Swimming speeds and prey selection of temporally captive, wild grey seals (Halichoerus grypus) were investigated in relation to prey characteristics in an experimental set-up at the Sea Mammal Research Unit (St Andrews, UK). For breath- hold divers, such as seals, the cost of swimming is a key variable in the management of oxygen stores. Thus it is likely that they modulate their swim speeds in order to maximise time spent feeding at a prey patch. We observed a strong relationship between swimming speed and stroke and glide pattern. Seals decreased their swim speeds by increasing their gliding period and as a result they decreased their oxygen consumption. Results indicated that mean swim speed decreased significantly with increasing distance to the patch, consistent with optimality model predictions. In addition, seals modified their swim speeds in response to changes in the speed and density of their prey. Seals decreased their swim speed as the speed of the prey increased. On the other hand, seals increased their swim speed as the density of the prey increased. Concurrently, bottom durations significantly increased suggesting that seals’ foraging strategies allowed them to most efficiently exploit their environment. Prey selection experiments investigated dietary preferences and the factors affecting their choice to select between different types of food. In the present study, seals maximised some aspects of their energy intake but also displayed some individual prey preferences. These findings indicate the importance of fine-scale observations of foraging behaviour and the value of experimental protocols in developing our understanding of marine mammal foraging behaviour.

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A period of 15 months was spent studying the behaviour and ecology of Indri indri in the eastern rain-forest of Madagascar. Two groups were habituated to the observer and followed every six weeks for a complete year. Quantitatives sampling techniques were developed which allowed several animals' behaviour to be simultaneously recorded. Surveys were conducted in three areas of different botanical and topographical structure and censuses performed both at the beginning and end of the study. Some behavioural properties of a population of Indri were investigated in one study site by collecting data on vocal interactions between approximately 40 groups. The maintenance activities of the species are described and assessed. Seasonal and individual variation in behaviour are compared both in the groups studied and with other species. Social behaviour is analysed (1) by measures of animal interaction and (2) in terms of the inter-dependence of some individuals' behaviour with others. Measures of spacing and feeding are shown to be suitable to this approach. Evidence for the territoriality of the species is presented and its adaptive qualities considered. The roles of territory definition, declaration and occupation are contrasted and compared. The development of behaviour in infant and juvenile Indri is examined in terms of individual and social adaptations. Some facets of ecological and social differentiation with Indri society are proposed.

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