Effective Rewards

Behaviour that is reinforced is likely to be repeated. This is how horses are trained. There are two kinds of reinforcers, primary reinforcers and secondary reinforcers.

Primary reinforcers are valuable to the horse of themselves. Secondary reinforcers are rewarding only when they are consistently paired with a primary reinforcer. Let’s look at some examples.

Primary Reinforcers	Secondary Reinforcers
Release of pressure	The ‘Click’ in clicker training
Food	Vocal rewards (good boy)

Another commonly used method of reinforcing behaviour is petting or scratching the horse, often near the withers. This has been reported to lower the horse’s heart rate, and many horses appear to enjoy the scratch, closing their eyes, wiggling their lips, and extending their necks.

Is tactile reinforcement primary or secondary?

A 2010 study using 20 horses trained them to stand still at a vocal command for increasing duration up to a minute. Half were rewarded for correct responses with food and half were rewarded with vigorous wither scratching. The researchers tested the horses’ relationship to humans before and after the training, examining latency to approach a stationary person and how long the horse stayed close to them. They also looked at the horses’ ability to perform the learned behaviour after the training was over.

Interestingly, they found that the wither scratch group did not learn as well as the food reward group. They were unable to stand still for as long, and did not learn as fast. The food reward group also approached a stationary human faster after training and stayed closer for longer than the tactile reward group, though both groups had started out scoring the same for approach latency and time in proximity on the relationship tests.

The researchers suggested that tactile rewards may have been given too much credit, and that carefully used food rewards are more efficient in terms of both horse learning and relationship building.

Some horses really enjoy touch, but all of them seem to enjoy food! Learning how to use food well in training seems like a logical choice from the results of this study.

The study, The Way to a Man’s Heart is Through His Stomach: What About Horses? by Sankey, C; Henry, S; Górecka-Bruzda, A; Richard-Yris, M-A; and Hausberger, M was published by PLoS ONE in November 2010, Volume 5, Issue 11, and can be found for free online here: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0015446

Research, Solving Behaviour Problems, Training Traditions

Trust? Or Safety?

Safety is very important to horses. While the most common horse training methods employ food or the release of pressure as a reward, it has recently been argued that safety is valuable enough to horses to be used by trainers as a resource during training to reduce fearfulness and increase learning uptake.

The goal of horse training is to reduce the expression of behaviour we don’t want and to draw out behaviour we do want, so that it is eventually offered on cue. Many behaviours that horses offer that we don’t like stem from fear. When a behaviour originating from fear is punished to make it less likely to occur again, negative emotions are likely to result, reducing effectiveness of training. Therefore, it is critical to understand fear responses in order to make better training decisions.

Fear responses are highly selected for because they promote survival. Fear is a kind of stress, and affects the animal’s behaviour in ways designed to make it easier to escape the situation. When fear is excessive or chronic, however, the physical cost of responding to the fear can affect health and behaviour. Animals may also react fearfully to things that do not pose an actual risk.

When a horse successfully escapes a fear-inducing stimulus (be that a plastic bag, a bush, or a rider), the behaviour that succeeded can be learned in a single trial, has the effect of reducing fear caused by the stimulus, and is resistant to being untrained. This suggests that the reduction in fear associated with performing an escape behaviour is highly reinforcing. Escape behaviour is in contrast to avoidance behaviour, where the animal receives warning about a fear-inducing stimulus and has the opportunity to avoid the stimulus by performing a behaviour.

In laboratory avoidance learning tests, when a ‘safety signal’ or neutral stimulus such as a light or a sound occurred when the animal had successfully avoided the fear-inducing stimulus, the test animals learned the avoidance behaviour much faster. The safety signal by itself reduced fear and held positive reinforcing properties. Once a stimulus becomes a safety signal, it rarely loses its meaning!

Other horses are probably the most common example of equine safety signals. Calm horses have the best effect, and silhouettes of relaxed or grazing horses have been shown to be recognized and greeted by horses. ‘Home’ is also likely to be a safety signal.

Reducing fearfulness should be a goal of horse training. It is possible that humans could also become a safety signal, depending on the horse’s previous experience of its handler specifically and people in general. The safety signal concept could be a better definition of the elusive notion of ‘trust’ in horse-human relationships.

If the horse’s trainer, handler, or owner can be perceived by the horse as a source of safety through consistent and careful training, learning could be enhanced and the risk of injury to horse and handler caused by a fear response could be greatly reduced.

