “open door”, “open gate”, “escape”, “run away”, “horse”, “pony”, “donkey”, and
“mule”. The complete resulting data set is available in previous publications on door and
gate opening behaviour [11] and on innovative behaviour in equids [2].
2.2. Cases and Case Selection
Tool use (e.g., Figure 1) was reported for 20 equids (Table S1), mostly as a side obser-
vation of 635 reports, which collectively described or depicted 1014 innovative behaviours
[11].
Figure 1. Horse using a stick to scrape hay into reach (Video S1).
Figure 1. Horse using a stick to scrape hay into reach (Video S1).
Contentious cases were excluded from the total data set as described in [
2
]. The
20 “tool use”
cases were rated by three independent observers, one professor, one PhD
student and one bachelor’s student in equine science, on whether they were unambiguous.
The observers agreed in 100% of the cases (inter-observer agreement: Cohen’s Kappa
κ
= 1)
and found 13 cases to be unambiguous (Figure 1; Tales 1and S1; Videos S1–S6) and seven
ambiguous (Table S1; Video S7). The seven ambiguous cases were excluded from further

Animals 2022,12, 1876 4 of 10
analysis because they may have reported actions that were not innovative tool use. They
may have been:
(a)
About trained behaviour (n= 1): one video clearly showed that the behaviour was
aided and reinforced verbally and with feed (Video S7).
(b)
Possibly the result of reduced welfare (n= 1), but not a solution for the underlying
deficiency [
9
,
10
]: for example, one horse showing repetitive, stereotypic behaviour
when scraping the ground with a stick (Table S1).
(c) Did not fit the definition [
1
] used in the study (n= 5), because the manipulated objects
were not detached from the environment (Table S1).
Table 1.
Tool use in equids categorized according to its direction: interspecific = directed towards
other equids (brown), heterospecific = directed towards humans (green), solitary = for the tool using
animal itself (blue).
Type Description Sex Restricted
Access to
Behaviour
Category
Interspecific
(involving equids)
Heterospecific
(involving people)
Solitary
Mare (M)
Gelding (G) Stallion (S)
Pasture (P) Equids (E)
Roughage (R)
Social
Forage
Escape
Comfort
Interspecific
Horse A uses large stick to chase horse B
and make B move faster. G Unrestricted Social
Interspecific
Video S2
Horse A takes bucket in its mouth and
swings it at horse B, who is eating from a
full bucket. A continues until B retreats
and A can eat from the full bucket.
Unknown Unknown Forage
Interspecific Horse picks up brushes and tries to
groom other horses. G R Social
Interspecific
Video S3
Mare and foal in a box, foal grooms
mother with comb. Unknown Unknown Social
Heterospecific Horse picks up a stick and swings it at
person. G R Social
Heterospecific
Horse bangs bucket against wall to
demand feed, When on a low fenced
paddock, he throws the bucket over the
fence towards the feed room.
S Unrestricted Forage
Heterospecific
At feed time, horse throws the empty
feed bucket in front of the owner. When
she fills the bucket, the horse drags it into
his stable.
G E Forage
Heterospecific
Video S4
Horse grabs the halter next to the box
and throws it at the owner’s feet.
Behaviour developed when was on box
rest and so had restricted movement,
forage and social contact.
G P + E Escape
Solitary
Video S5
Horse picks up stick and scratches
abdomen/belly with it. G unrestricted Comfort
Solitary
Horse uses a stick to rake hay out from
the hay rack when hay is almost empty.
Other horses observe and eat from the
raked hay.
G R Forage
Solitary
Video S6
Horse takes a stick in its mouth and uses
it to rake hay from under the hay rack.
Horse brings stick in from outside the
stable for this.
G R Forage
Solitary
Video S6
Mule takes a stick in his mouth and rakes
hay from underneath the hay rack, after
observing a horse doing the same and
eating the raked hay. Mule started raking
hay when the horse was removed from
the group.
G (Mule) R Forage
Solitary
Video S1
The horse takes a stick in her mouth and
rakes hay within reach. She eats the hay,
then searches for the stick again, and
repeats behaviour.
M P + R Forage

Animals 2022,12, 1876 5 of 10
The remaining 13 cases (Table 1; Figure 1; Videos S1–S6) were chosen for investigation.
Nine owners reported that they did not encourage the equids to show the behaviour, two
gave food as part of regular feeding routines after the behaviour was shown and in two
cases the reaction of the persons was unknown.
