Many interventions and environments animals are exposed to cause us concern about the animals and their welfare. Examples include the confinement of housing, the relative unpalatability of certain feeds, or possible pain associated with procedures. But, when we discuss animal welfare, we often assume that we know what is best for the animals and we assume we know what they need. What is a behavioural need? How do we know that an animal's needs are not being met? People often say we should house calves or pigs or hens outdoors because they suffer when prevented from seeing natural sunlight. But, where is the evidence to support such arguments?
Human senses can be completely different from those of other animals, so our perception of an environment is inherently different from that of the animal concerned. Also, not surprisingly, we cannot be sure we have the same desires, motivations or mental processes as other animals, because non-human animals have evolved and been selected for different environments and purposes. Therefore, they have a variety of requirements, e.g., the chewing behaviour of dogs differs not only from other species, but may differ between breeds.
The motivation to perform certain activities can become aroused solely by internal factors. Plainly, the causal factors that increase motivation to perform searching behaviours are internally motivated. For example, if we restrict an animal's access to food, the animal will eat faster and for longer when food does become available than it would during a normal feeding bout with food freely provided. But this would not be the case for externally motivated behaviours such as a predator. If an animal is not exposed to a predator for a month, it does not run faster or farther away than if it saw a predator two days previously. So, searching behaviours give us an insight into the animal's motivation. We can broadly identify the resource that was being sought if we see less searching after the animal is granted access to the resource.
Another way, in which we can know that an animal's needs are not being met, is to look for so-called post-inhibitory rebound. What is rebound? When an animal performs a behaviour at a higher rate after deprivation, we call this rebound. It is only really expected when there are important internal factors and when the strengths of those internal factors increase with time. Again, this tells us something about the need to perform internally motivated behaviours.
The implications of these observations for welfare are that we can identify environments or husbandry systems that allow the animals to perform these internally motivated activities. For example, we should provide caged hens with enough room to flap their wings, because this behaviour shows a rebound when birds from small cages are put into pens that allow the behaviour. By failing to do so and providing suboptimal environments that prevent the expression of these highly motivated behaviours, we can push any animal into performing other behaviour patterns that are thought to indicate feelings of frustration. These include some abnormal behaviours, such as stereotypies. This will continue for as long as the animal is thwarted in its attempt to act out its strong motivational tendencies. Stereotypies themselves can show rebound. For example, if overgrooming is a coping strategy, preventing the overgrooming by means of Elizabethan collars or other devices, is likely to increase stress rather than to improve matters.
We have to gain an appreciation of how animals respond in different environments before we can use their behaviour as a key to understanding their preferences and motivation. Three methods have evolved to ask animals these questions: preference tests, operant techniques and consumer demand theory.
The simplest test to determine what an animal wants is the ordinary preference test. The experimenter offers the animal two different choices of environment, food, light, etc.
The measure of preference can be:
The time spent in or with each option with free access
The number of choices for each option
The number of choices for each option when the animal is confined after making a choice, so that its decision has some consequences
Simple preferences tests can be extended so that the animal is offered several variations on the one theme. The combinations of possibilities are almost endless - food, lighting, flooring, companions, etc.
A more advanced method of determining preferences is the operant test. The term 'operant' is used because the animal operates or manipulates some part of its environment to cause a change in its circumstances (e.g., a mouse might press a switch or run in an exercise wheel to activate a feeder that dispenses a preferred food). Various devices can be used, such as running on conveyors, nosing panels, pulling chains, etc. These can switch a light on or off, open a door to an outside pen, or adjust a source of heat or cold. In all these cases, the same results could be achieved by asking the animal to go through a T-maze preference test. So in reality, operant tests are really little more than sophisticated preference tests.
Preference and operant tests are nevertheless useful because they allow us to by-pass human interpretations about non-human animal preferences. They allow us to examine the end-point of the animal's perceptions and motivations for various aspects of its environment. However, they have several disadvantages.
1. Absolute vs. Relative Preferences
First, and most important, such tests can give only a measure of relative preference. They only tell us how much the animal likes A compared to B. This means there is no information regarding the absolute need for one of the preferences, or how much the animal is likely to suffer if one or both of them is not provided. For example, we might offer a whelping bitch both straw and paper strips so that she can nest. If she always chooses the straw, we can be sure that she prefers the straw. But when we provide her with paper strips she still nests. Does this mean she is suffering when we do not provide her with straw?