McGreevy, P; Henshall, C; Starling, M; McLean, A; Boakes, R. (2014) The Importance of Safety Signals in Animal Handling and Training. Journal of Veterinary Behaviour, 9:382-387.

Research

Teaching a Horse to Choose

A recent article looking for ways to improve research into the preferences of horses found that horses can be taught to communicate preferences to their handlers by using symbols. Mejdell et al (2016) used positive reinforcement training to teach 23 horses to choose whether or not to wear a blanket, and tested the efficacy of the training through weather challenges. They predicted that if the horses had correctly learned to discriminate the symbols they would vary their choices based on the weather.

Horses were trained over 14 days to understand the consequences of choosing the ‘blanket on’ symbol versus the ‘blanket off’ symbol both in their home box and outdoors. At first the horse was taught to touch a single board with their nose and were rewarded for this. Then the relevant symbol was shown to the horse (i.e. ‘blanket on’ symbol if no blanket was worn at the time of the training), the horse was rewarded for touching it, and the action was carried out. ‘Blanket on’ and ‘blanket off’ symbols were then presented together, and only the relevant choice was rewarded until no mistakes were made.

Finally a ‘no change’ symbol was added with the other relevant symbol. This was the beginning of introducing choice to the horse. Either choice was rewarded and carried out accordingly. A choice of ‘no change’ prompted the trainers to perform a sham handling of the horse as if putting on a blanket or taking one off to prevent horses from choosing ‘no change’ simply to avoid being touched. Random choices were then presented, with only the relevant choices being rewarded, and irrelevant ones being ignored until no mistakes were made. When horses passed this stage, they moved on to temperature challenge tests to ensure they understood the consequences of choosing different symbols.

For the temperature challenge, horses were rugged heavily indoors until they were obviously warm, then presented with the choices of ‘no change’ or ‘blanket off’ until they reliably chose the obvious answer (but all choices were still rewarded). The cold challenge was outdoors until mild signs of temperature discomfort were shown, then the ‘no change’ or ‘blanket on’ choices were given. After passing this stage, the horses were ready for preference testing.

On two warm, pleasant days and two cold, unpleasant days, the horses were taken from their paddock to the test area in a random state of blanketed or not blanketed. The symbols were varied in position and relative distance to each other. The horses’ responses were very consistent with the weather; all horses chose ‘blanket off’ on the warmer days when wearing one, or ‘no change’ when not. On the cold days, all but two horses chose ‘no change’ when wearing one or ‘blanket on’ when not.

The researchers concluded this kind of training is an effective way to study preferences in horses, and can be used in the field in place of less portable Y-maze testing that has been done previously to determine preference.

The article is open access and can be found with this reference:

Mejdell, C; Buvik, T; Jørgensen, G; Bøe, K. (2016) Horses can learn to use symbols to communicate their preferences. Applied Animal Behaviour Science, 184 pp 66-73. https://doi.org/10.1016/j.applanim.2016.07.014

Research

What does your horse want?

Horses have preferences, which they appear motivated to communicate with us when given the opportunity. Some horses enjoy firm brushing while others prefer limited grooming, and handlers well-versed in their body language can often determine what a horse is enjoying or wanting more of but it is often difficult to tell for sure. Researchers recently trained horses to use symbols to communicate their preferences about being blanketed or not in a much less ambiguous way!

It took all 23 horses used in the trial less than 14 training days to grasp the concept of bumping one symbol with their nose to have their blanket removed, another to have a blanket put on, and a third to remain as they were. This rapid uptake speaks well of the chosen positive reinforcement conditioning scheme the researchers used, and perhaps also of the horses’ motivation to make a choice for their own thermal comfort.

The researchers reported that once the horses began to understand that they could communicate their wishes, many horses even attempted to get the trainer’s attention from the paddock on a testing day and immediately chose blanket off. On removing it, it was found that the horse had become sweaty under the blanket, making the reason for the choice obvious.

On warm days, with temperatures around 20ºC, horses consistently chose to have their blanket removed if they wore one, or chose no change if they did not. On days where the weather was cold (~9ºC), wet, and/or windy, all but two of the horses chose blanket on if they did not have one, or no change if they did. This indicates that horses’ preferences are individual, with some horses having a higher tolerance for cold temperatures than others, with blanketing preferences to match. This was expected by the researchers, and confirms what we see in our horses every day.

