1.1. the Effect of the Visual Environment on Avian Welfare

one: introduction 1 1.1. The effect of the visual environment on avian welfare 1.1. Summary There is an increasing body of evidence showing that the vision of birds is significantly different from that of humans in many respects. Most behavioural research so far has concentrated on the ecological functions of these differences, in particular the role of ultraviolet (UV, referring to UVA portion of spectrum, 320-400 nm) vision in behaviours such as mate choice and foraging (see review, Cuthill et al. 2000b). It is clear that the appearance of objects and conspecifics affects many aspects of bird behaviour. The appearance of an object depends not just on the visual system of the viewer, but on the characteristics of the illuminating light and the degree to which that object reflects or absorbs the light falling upon it. In sensory ecology, we assume that the visual systems of animals are adapted to making visual discriminations under the range of lighting conditions found in their natural habitats (Lythgoe 1979; Barth and Schmid 2001). However, we frequently keep birds indoors in farms, zoos and laboratories, under artificial light in visual environments that are quite unlike natural visual scenes. Most artificial lighting is UV deficient. Also, conventional fluorescent lights flicker, albeit at a level above that which most humans can perceive. Given that that birds can perceive UV (reviewed by Cuthill et al. 2000b) and may have better motion perception than us (D'Eath 1998; Fleishman and Endler 2000), such lighting may limit the functionality of their visual systems and impair their welfare (Sherwin et al. 1999; Maddocks 2001; Greenwood et al. 2002; Maddocks et al. 2002c). Also, experiments performed under these conditions may have poor external validity1, as may experiments in which the animal looks at computer or video monitors as stimuli (D’Eath 1998; Fleishman and Endler 2000). 1 The extent to which the results of an experiment can correctly be generalised to other circumstances one: introduction 2 There is a substantial body of research into the effects of different light sources and different lighting regimes on birds. Most of this work has been on poultry, and has either focussed on trying to maximise growth or egg production, or minimising aberrant behaviours such as feather pecking and cannibalism (see reviews, Manser 1996; Lewis and Morris 1998; Maddocks 2001). Studies assessing the effect of light environments on general welfare are rarer, and often produce conflicting or inconsistent results. This is partly because different studies use different methods, timescales and sample sizes with which to assess welfare, and partly because the interpretation of many studies is problematic as more than one experimental lighting variable has been manipulated simultaneously (Maddocks 2001). This thesis concentrates on whether or not the absence of UV, or the flicker rate of conventional fluorescent light, adversely affects bird welfare. The aim was to run tightly controlled experiments which, unlike most previous studies, were not confounded by the simultaneous manipulation of several variables, and controlled for the sensitivity of birds to UV light as well as their sensitivity to human visible wavelengths. As the only way to accurately assess welfare is to use a range of behavioural, physiological and health measures (Dawkins 1990; Broom 1991; Appleby and Hughes 1997; Broom 2001), welfare has been assessed using a variety of welfare indicators, namely preferences, behavioural measures and blood plasma levels of the major ‘stress’ hormone in birds, corticosterone. In this review, there are five main sections. In section 1.2., I discuss what animal ‘welfare’ means and describe how welfare may be measured. This includes a consideration of the philosophical problems underlying the assessment of animal welfare. As biologists often choose to measure stress as a potential welfare indicator, in section 1.3., I discuss the meaning and measurement of ‘stress’. I then turn to the two parameters of light environments whose effects I have investigated. In section 1.4., I describe the differences between human and avian colour vision and explain why the absence of UV in standard artificial lights may adversely affect bird welfare. In sections 1.5. and 1.6., I discuss what is known about the sensitivity of humans and birds to repetitive visual stimulation, both from the flicker from fluorescent lamps and from spatially repetitive elements in the visual surround, and the potential welfare effects of such stimuli. I have one: introduction 3 not covered the effects of light intensity, photoperiod or different types of light source on bird welfare and productivity, as these aspects of lighting are not central to the topic of this thesis, and recent reviews on these subjects already exist (see Lewis et al. 1992; Manser 1996; Lewis and Morris 1998; Maddocks 2001). Section 1.7. summarises the main points of the previous sections and explains why the research in this