Animal welfare and consumer demand theory: Are preference tests a luxury we can't afford?

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Goss-Custard, unpublished data), reduction in interference seems a more probable benefit from defending feeding areas in this species. Clearly, this work needs to be repeated in other species and places. We publish these results partly to point out that some waders are very good birds to test ideas on the benefit foraging animals derive from defending feeding space. Only a proportion of the population defend territories so that comparisons can be made between territorial and non-territorial individuals. Furthermore, the territories are held at a time of year when death from starvation, particularly in the redshank (Baillie 1980; Davidson 1982; Goss-Custard et al. 1977), is high and so the selection pressure to feed effectively is likely to be strong. We would like to thank S. E. A. le V. dit Durell for drawing the figure and Dr J. P. Dempster, D r M. G. Morris and J. Selman for comments on the manuscript. J. D. GOss-CUSTARD A. M. NICHOLSON S. WINTERBOTTOM Institute of Terrestrial Ecology, Furzebrook Research Station, Wareham, Dorset, BH20 5AS, U.K. References BaiUie, S. 1980. The effect of the hard winter of 1978[79 on the wader populations of the Ythan estuary. Wader Study Bull., 28, 16-17. Davidson, N. C. 1982. Changes in the body condition of redshank during mild winters: an inability to regulate reserves. Ring. Migr., 4, 51-62. Dugan, P. J. 1982. Seasonal changes in patch use by a territorial grey plover: weather dependent adjustments in foraging behaviour. J. Anita. EcoL, 51, 849-857. Goss-Custard, J. D. 1970. Feeding dispersion in some overwintering wading birds. In: Social Behaviour in Birds and Mammals (Ed. by J. H. Crook), pp. 3-35. London: Academic Press. Goss-Custard, J. D. 1976. Variation in the dispersion of redshank, Tringa totanus on their winter feeding grounds. Ibis, 118, 257-263. Goss-Custard, J. D. 1977a. The energetics of prey selection by redshank, Tringa totanus (L.) in relation to prey density, d. Anita. EcoL, 46, 1-19. Goss-Custard, J. D. 1977b. Predator responses and prey mortality in redshank, Tringa totanus (L.), and a preferred prey, Corophium volutatar (Pallas). d. Anim. Ecol., 46, 21-35. Goss-Custard, J. D., Jenyon, R. A., Jones, R. E., Newberry, P. E. & Williams, R. le B. 1977. The ecology of the Wash. II. Seasonal variation in the feeding conditions of wading birds (Charadrii). J. appl. EcoL, 14, 701-719. Myers, J. P., Connors, P. G. & Pitelka, F. A. 1979. Territory size in wintering sanderlings: the effects of prey abundance and intruder density. Auk, 96, 551-561.

(Received 11 April 1984; revised 22 June 1984; MS. number: sc-201) Animal Welfare and Consumer Demand Theory: Are Preference Tests a Luxury We Can't Afford? Marian Dawkins' (1983) recent paper contained an excellent discussion of 'ethological needs'. However, her application of an economic analogy, consumer demand

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theory, to bolster the precarious preference test method-. ology used to measure these needs, seems fraught with danger. I have several serious misgivings, both on the use of this analogy in particular and preference tests in general. Analogies are useful only if they lead us to new insights into behaviour. Some examples of the successful application of analogies in ethology are McFarland's (1971) use of control theory a n d the sociobiologists' adoption of game theory (Maynard Smith 1979). However, the application of consumer demand theory to animal welfare is dangerous because it introduces the emotive new terms 'luxury' and 'necessity' to classify behaviour, but without any corresponding new insight into their causation. In particular, the term luxury invokes subjective feelings that a behaviour pattern is frivolous, trivial or irrelevant, a concept which seems at odds with the idea that behaviour is adaptive and improves fitness. No doubt the two terms describe behaviours at the extremities of a continuum, and if so, it seems unproductive to classify them into such discrete categories, with misleading labels, when the middle of the continuum, and the interactions there, are probably more interesting and important anyway. Dawkins' analogy also appears to be post hoc justification of the experimental methodology. One of the first criticisms of preference tests was that they gave information on relative and not absolute preferences (Duncan 1978). Dawkins is aware of this criticism and has previously attempted to measure strength of preference by offering loaded choices to birds, such as an open run versus a battery cage with food (Dawkins 1977). Thus, the economic analogy clearly was not necessary to stimulate this type of experiment. My feeling is that the experimental design and the interpretation of results in this paper would have been the same regardless of consumer demand theory. However, any argument on the usefulness of economic analogies is unimportant in comparison with the fundamental problems that plague preference tests. I have six main criticisms of this method of assessing animal welfare. But first I must distinguish between the two common types of preference test. Type 1 (e.g. Dawkins' experiment 1) is a T-maze where responsiveness to two different environments is measured by locomotion: the bird 'votes with its feet'. Type 2 (e.g. Dawkins' experiment 2) is where a bird is allowed access to two adjacent environments and time spent in each is recorded. In consumer language, type 1 tests offer access to a commodity and type 2 the opportunity to consume it. My criticisms are as follows. (1) Preference tests are a point sample taken at a time when an animal's different motivational systems are variously stimulated to an unknown extent. Thus, preference tests do not measure strength of motivation because preference is clearly not equivalent to motivation when several motivational systems are simultaneously aroused. I am not even sure that they measure strength of preference when only one motivational variable is manipulated experimentally (in Dawkins' case it is food). To be confident of this I think multiple tests are required with both motivational variables under experimental control and set at different levels. (2) Preference tests are an inappropriate method for measuring responsiveness to conflicting stimuli such as food and dust because the bird (in type 1 tests) is given the choice of responding not with feeding or dustbathing behaviour, but with locomotion. For example,