For the owner looking for a challenging training project, teaching your horse to discriminate between symbols related to his management could take some guesswork out of the many choices we have to make for our horses. But for those owners who may not have the expertise yet to accomplish this, simply paying attention to your horse’s behaviour during routine handling can give insight into his preferences. Encouraging this communication by honouring it will help your horse to express himself more freely, building your relationship and mutual understanding!

The article is open access and can be found with this reference:

Research

Talking to your Horse

Horse people talk to their horses. We praise them, cajole them, complain to them, tell them our cares and worries, and sometimes even shout at them. Many of us believe our tone of voice, if not our words, affect our horses’ behaviour. Heleski et al conducted a study in 2015 to find out to what extent soothing voice cues versus harsh ones affect training.

How the Study was Conducted

Their hypothesis was that a soothing cue as the horse progressed through a potentially frightening task would improve the speed with which the horse was able to complete it calmly, while a harsh cue provided as the horse progressed would slow down the learning process and increase arousal.

Over 100 horses from different stables through Europe and the United States had five trials to cross a tarpaulin spread on the ground. The horses were randomly assigned to harsh voice treatment (quit it!) and soothing voice treatment (good horse). The handler led the horse towards the tarp using pressure and release on the halter, adding the appropriate vocal cue for each correct step towards the tarp. If the first crossing attempt took longer than ten minutes, the horse was considered to have failed. The goal was for horses to cross calmly within five trials. The time taken to cross each time, the horse’s heart rate, and its general behaviour were observed and recorded.

Results

Interestingly, their findings were exactly opposite to their hypotheses. There was no significant difference between harsh voice and soothing voice treatment groups in the percentage of horses that failed the learning task, in the groups’ average heart rates, or in the total time each group required to cross calmly. The maximum heart rate of the soothing voice group was actually higher than that of the harsh voice group.

There were no significant correlations with the horses’ ages when taken as an average. However, when 3-4 year old horses were compared with those 20 years or more, the older ones had much less latency to cross.

In the end, the harsh voice treatment group actually completed the learning task faster than the soothing voice group. The researchers hypothesized that these unexpected results may show that tone of voice is either not distinguishable to the horse, or is not as salient to the horse as pressure cues, and may have ended up being perceived as ‘background noise’. They also suggested that handlers who were more familiar to the horses might have produced different results.

Conclusion

This shows that while a soothing voice is likely not inherently calming to a horse in a novel situation, yelling at a horse for unwanted behaviour is equally ineffective. It is, however, theoretically possible with classical conditioning to teach a horse the difference between soothing voice and harsh voice. A soothing voice may additionally help the handler to remain calm, and correlations between horse and handler heart rates have been previously shown.

So, keep talking to your horse. Just realize that he is not taking in everything you are saying, and how you are saying it. Instead, make sure your training is clear so you get the responses you want.

Reference

Heleski, C; Wickens, C; Minero, M; Dalla Costa, E; Wu, C; Czeszak, E; and Köenig von Borstel, U. (2015) Do soothing vocal cues enhance horses’ ability to learn a frightening task? Journal of Veterinary Behaviour, 10(1):41-47.

Research, Training Traditions

Speaking Horse—How Body Language Affects Training

What is Body Language?

Body language is common in animals and is a way of showing intention. It is unconsciously created by thoughts of performing an action, which results in tiny muscle contractions that show a shadow of the intent. Humans can consciously affect their body language, but it is unlikely that animals are capable of this kind of deception.

Many natural horsemanship trainers read their horse’s body language with precision and react swiftly to what they see, effectively employing reinforcement in a timely manner to train the horse. The best trainers have impeccable timing and know their subject’s language as well as their own.

The Natural Explanation

How natural horsemen explain this phenomenon, however, becomes confusing. Are they talking back to the horse in the same language to achieve the training result? But they don’t have long ears or a tail, which horses use extensively in communication, and while posture could be used, cocking a hind leg just doesn’t look the same with our two-legged stance. Does the horse see such a trainer as a higher herd member and obey because of their communication techniques? Then no novice rider would be able to have control over their horse, because they are clueless about body language at first. What is really going on here?