thesis was carried out. 1.2. Welfare assessment 1.2.1. The meaning and measurement of ‘welfare’ Animal ‘welfare’ is a term that has sprung from the increasing concern of society about the treatment of animals and their quality of life (Fraser et al. 1997). The public looks to science for guidance in their concerns. However, animal welfare is not a purely scientific concept and involves value judgements that differ between people (Duncan and Fraser 1997). This means that firstly it is hard to formulate a concrete definition of the term, and that secondly that entirely objective welfare assessment is difficult to achieve (Clark et al. 1997a; Bath 1998; Webster 1998). Our interest in animal welfare springs from the moral concern we feel for animals. This is based upon the belief that they have the capacity for subjective experience, in particular the concern that they may be able to suffer, that is to experience unpleasant subjective feelings (Broom and Johnson 1993). For example, unless we are prepared to extend our concerns to plants, it would not matter on a moral level if an animal was underweight, or injured, if it had no awareness of hunger or pain (Duncan and Fraser 1997). Whether or not an animal possesses awareness of such things will depend on its sensory and cognitive capacities. For example, pain in humans seems to have both a sensory and cognitive component, and without both components intact humans do not suffer from pain. Some humans with nerve damage cannot feel noxious stimuli that are damaging to tissue (Bateson 1991). However, humans whose sensory inputs are intact but who have had the frontal lobes of their cerebral cortex removed may report that they can feel pain but it no longer bothers them (Sweet 1971). Although it is possible that many animals do not have the requisite sensory and cognitive abilities to one: introduction 4 suffer in the sense that humans experience suffering, most people believe that animals can experience emotions and feelings, and that they can experience pleasure if their life is good, and suffer if conditions are bad. Hence the capacity of animals to experience suffering and enjoyment is a fundamental concern in the study of animal welfare (Dawkins 1988; Rollin 1992; Sambraus 1998; Dawkins 2001a), and some say that in fact it is the only issue (Duncan 1993). Welfare also includes assessing the health and state of behavioural and physiological coping mechanisms of the animal (Broom 1986, 1996, 1998, 2001; Dawkins 2001a). That said, although disease and injury are universally recognised as being signs of poor welfare, evidence from the human literature suggests that individual perception of welfare and happiness is not correlated strongly with physical health, being more reliant on the temperament, expectations and degree of social support and control over their life each individual has (Lutgendorf 2001). Welfare therefore depends partly on subjective states that correspond to how animals feel (Duncan 1993; Dawkins 1998), and partly on their state of health (Broom 2001). Welfare can be conceptualised as a multi-dimensional state of well-being, or characteristic of an animal, that can vary along a scale from being very poor to very good (Broom and Johnson 1993; Broom 2001). Although this is a helpful concept, sometimes individual welfare indicators may not always vary along a simple continuum, as indicators of poor welfare may not be simply the opposite of indicators of good welfare (Knierim et al. 2001). Alternatively, good welfare can be conceptualised as the degree of evolutionary fitness which the animal possesses, i.e. the degree to which the animal is ‘on track’ to survive and reproduce (Dawkins 2001a). However, if fitness is defined as reproductive success, animals with high fitness do not necessarily have better welfare than those with low fitness (Jensen 2001). There are no absolute standards or definitions, as animal welfare is a multidimensional concept involving many factors for which there is no obvious combining or weighting formula (Fraser 1995). The measurement of any element of welfare is essentially a measure of quality of life, with peoples’ values determining how much importance they place on any particular measure (Duncan and Fraser 1997). In order to suffer from any given factor, an animal needs to be aware of its experience and have unpleasant feelings about it. Suffering would almost certainly increase if the animal could mentally ‘travel through time’, and remember specific unpleasant events, one: introduction 5 and also anticipate future unpleasant events. This means that when making a welfare judgement based on an animal’s feelings one has to consider the cognitive capacities of the animal, and confront the difficult question of whether or not the animal is conscious of or aware of anything (Dawkins 1998). However, poor welfare can also be considered to occur in the absence of negative feelings or suffering, for example if the animal has a disease but is unaware of it (Broom 2001).

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