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No description available.

Imagine a zebra in the African savannah. At each moment in time this zebra has to weigh up alternative courses of action before deciding which will be most beneficial to it. For instance, it may want to graze because it is short of food, or it may want to head towards a water hole because it is short of water, or it may want to remain motionless in order to avoid detection by the predator it can see lurking nearby. This is an example of the problem of <i>action selection</i>: how to choose, at each moment in time, the most appropriate out of a repertoire of possible actions. This thesis investigates action selection in a novel way and makes three main contributions. Firstly, a description is given of a simulated environment which is an extensive and detailed simulation of the problem of action selection for animals. Secondly, this simulated environment is used to investigate the adequacy of several theories of action selection such as the drive model, Lorenz's hydraulic model and Maes' spreading activation network. Thirdly, a new approach to action selection is developed which determines the most appropriate action in a principled way, and which does not suffer from the inherent shortcomings found in other methods.

The aim of this study, carried out on the Ythan estuary, Aberdeenshire, between October 1973 and June 1976, was to investigate the processes, if any, operating to regulate the numbers of wading birds with respect to food availability in winter. Data were collected on the numbers and distribution of all waders using the estuary throughout the year and detailed observations were made on the feeding, dispersion and aggressive behaviour of Redshank. It was found that the distribution of several species of waders on the estuary varied seasonally. Most of the Redshank were found in the top end of the estuary when numbers were low or when daylength was short, suggesting that this area was preferred. An extensive sampling programme for the invertebrate prey of Redshank failed to show any seasonal changes in the abundance of invertebrates which might account for the overriding influence of daylength on the distribution of Redshank. However, observations of feeding Redshank in several areas of the estuary showed that the calorific intake per minute, and per feeding movement, were greatest in the preferred area throughout the year. Corophium and Nereis were found to dominate the diet, both numerically and in terms of biomass, in all areas; however, it appeared that Nereis was the more important prey since, in the two areas of the estuary which were studied in the greatest detail, the variation in the calorific intake from Nereis explained a very large, percentage of the variation in total calorific intake. Observations of the dispersion and intra-specific aggression of Redshank suggested a mechanism whereby the density of birds feeding in winter might be regulated with respect to food availability. It is proposed that, through increased intra-specific aggression and the holding of feeding territories, Redshank spread out) over the estuary in winter causing some Redshank to feed in sub-optimal areas'). The possibility that such regulatory mechanisms are widespread amongst wading birds wintering in Britain is considered.

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The formation and function of mixed-species wader flocks in fields in Aberdeenshire were studied during 1976-79. Four species - oystercatchers, lapwings, redshank and golden plover - were common in fields in winter, and fed frequently in mixed flocks. Flocks of waders congregated in fields with high prey densities and experiments with model lapwings and oystercatchers showed that the four species were attracted to fields where other waders were feeding. These findings suggest that mixed flocking in waders facilitates the location of favourable feeding areas. The ingestion rates of oystercatchers, lapwings, redshank and golden plover were measured to test the hypothesis that, on the feeding grounds, members of wader flocks interact with each other in some beneficial way to increase their feeding efficiency. With one exception, the ingestion rates of waders were unaffected by changes in flock size, density and composition. Lapwings in conspecific groups of 2 - 10 fed at faster rates than those in groups of other sizes, but the reasons for this were not identified. These results show that waders did not increase their feeding efficiency by foraging in flocks. The dispersion patterns of the four species and the types of interference that waders incurred by feeding in flocks were examined. Differences in dispersion patterns between the species were not correlated with methods of hunting. Aggressive interactions between conspecifics occurred frequently in dense flocks, but interspecific encounters were rare. The plovers were parasitised heavily by black-headed and common gulls during the day, but not at night, when feeding also took place. Ways in which plovers could minimise the risk of sustaining gull attacks were investigated. The time that waders devoted to being alert did not change with flock size and composition, but individuals probably gained some protection from predators by feeding in mixed flocks.