SHORT COMMUNICATIONS I have found no variation in an operant response (lever lifting) to gain access to a commodity (straw for pregnant sows), but I have found variation in the response of pigs towards that commodity, from no response, to eating the straw, to nest building behaviour (Hutson, unpublished data). Or, to adopt the consumer analogy, I may buy cigarettes because I need them, i.e. I have a nicotine deficit, but at any particular time I may not consume them because I am sitting in the cinema, or my friend dislikes smoke, or I feel ill or guilty, etc. Thus, results from type 1 tests should be treated with extreme caution as they appear to be the least sensitive measure of motivation. (3) In Dawkins' experiment 2 the motivation to perform feeding is manipulated experinqentally while the motivation to dust-bathe presumably remains more or less the same. Yet, in the choice test only one behaviour, feeding, is measured. Why? Presumably, dust-bathing is not recorded because it occurs so rarely. A bird on average performs one 27-min bout every second day (Vestergaard 1982). Thus, the method tells us something about the strength of feeding motivation, but nothing about the strength of dust-bathing motivation, because the behaviour has not been measured. An improvement to this method has been suggested above: experimentally manipulate both motivations and then test in the type 2 choice test apparatus. But, how does exposure to dust and non-performance of dust-bathing behaviour in the choice test affect subsequent dust-bathing motivation ? A further improvement could be to ask the animal to perform an operant response to gain access to food or litter, and then measure responsiveness to the stimuli. (4) Preference tests often put the wrong question to the animal. For example, if we are interested in assessing the welfare needs of nesting hens and offer them choices between empty boxes and boxes of straw we may be making the wrong assumption and offering inappropriate alternatives. What the hen may really need is a box full of earth in which to make a scrape rather than to build a nest ! (5) The conflicting motivations are tested simultaneously. It seems equally important to test the relationships between dust-bathing and feeding before, during and after eating, and before, during and after dustbathing. When does a luxury become a necessity, and at what level of satiation of the conflicting motivations? In other words, the interest lies in the interactions between motivational systems. (6) Reducing the time available to perform frustrated behaviour patterns may be a suspect methodology if the behaviour patterns in conflict require different performance times. Thus a complete sequence of dust-bathing movements may be necessary to achieve a functional result whereas a brief feeding bout may achieve an equivalent functional effectiveness. Will a bird embark on a long dust-bathing sequence if it is aware that there is only a limited amount of time available to perform it in ? It also seems worthwhile to note in passing that other options in response to income reduction (e.g. cheating, stealing) are not available to birds in this type of experiment. Finally, I think that the title of Dawkins' paper is misleading when it suggests that battery hens have named their price: clearly, they have not. I think that all my comments and criticisms point to one general conclusion: that preference tests are luxuries that we, as ethologists, cannot afford. The real necessity is to measure motivation of animals to perform different behaviour patterns, in natural and confined environments, and when the con-

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flicting motivational systems are under satisfactory experimental control. G. D. HUTSON

School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia. References Dawkins, M. 1977. Do hens suffer in battery cages? Environmental preferences and welfare. Anim. Behav., 25, 1034-1046. Dawkins, M. t983. Battery hens name their price: consumer demand theory and the measurement of ethological 'needs'. Anim. Behav., 31, 1195-1205. Duncan, I. J. H. 1978. The interpretation of preference tests in animal behaviour. Appl. Anita. Ethol., 4, 197-200. Maynard Smith, J. 1979. Game theory and the evolution of behaviour. Proc. R. Soc. Lond., B, 205, 475-488. McFarland, D. J. 1971. Feedback Mechanisms in Animal Behaviour. New York: Academic Press. Vestergaard, K. 1982. Dust-bathing in the domestic fowl---diurnal rhythm and dust deprivation. Appl. Anita. Ethol., 8, 487-495.

(Received 30 April 1984; revised 20 June 1984; MS. number sc-206) Reply to Hutson G. D. Hutson (1984) is labouring under a number of misapprehensions. First of all, he makes the mistake of thinking that to call a behaviour a 'luxury' is to imply that it is frivolous or non-adaptive. Contrary to what he thinks, however, assigning differing degrees of elasticity reflects the adaptiveness of an animal's system of motivational priorities. Consider a population of animals that is in constant danger of dying of starvation but not of death through predation because there are very few predators around. Variation among these animals in their ability to find food (and the priority they give to food finding) would therefore be reflected in variation in their survival and reproductive success. Variation among them in ability to get away from predators (and the priority they give to keeping a look out for them) would affect their fitness to a much smaller extent. In a well-adapted animal in such an environment, we would expect that food-finding would show inelastic demand (necessity), whereas scanning for predators should show elastic demand. The well-adapted animal is expected to give highest priority (most inelastic demand) to doing behaviour which, if it did not do it, would be most likely to lead to its death or reproductive failure. It should give lowest priority (most elastic demand) to behaviour where failure to do it has the least effect on fitness (ef. McFarland & Houston 1981). Despite what Hutson seems to think, economic analogies of this sort are in tune with, not incompatible with, ideas about the adaptiveness of behaviour. Secondly, he dismisses economic analogies as not contributing anything of value and then criticizes preference tests as misleading in animal welfare studies. What he fails to realize is that the whole point of introducing an economic approach to animal welfare is to overcome the objections that can (and already have been) raised to the simpler kind of preference test. For example, h i s first objection to preference tests is that a single test between two alternatives does not deal with the problem of corn-