2.3. Animals
The animals were 13 domestic equids, comprising 1 mule and 12 horses. They com-
prised one female, nine castrated males, one uncastrated male, and two equids for which
the sex could not be discerned. The mean age at which equids were reported to have started
showing the behaviour was 6.5 years (median, min. = 0.5, max. = 14). The horses were
of various breeds and these were summarised according to the breed types deployed in
genetic studies [
36
,
37
]: thoroughbred horses (n= 1), Arabian horses (n= 3), and warmblood
horses (n= 6). In two cases the breed type was not reported or was not obviously visible
in the videos. Animal characteristics which were not reported or clearly visible in videos
were not considered for the analysis (Table S1).
From the case descriptions and the videos, we identified the housing and management
conditions: nine equids were kept in group stabling and three in single box stabling (one
unknown), nine had unrestricted access to pasture and two restricted access to pasture
(two unknown), nine had unrestricted contact to other equids and two restricted social
contact (two unknown), five received unrestricted roughage and six restricted roughage
(two unknown).
2.4. Behavioural Categories
Tool use cases were assigned to four behavioural categories developed from the
immediate, observable context in which the behaviour was shown. We classified the
categories as escape (n= 1), foraging (Figure 1;n= 7), comfort (n= 1) and social (n= 4) [
2
]
(Table 1).
Seven equids showed their respective tool use more than 20 times, four showed it 2–10
times, and in two cases the frequency of the behaviour was unknown. Apart from tool
use, some equids showed a median of 1 (min. = 0, max. = 4) further behaviours that were
classified as “innovative“ [2] (Table S1).
From the case reports or the videos, we concluded whether the tool use was solitary
(was only for use of the tool using animal itself and did not include any other individual;
Figure 1) or was interspecific (included another equid) or heterospecific (included a person;
Table 1).
2.5. Data Analysis
R Studio (version 0.99.484, Boston, MA, USA) [
38
] of the R-Project statistical environ-
ment (R Development Core Team, 2022) and the Rcommander (package Rcmdr) were used
for statistical analysis and the depiction of the data. Most of the data were not normally
distributed (Shapiro–Wilk test). Likelihood equations were calculated with chi-squared
tests for ordinal data and with binomial tests for binomial data (File S1). A Spearman
rank correlation test was applied to compare the variance of management data and tool
use behaviour categories (File S1). The significance level was set at 0.05 and all tests
were two-sided.
3. Results
Among the equids reported displaying “unusual behaviour” only 13 out of 1014
showed unambiguous tool use. Equids showing tool use were mostly castrated males
(chi-squared test: n= 11,
χ
= 11.636, df = 2, p= 0.003), rather than females (binomial test:
n= 10, p= 0.02) or uncastrated males (binomial test: n= 10, p= 0.02; File S1).
Restrictions in the equids’ management conditions correlated with the behavioural
category under which we recorded the tool use: horses with restrictions in free movement
showed tool use for escape, equids with restrictions in access to feed primarily displayed

Animals 2022,12, 1876 6 of 10
tool use for foraging (Figure 1), and horses with restrictions in social contact displayed
social tool use (Spearman correlation test: n= 13, rs = 0.708, p= 0.01; Table S1; File S1). The
only case which we categorized as tool use for comfort was displayed by a horse that lived
under conditions which covered all basic needs.
Tool use reported for enhancing comfort (n= 1) was solitary. Tool use for foraging
(
n= 7
) was solitary in most cases (Figure 1;n= 4), but in one case included a mule, and
in two cases humans. Tool use which served social purposes (n= 4) was interspecific
(
n= 3
), i.e., included other horses, or heterospecific (n= 1), i.e., included humans. The only
escape tool use reported (n= 1) was heterospecific, the tool used to enhance free movement
included a person (Figure 2).
Animals 2022, 12, x FOR PEER REVIEW 6 of 10
and tool use behaviour categories (File S1). The significance level was set at 0.05 and all
tests were two-sided.
3. Results
Among the equids reported displaying “unusual behaviour” only 13 out of 1014
showed unambiguous tool use. Equids showing tool use were mostly castrated males (chi-
squared test: n = 11, χ = 11.636, df = 2, p = 0.003), rather than females (binomial test: n = 10,
p = 0.02) or uncastrated males (binomial test: n = 10, p = 0.02; File S1).
Restrictions in the equids’ management conditions correlated with the behavioural
category under which we recorded the tool use: horses with restrictions in free movement
showed tool use for escape, equids with restrictions in access to feed primarily displayed
tool use for foraging (Figure 1), and horses with restrictions in social contact displayed
social tool use (Spearman correlation test: n = 13, rs = 0.708, p = 0.01; Table S1; File S1). The
only case which we categorized as tool use for comfort was displayed by a horse that lived
under conditions which covered all basic needs.
