David McFarland

Decision making in animals

Animals must make decisions about when to feed, when to court, when to sleep, and so on, in such a way as to maximise as far as possible their chances of survival and reproductive success. It is possible to formulate in mathematical terms the optimal strategy for an animal to pursue. The theoretical optimum behaviour can be compared with the actual behaviour of the animal, and perhaps shed some light on the evolution of behaviour.

ON THE FITNESS OF BEHAVIOR SEQUENCES

Our aim is to demonstrate a method of determining the extent to which behavior maximizes fitness. We believe the temporal organization of behavior to be in part dependent on the animals genetic makeup and subject to natural selection and that behavioral strategies may be as adaptive as structural characters. The question of the adaptiveness of behavior has been found hard to study in the past (Tinbergen 1963) because of the difficulty of quantitative verification of hypotheses. The method presented here tests specifically whether deployment of behavioral options is optimally related to environmental conditions.

Kinship and altruism: A cross-cultural experimental study

Humans are characterized by an unusual level of prosociality. Despite this, considerable indirect evidence suggests that biological kinship plays an important role in altruistic behaviour. All previous reports of the influence of kin selection on human altruism have, however, used correlational (rather than experimental) designs, or imposed only a hypothetical or negligible time cost on participants. Since these research designs fail either to control for confounding variables or to meet the criteria required as a test of Hamiltons rule for kin selection (that the altruist pays a true cost), they fail to establish unequivocally whether kin selection plays a role. We show that individuals from two different cultures behave in accordance with Hamiltons rule by acting more altruistically (imposing a higher physical cost upon themselves) towards more closely related individuals. Three possible sources of confound were ruled out: generational effects, sexual attraction and reciprocity. Performance on the task however did not exhibit a perfect linear relationship with relatedness, which might reflect either the intrusion of other variables (e.g. cultural differences in the way kinship is costed) or that our behavioural measure is insufficiently sensitive to fine-tuned differences in the way individuals view their social world. These findings provide the first unequivocal experimental evidence that kinship plays a role in moderating altruistic behaviour. Kinship thus represents a baseline against which individuals pitch other criteria (including reciprocity, prosociality, obligation and a moral sense) when deciding how to behave towards others.

The cost of changing from one activity to another.

When there is a cost of changing from one activity to another it affects the temporal organization of behaviour. It is shown theoretically that the cost of changing should be allocated by an animal to the cost of the behaviour that is about to be performed. This hypothesis is confirmed for the Barbary dove (Streptopelia risoria) changing between feeding and drinking in an experimental room. The double interruption method is used to determine the position of dominance boundaries in food and water deficit space. Boundary rotation is used to determine how a cost of changing affects motivational state and therefore how the cost is allocated. Results obtained in the room experiments are shown to be comparable to results obtained in Skinner boxes in which the double interruption and dominance boundary methods have been previously used, supporting their validity.

A demanding task: using economic techniques to assess animal priorities.

Copyright 1998 The Association for the Study of Animal Behaviour.

‘Unitary drives’ revisited

Abstract The consequences of an animals behaviour depend, in part, upon the nature of the environment. When the consequences affect the motivational state in a non-unitary manner, the environment is said to be ambivalent. Certain consequences of behaviour, and therefore certain goals are said to be unrealizable when they cannot be attained as a result of environmental ambivalance. In such situations animals attempt to approach as close as possible to the goal, by means of some optimization procedure. Because some optimality principles may require the same behaviour in different situations, it is not always legitimate to infer motivational changes from the observed behaviour. In such cases the motivational state is said to be unobservable. The overall observability of a motivational system is related to the number of dimensions in which the goal is realizable.

Water conservation by inhibition of food intake.

Abstract Bodyweight, food and water intake, faecal water loss, and rectal temperature, in the Barbary dove, were measured daily during ad libitum food and water intake, water deprivation, and food deprivation, at controlled environmental temperatures. Water intake, water loss, and rectal temperature fall markedly during food deprivation. During water deprivation there is a decline in food intake and in rectal temperature. Rectal water loss is found to be a linear function of food intake, and the inhibition of food intake is thus an important means of water conservation during water deprivation. Measurements taken at 20°C and at 30°C suggest that ambient temperature has a primary effect on drinking, and that water loss is secondary.

Interaction of hunger and sexual motivation in the male rat: A time-sharing approach

Abstract To examine the interaction of hunger and sexual motivation, male rats were given sexual behaviour tests under 0, 24, and 48 h of food deprivation. Each male was placed with an oestrous-induced female and allowed to copulate until sexual exhaustion. Food was freely available throughout the test period. Mount and intromission latencies increased under both levels of food deprivation, but neither ejaculation frequency nor any of the other fourteen measures of sexual behaviour were altered under deprivation conditions. There was a decreased latency to start eating, an increase in time spent eating, and an increase in the amount of food eaten with increased food deprivation. The frequency of feeding bouts increased, but the duration of feeding bouts was constant over deprivation conditions. Under food deprivation, animals shifted from sexual behaviour to feeding more frequently than when they were non-deprived. These shifts occurred primarily during periods of low sexual arousal. The majority of feeding occurred during the post-ejaculatory intervals. Bouts of sexual behaviour were not usually interrupted by bouts of feeding. This pattern suggests that feeding and sexual activity occur on a time-sharing basis with sexual behaviour as the dominant activity.

Sleep in the Herring Gull (Larus argentatus)

Abstract Sleep postures and eye state of free-ranging herring gulls ( Larus argentatus ) were studied during the breeding season. Three mutually exclusive behaviours were observed, namely sleep, rest-sleep and rest postures. Arousal thresholds, eye blink rates and eye closure time were obtained during these behaviours. Significant relationships existed between eye blinking, eye closure, and a raised threshold of arousal when birds were in the sleep and rest-sleep postures. During a natural disturbance, birds in the sleep posture remained in this posture but did not blink their eyes: this is called pseudo sleep. Male gulls also exhibited a lower threshold of arousal while in the sleep posture compared with females. We conclude that rhythmic eye blinking is a good indication of sleep in herring gulls.

On the measurement of motivational variables

Abstract This paper discusses some problems concerning the measurement of behaviour variables in general. However, to place the issues in context, discussion is centred on recent ethological work on the interaction of internal and external factors in determining behaviour. In particular, it is maintained that it is not meaningful to postulate that such factors add or multiply, but that the optimal ordering of causal states is the issue upon which attention should be focussed.