The feeding ecology of red deer (Cervus elaphus) living in a Mediterranean environment was investigated. Composition of the diet was determined from the n-alkane content of samples of faeces. Principal Component Analysis and Canonical Variate Analysis were conducted on n-alkane concentrations of samples of vegetation. These multivariate statistical techniques demonstrated that n-alkanes could be used as markers to distinguish browse from herbage and individual browse species from each other, in such a way that n-alkane content of the faeces could be used to determine the composition of the diet of red deer. Red deer included grasses and forbs in their diets throughout the period of study, but the proportion of these groups of plants was lower in autumn when their availability was low. During autumn red deer included a high proportion of acorns in their diets. Browse was included in the diet mainly in summer, although a proportion of browse was found in the diet during other periods of the year. Females had a significant higher proportion of grasses and forbs in their diets during summer than males. OM digestibility of the diet was higher in spring and early summer but low in late summer and autumn. It is likely that the low total biomass of grasses and forbs constrained the opportunities for diet selection in late summer and autumn, whilst low availability of live plant material constrained the opportunities for diet selection in mid summer. In a Mediterranean environment red deer has to face relatively quick changes in the quality and quantity of food. In these environments red deer is probably subjected to different seasonal constraints on food availability compared to red deer at more northern latitudes. This could possible affect their reproductive cycle and ultimately population dynamics differently.

Oystercatchers care classified together with other waders in the Charadriiformes. These birds all have features that enable them to live successfully in semi-aquatic habitats. Most are more or less restricted to the littoral zone throughout their lives. Until recent times shore birds, Cyster catchers have begun to breed inland in certain parts of their range. Buxton (1961) and Dare (1946) have shown that there has been an increase in the numbers of this species breeding inland in Britain, particularly within the last 30 years. Falla (1966) mentions a similar increase In New Zealand and Hulscher (pen. comm.) reports an extension of their range into North Holland. Baemctopus ostrcilegus longlpes breeds inland on the steppes of Central Russia (Crote, 1931). The use of coastal fields by Oystercotchers in winter also appears to be increasing 0>arer 1966). At present it may only be of localised occurrence being reported from Glamorgan, Lancashire and Aberdeenshire. Consideration of the above points leads to the question - What factors have been responsible for the increase in the use of Inland habitats? It is not possible to study the causes of post events; thus the problem may be approached by Investigating the respective survival values at the present time of breeding Inland and the use of fields In winter. If It is found that advantages are conferred on those birds Involved In these newly acquired habits, then It may be possible to suggest mechanisms underlying the recent changes In habit. The present study was designed to answer the following questions: 1. To what extent do birds feed in fields in winter and what is the resulting survival value? 2, Is there an advantage in breeding inland?

Herring gulls, a colonial-nesting coastal bird, have increased dramatically in numbers in many parts of the British Isles during this century. The resulting increase in the size and distribution of breeding colonies has resulted in drastic changes in the vegetation of such sites. This study, in which equal emphasis was placed on both the gulls and the vegetation, was an attempt to determine the relationship between herring gulls and the vegetation of their nesting and roosting sites and in particular to account for the factors controlling such vegetation. Observations in gull breeding colonies revealed four principal bird activities affecting the vegetation of breeding sites: treading; the collecting of nest-material; boundary clashes associated with gull territorial behaviour; and defecation. The observations, supported by. field experiments, suggest that the disturbance and destruction of vegetation associated with boundary clashes is a particularly significant activity. A primary attribute of the plant species occurring in gull colonies is an ability to cope with such disturbance. The other gull activities are also of importance, though the study reveals that nutrient enrichment by defecation is often local in its effect, and of less importance than generally thought. Because of this regimen of environmental factors imposed by gulls - which in terms of their effect on vegetation become suppression, destruction and disturbance, and nutrient enrichment - normal coastal vegetation, often a fescue or thrift-dominated sward, is displaced by seasonal species- poor communities in which annuals and ruderals predominate. Annuals are in fact particularly well-adapted to take advantage of the bare areas resulting from repeated disturbance. Close examination of the distribution of plant species and of gull activities within colonies suggests that, although gulls are responsible for the vegetation of their colonies as a whole, factors other than gull activities play a more significant role in determining the precise distribution of plant species within colonies. At the sites studied, factors such as inherent differences in soil nutrient levels, sea-spray deposition, and soil texture appear to be of significance in determining the distribution of particular species.

No description available.