Tool use reported for enhancing comfort (n = 1) was solitary. Tool use for foraging (n
= 7) was solitary in most cases (Figure 1; n = 4), but in one case included a mule, and in
two cases humans. Tool use which served social purposes (n = 4) was interspecific (n = 3),
i.e., included other horses, or heterospecific (n = 1), i.e., included humans. The only escape
tool use reported (n = 1) was heterospecific, the tool used to enhance free movement
included a person (Figure 2).
Figure 2. Tool use context and direction in horses. Blue colouration indicates that tool use was
solitary (n = 5), green colouration that tool use included a conspecific (n = 5), and brown colouration
that it included humans (n = 3).
4. Discussion
Crowdsourced reports and videos provided 13 descriptions of tool use [1,35], in 12
horses and 1 mule. To our knowledge, this is the first time that tool use in equids has been
Figure 2.
Tool use context and direction in horses. Blue colouration indicates that tool use was solitary
(n= 5), green colouration that tool use included a conspecific (n= 5), and brown colouration that it
included humans (n= 3).
4. Discussion
Crowdsourced reports and videos provided 13 descriptions of tool use [
1
,
35
], in
12 horses
and 1 mule. To our knowledge, this is the first time that tool use in equids has
been scientifically described and supports the suggestion that rare instances of tool use in
other “non-tool using species” may be found in the future [3,4].
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 [
10
]. Others may have used tools to
enrich their social situation [
10
]. Some tool use for feeding, and all tool use in social
situations, included other equids (was interspecific) or humans (was heterospecific). Tool
use that included other individuals may have served to communicate insufficiencies in
basic needs [
10
], comparable to findings in equids that displayed referential heterospecific
communication [
12
–
14
], when asking humans to take off or put on a rug, or when asking
for access to feed.

Animals 2022,12, 1876 7 of 10
Communicating needs by using tools requires a more complex mental level, compared
to direct actions such as pointing with the head at desired feed [
13
,
14
]. When a horse
indicates a wish by directing the attention of a person towards a desired feed item by body
movements, it demonstrates an understanding of the direction of the person’s attention [
39
]
and in the person understanding the pointing behaviour [
14
]. In addition, when a horse
appears to communicate a need to be led out of the stable by throwing a halter, which
is used for leading, or a need for feed by throwing an empty feed bucket, in front of an
approaching person, the horse displays an understanding of communal belief [
40
], i.e., the
communal understanding that a halter needs to be put on to leave the stable and a bucket
needs to be filled for feeding.
However, tool use in equids may not primarily be prompted by resource shortage, as
was concluded for innovative behaviour in a feeding and escape context [
2
,
24
]. Favourable
living conditions, in which all the needs of the equids are covered [
10
], may also encourage
the development of tool use, as shown for most innovations in comfort and play situa-
tions [
2
]. Play may also prompt the development of tool use [
41
]. This is supported by
the finding that more males than females used tools in the present study and male horses
have been reported to play more than females [
42
,
43
]. 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 [
2
]. 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.
Potential Biases in the Data
It is important to acknowledge potential biases in our data. Collecting data with
crowdsourcing methods may introduce biases into the data set. We took care to ex-
clude unreliable or biased reports [
19
,
26
], one possibly on reinforced (i.e., trained) be-
haviour and one on reduced welfare [
9
,
10
,
25
], and supported the reports with pictures and
videos [
2
,
22
,
28
,
29
,
33
]. This allowed data to be amassed with some replications of very rare
observations [
30
] and allowed a cautious approach to the analysis of the circumstances of
tool use [15,18,25,26,29,33].
In all behaviour categories, present and previous owners may have unintentionally
reinforced the behaviour by rewarding the animal with enhanced affection [
31
]. Therefore,
the present study applied two direct and two catch questions [
24
] to filter reports of
unintentionally trained behaviour by present owners. The catch questions asked whether
the equids received feed in the immediate context of showing the behaviour or whether
the present owners were pleased when they observed the behaviour and may, therefore,
have provided unintentional reinforcement in the form of increased attention or positive
reactions, of which the horse previously learned to be followed by rewards. However,
unintentional reinforcement of present owners or training by previous owners might not
have been obvious in all cases.