Similarly, when an animal makes a choice, there is no way of being certain that the selection is not simply the less aversive of the two options available. Neither of the alternatives may be what the animal would actively seek out, but the choice makes one preferable to the other.
2. Short-term versus Long-term Preferences
The second problem is that short-term preferences might not be the same as long-term preferences. An example of this is the motivation that hens have for a suitable nest site. If we place hens into a system that allows them access to a nest, but they are locked in the nest for several hours after they have chosen it, they still continue to choose the nest when they are offered it just before they are about to lay. This is despite their being deprived of feed and water for a considerable period after. So in this case, the short-term preference for a suitable nest site temporarily outweighs the long-term needs for food and water. This is not necessarily always the case.
3. Lack of Behavioural Wisdom
The third problem is that animals do not always choose what is best for their own long-term physical wellbeing. For instance, rats will consume large amounts of saccharine solution, although this has no nutritional value.
This means that preferences shown by animals can not be interpreted only in view of the long-term consequences they have on physical health. For example, a dog may have a bad experience on its first visit to the vet clinic and, because of this, it would inappropriately choose not to go in future. Similarly, the use of choice tests may be flawed by the effects of experience, since an animal that has been deprived of a resource all its life may not have any information about the medium-term benefits of that resource and, therefore, may be unable to make an informed choice.
4. The Tests Do Not Measure the Strength of Preference
Another important failing of choice tests of these types is that they do not require the animal to do much work and they do not measure the strength of the preference. In addition, if the animal is in a monotonous environment and is frustrated (bored), performing key presses and making choices may in itself be rewarding. The animal may press on a panel simply because it is something to do. Given that there are a number of problems with preference and operant tests, what are the alternatives?
Consumer Demand Theory
When preferences have been established, the animals can be made to pay a 'cost,' for example, having to peck a key or press a lever many times for the same reward to see whether it is still worth it for them. This is called consumer demand theory and it is useful because it allows us to work out the relative importance of different resources. If the animal's preference is still apparent when it has to work harder to gain access to its most preferred environment, the animal is said to show inelastic demand. This is a key concept for animal welfare science, because it provides a method of getting animals to show, through their behaviour, how important environments or commodities are to them.
Interesting test resources have included access to a variety of bedding materials, a number of degrees of social contact with conspecifics, cages of varying sizes and complexity, nests of varying sizes, and different designs of treadmill.
Cognitive bias refers to the tendency for humans and non-human animals to interpret events positively or negatively depending on their emotional state. It is therefore possible to use a measure of cognitive bias as an indicator of whether an individual may be feeling 'happy' or 'unhappy.' This has been tested in rats, sheep, chickens, starlings and dogs. In these species, positive changes in the individual's environment resulted in a cognitive bias towards positive outcomes (optimism), and negative changes in their environment resulted in a cognitive bias towards negative outcomes (pessimism). Measuring cognitive biases in animals gives us an objective insight into their current emotional state, which allows us to draw conclusions about what makes them 'happy' and what distresses them in the short term.
Humans are considered to display 'dispositional optimism' when they tend to expect positive outcomes more often than negative outcomes. Optimistic human individuals are typically considered to be less stressed and better able to cope with a large variety of stressful situations than more pessimistic individuals. It is possible animals also display optimism as a character trait, and if so, measuring cognitive bias over a long period may reveal it.
Dog personality traits have been studied, and it has been suggested that some may be similar to personality traits found in humans. Identifying links between optimism and personality in dogs may help to identify individual dogs with a high likelihood of successfully completing training for highly demanding jobs, such as police dogs or drug-detection work. A tendency towards pessimism may be linked with a high likelihood of developing anxiety-related behavioural problems.
Examining whether cognitive bias changes over time may aid in the early prediction of the likelihood of success for a dog in demanding training programs at an early age, and to identify appropriate training and behavioural modification approaches for dogs of different temperaments. It may also allow future researchers to streamline welfare studies by allowing individuals that are likely to be more or less sensitive than average to welfare concerns to be identified. Understanding how animal personalities affect tendencies towards optimism or pessimism and the demand for resources would permit fine tuning of the use of cognitive bias as a tool in animal training and welfare.