The Research Explanation

When humans read horse body language and interpret it correctly, their safety improves as they are able to avoid dangerous situations, and their training improves as they reward or correct behaviours appropriately as soon as they are shown. These interactions follow the principles of equitation science and employ addition (positive) and subtraction (negative) reinforcement rather than showing characteristics of a conversation.

Horses also quickly learn what our body signals mean, typically through classical conditioning. They learn that one action (such as shifting the gaze) precedes another (such as being driven away from the trainer) and begin responding to the gaze to avoid the driving. Increased heart rate in a rider results in increased heart rate in their mount, probably for similar reasons.

However, the number of human to horse interactions with body language that directly matches horse to horse interactions are very few indeed, if an ethogram (a list of all the possible behaviours of a species) is examined.

Conclusion

What does this mean for training? It is extremely important for trainers to understand horse body language. This provides valuable information about the horse’s intent, even though it is doubtful that horses see humans as herd members, interpreting their body language as that of a horse. Instead of trying to communicate to the horse in ‘horse’, then, we should focus on helping them understand what our body language means by being consistent, timing our reinforcement well, and using the principles of equitation science.

Bibliography

Ladewig, Jan. (2019) Body Language: Its Importance for Communication with Horses. Journal of Veterinary Behaviour: 29, 108-110.

Ladewig, Jan. (2007) Clever Hans is still whinnying with us. Behavioural Processes: 76, 20-21.

Research

Out in the Cold

Introduction

As the weather gets colder and we start to put on layers and stay inside, it is easy to assume that our horses would prefer to be inside a heated building, in the comfort of a deep bedded stall. Sometimes we keep horses inside for our own convenience—they can’t get dirty, don’t take as long to catch, or can cool down before being put outside—but sometimes it is done from the honest conviction that the horse would prefer it that way.

Many people know about the evidence to the contrary, that horses tend to develop abnormal behaviour when kept inside, such as cribbing, weaving, stall walking, and aggression. However, we’ve also heard that providing the horse with a toy or two and a hay net makes his life in the box stall a pampered one.

These are well-intentioned attempts to make the box nicer for the horse, but their effect is quite limited. Here are the facts about what these ‘enrichments’ actually do for the horse. I end with practical suggestions for housing that more closely suits the horse’s needs.

Welfare

We all want our horses to have a good life. That’s why we buy them treats and new brushes and fit their saddles and get blankets—and, all to often, bring them inside for the winter. Wanting them to have a good life is equivalent to wanting them to have good welfare. Welfare refers to quality of life—how easily a creature is able to adapt to its environment (Waran, 2002). If it is difficult or entirely impossible to completely adapt to the environment, the animal has poor welfare. If it can adapt and fit in, there is good welfare.

When horses show stereotypical behaviour (repetitive, abnormal behaviours like cribbing), aggression towards humans, behaviours caused by stress, or lack of engagement in the environment, these are attempts by the horse to cope with an environment that it doesn’t easily fit into. The presence of these four criteria can be used to assess welfare, and were used by Ruet et al (2019) in their study of housing horses in boxes.

It is easy to see how saddles illustrate this. A horse can never adapt its back to a poorly fitting saddle, and is likely to show aggression when it is put on and stress related behaviours when being ridden, so the saddle compromises its welfare. For a well-fitting saddle, however, the horse is adapted already, and its welfare is improved.

The same comparison may be made for any situation. Let’s see how it applies to box stalls.

Enriching the Box

The goal of enrichment is to make animals in an unnatural environment more likely to display the natural behaviours they would engage in in a natural environment. Bulens et al (2013) note that the most effective enrichment is providing something for the horse to eat, as 50-70% of their time is spent eating normally. In their study they used a bottle filled with sand and suspending from the ceiling, and a rope similarly suspended for the horse to play with. They found that the enriching effects of these objects were similar to other studies that looked at commercially available horse toys. Any beneficial effect was quite limited because they did not allow the horse to increase normal behaviour (locomotion, and interaction with other horses).

Ruet et al (2019) examined 12 factors in the lives of stabled horses: sex, age, time spent in the box, whether there was a window into the next stall, the bedding type, how much feed was given, how much concentrated feed was given, what discipline the horse was used in, the level of performance, the number of competitions, hours spent working per week, and lunging or walking time per week. Only three of these factors exhibited a positive change in the horse’s behaviour: straw bedding seemed to reduce aggression towards humans, a box with a window also reduced aggression, and less concentrated feed reduced repetitive abnormal behaviours, especially cribbing.