In addition, it is important to acknowledge the limitations of crowdsourcing methods,
as they may affect the interpretations. Where we find that a factor covaries with tool
use frequency, that could be a genuine finding or an artefact generated by bias in the
respondent’s behaviour or reporting. For instance, the lack of observations of tool use
in the context of escape may be a genuine finding. It may also reflect a biased tendency
of respondents to keep equids in pleasant management conditions where animals do not
escape. Furthermore, bias may arise because respondents were pleased to detect and report
tool use for foraging, comfort and social communication more enthusiastically [
31
], relative
to equid owners keeping their horses in conditions that prompted their escape. In addition,
equids may apply tool use for escape mostly when they are unobserved. Owners intervene

Animals 2022,12, 1876 8 of 10
to prevent escape if they see it happening, because it may result in serious accidents [
44
,
45
],
and horses may be punished for trying to escape. Therefore, learning to use a tool to
help them escape may be something horses do when no one is around. Access to data on
management conditions amongst all equid owners would have been ideal. This would
allow statistical analyses to quantify the level of bias. While that was not possible for the
current study, it may remain a possibility for future studies.
It is unknown whether such biases exist, and, if so, their magnitude. Therefore, we take
our findings at face value and provide interpretations that would be appropriate for an unbi-
ased 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.
5. Conclusions
We conclude that horses have the potential to develop behaviour involving tool use,
particularly to improve their situation when management conditions are restricted, for ex-
ample for foraging and improving social contact; however, this remains a rare phenomenon.
Supplementary Materials:
The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/ani12151876/s1, Table S1: data tool use in equids; File S1: statistical
data; Video S1: horse rakes hay; Video S2: YouTube, horse chases other horse; Video S3: YouTube,
foal grooms mother; Video S4: horse throws halter; Video S5: horse uses stick to scratch abdomen;
Video S6: horse and mule rake hay; Video S7: YouTube, unintentionally trained horse uses rope.
Author Contributions:
Conceptualization, K.K. and R.B.; methodology, K.K. and R.B.; validation,
K.K.; formal analysis, K.K. and L.T.; investigation, K.K. and L.T.; resources, K.K.; data curation,
K.K. and K.F.; writing—original draft preparation, K.K., L.T., K.F. and R.B.; writing—review and
editing, K.K., L.T., K.F. and R.B.; visualization, K.K.; supervision, R.B.; project administration, K.K.
and L.T.; funding acquisition, K.K. All authors have read and agreed to the published version
of the manuscript.
Funding:
The article processing charge was funded by the Baden-Wuerttemberg Ministry of Science,
Research and Culture and the Nuertingen-Geislingen University in the funding program Open
Access Publishing.
Institutional Review Board Statement:
This study is registered under the No. 2021_29_14.05.2022
at Nuertingen-Geislingen University. No animal tests were conducted for the study, no human
data is given in the study, and all procedures performed in the study involving animal and human
participants were approved by the institutional research committee at Nuertingen-Geislingen Uni-
versity and fulfilled the Data Protection Directive of the European Union (DSGVO 2016) and the
1964 Helsinki declaration and its later amendments or comparable ethical standards. The video
material and replies to questionnaires were transferred into anonymous, written form directly after
receiving the material. Only the written, anonymous raw data were used for further analysis in
the study. The study published no pictures, videos or any data from which personal data could be
drawn, either in the manuscript or in any Supplementary Materials. We obtained written informed
consent from all persons who answered the questionnaire and send videos. On the website or via
email, all responders agreed to the anonymous publication of their written data and videos for
scientific purposes. Reasonable requests for access to anonymous agreements can be obtained from
the corresponding author. Some videos were published on YouTube with a Creative Commons CC BY
licence (https://support.google.com/youtube/answer/2797468?hl=en&ref_topic=2778546 accessed
on 10 July 2022). They are available and can be used without any restriction. Other videos were
published with the standard YouTube or Facebook license. These can be looked at and links can be
forwarded without any restriction, which was the default setting for all uploads (see YouTube and
Facebook Terms of Service: https://www.youtube.com/t/terms accessed on 10 July 2022, Facebook
https://www.facebook.com/legal/terms accessed on 10 July 2022). Links for Videos from YouTube
and Facebook are shown in Supplementary Data (Table S1).
Informed Consent Statement:
Informed consent was obtained from all subjects involved
in the study.
Data Availability Statement:
Thedata presented in this studyare available in the
Supplementary Materials.

Animals 2022,12, 1876 9 of 10
Acknowledgments:
We wish to thank Kevin Laland for discussion, Michel-Antoine Leblanc and
Anja Zollinger for helping with the French survey, Knut Krueger for setting up and managing the
website, two student project groups, Simone Weil, and Helena Hollenhorst for helping to raise the
data, various journalists for spreading information about the project and all the horse, donkey and
mule owners and keepers for sending us their reports.
Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or
in the decision to publish the results.
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