In short, enrichments weren’t as enriching as originally thought.

The Effect of Turn Out

Unresponsiveness to the environment, no longer showing interest in events or happenings around it, increases the more time the horse spends inside. This is shown by a withdrawn posture, where the head is level with the back, the ears do not move much, and the horse just does nothing (Ruet et al, 2019). While there is a place for horses to rest in a posture similar to this, this refers to an abnormal amount of time spent in this posture.

Horses that show stressed behaviours in the box, like pacing, calling out, or holding an alert posture for long periods are most likely to begin to slip into unresponsiveness, suggesting that these behaviours may be comparable to anxiety and depression (Ruet et al, 2019).

These behaviours are all reduced or non-existent when horses are studied at pasture with social interaction and space to move freely; to prevent this downward slide into poor welfare, avoid keeping a horse inside (Mills and Clarke, 2002).

Surviving Stall Rest

Horses that receive some turnout display the four indicators less often, showing an improvement in welfare, or at least a reduction in the deterioration of welfare caused by living inside (Ruet et al, 2019).

However, sometimes it is absolutely necessary to keep a horse confined inside, such as in stall rest. In this situation, using anything that may help the horse cope is advisable (Mills and Clarke, 2002). Allowing contact with another horse, providing a variety of food and a constant supply of fibre, keeping the lights on, and anything to keep the horse interested in the environment through sounds and sights can all help to reduce the negative welfare implications of forced stall rest.

We Live in Canada

What about when it is cold? The thermoneutral zone of horses, where there is no increased effort to maintain internal body temperature, is between -15 and 10 degrees Celsius in still air, and between 5 and 25 degrees Celsius under more normal environmental conditions (Morgan, 1998). Below 5 degrees the horse’s metabolism must increase to maintain internal temperature (Morgan, 1998). Providing continuous access to food to support the increase in metabolism along with adequate shelter is sufficient for the horse to maintain its internal temperature and body condition score over winter without compromising welfare (Mejdell and Bøe, 2005).

Conclusion

Horses were designed to live outside and express normal behaviour, to move freely in groups of other horses, to eat for most of the day, to avoid fear and distress, and to be able to avoid unpleasant or painful situations. While these ‘five freedoms’ have been criticized by some, they are still a good general guide (Mills and Clarke, 2002). The four factors used in Ruet et al’s (2019) study are also not all-encompassing and other factors and indicators should also be studied.

If your horse is quiet in the box, is he ‘good to stable’ or is he withdrawing from his environment?

If your horse chews any exposed wood, is he ‘trying to annoy you’ or expressing that his normal behaviours are being frustrated?

If your horse is vigilant and pacing in his box, is he ‘full of beans’ or on the road through anxiety to depression?

If your horse shows aggression towards you, is he being ‘naughty’ or coping with a suboptimal environment by letting the frustration out—towards you?

If you have the option, are you going to keep your horse inside and compromise his welfare, or let him be a horse as much as possible?

References

Bulens, A; Van Beirendonck, S; Van Thielen, J; and Driessen, B. (2013) The enriching effect of non-commercial items in stabled horses. Applied Animal Behaviour Science 143:46–51

Mejdell, CM and Bøe, KE. (2005) Responses to climatic variables of horses housed outdoors under Nordic winter conditions. Can. J. Anim. Sci. 85: 307–308.

Mills, DS and Clarke, A. (2002) Housing, Management, and Welfare. In: The Welfare of Horses: Waran, N (editor) Springer: Dordrecht, The Netherlands.

Morgan, K. (1998) Thermoneutral Zone and Critical Temperatures of Horses. J. therm. Biol. 23:1 pp. 59-61

Ruet, A; Lemarchand, J; Parias, C; Mach, N; Moisan, M-P; Foury, A; Briant, C; and Lansade, L. (2019) Housing Horses in Individual Boxes Is a Challenge with Regard to Welfare. Animals 9:621

Waran, N. (2002) Preface. In: The Welfare of Horses: Waran, N (editor) Springer: Dordrecht, The Netherlands.

Research

Are Horses Intelligent?

Before you say, ‘of course!’…

Intelligence

It is important to define words that can mean different things to different people. The word of interest here is ‘intelligence’. What is intelligence?

Jacques Lautrey (2004) has proposed this definition: “Intelligence is… the capacity of an organism—or of an artificial system—to modify itself to adapt its behaviour to the constraints of its environment… But this cognitive ability to adapt does not qualify as intelligence unless it is generalizable to a fairly high degree, that is, if it appears in different situations….”

Comparing Intelligence

While no scientist will agree with another on a definition, there seems to be a general consensus that every species is ‘intelligent’ in a certain way. There are many forms of intelligence. While the number and type of these forms is also debated, one scientist (Howard Gardner, 1985) proposed eight types, and observed that each species of animal had strengths and weaknesses in each of the eight types. Rats are spatially intelligent, for example, and birds are musically intelligent (Leblanc, 2013).

For this reason, comparing levels of intelligence between species (i.e. between horses and humans) is essentially meaningless. Comparing one horse’s strengths to another horse’s, or to the general horse population, is more meaningful than comparing a horse’s strengths with a human’s strengths to determine comparative intelligence (Leblanc, 2013).

Intelligence and Cognition

Now, the way we use the word ‘intelligence’ in everyday life really doesn’t make this matter any simpler. Depending on the context we use it in, it could mean many different things, from the ability to learn to possessing the power of reason. In scientific literature, ‘intelligence’ is typically used of behaviour that is begun by an innate response, such as an instinct, and allows the creature to make specific adaptations in response to specific problems (Vauclair, 1996). In contrast, they may use the word ‘cognition’ to describe the way an animal learns and processes information, allowing a creature to adapt to unpredictable changes in its environment. The distinction is subtle, but fairly important.

So, when an animal is able to adapt a response that it has learned already (as opposed to an instinctive response) to a new situation, and when the newly adapted response can itself be generalized to suit other new situations, the animal has cognitive ability (Leblanc, 2013).

Both intelligent responses and cognitive responses are observed in horses. When we speak of these mental abilities in relation to trained responses, however, cognition is the more accurate ability to measure.

A Helpful Way to Think about Intelligence

We may consider a horse to be intelligent if he learns a new concept easily (and by extension not intelligent if they do not learn quickly). However, training is influenced by at least eight massive variables: learning ability, the human’s knowledge and skill, the horse’s temperament, conformation, history, and health, and the training environment (McGreevy and McLean, 2010). It is more helpful, then, to think of controlling these variables rather than appealing to the horse’s intelligence.

Further, we may consider a horse to be intelligent if he seems able to read our minds. However, this is really a product of the eight variables above, where the horse has learned to recognize subtle cues. This is usually a result of the horse’s adeptness at making associations and generalizing (McGreevy and McLean, 2010).

Finally, a horse may be considered intelligent if he has learned behaviour that thwarts his handler’s wishes. This again, however, if a product of the eight influences on training, and is more an indication of how these factors have affected the horse’s environment than a reflection of the horse’s level of intelligence (McGreevy and McLean, 2010).

What this Means

In our interactions with horses, it is counter-productive to our goal (and our morale) to wonder if the horse is more or less intelligent than we are. What we should be most concerned about, in order to really understand our horses and relate to them better, is comprehending the horse’s cognition, which includes learning processes, mental capacity, and information processing (Leblanc, 2013). Understanding how these processes differ from ours will enable us to treat the horse as a horse—leading to improved welfare for the horse and greater success for us.

Conwy Lloyd Morgan (1894) proposed this principle, known as Morgan’s canon, which makes a great deal of sense even now: “in no case may we interpret an action as the outcome of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one that stands lower in the psychological scale”.

In other words, if your horse knocked you over with his nose, it is probably more accurate to say that he learned to push in order to receive food than that he is trying to get back at you for forgetting to bring treats.

References

Gardner, H. (1985) Frames of Mind: The Theory of Multiple Intelligences. New York: Basic Books.

Lautrey, J. (2004) Hauts potentiels et talents: La position actuelle du problème. Psychologie Française49:219-32

Leblanc, M. (2013) The Mind of the Horse. Cambridge, MA: Harvard University Press.

McGreevy, P and McLean, A. (2010) Equitation Science. West Sussex, UK: Wiley-Blackwell.

Morgan, CL (1894) Introduction to Comparative Psychology. London: Scott.

Vauclair, J. (1996) Animal Cognition: An Introduction to Modern Comparative Psychology. Cambridge, MA: Harvard University Press.