One of the most striking things about many animals is that they can be defined by the ways in which they move. Moving costs metabolic energy and is a significant contributor to the daily energy balance of organisms and therefore fitness. Balancing energy needs is critically important to species inhabiting areas of limited resources. The metabolic cost of locomotion is influenced by physiological, morphological and behavioural factors that vary across species. The influence of these factors within species is less well understood. The objective of my PhD is to elucidate the potential for variation in locomotor performance, in particular the energy consumed and the biomechanics of locomotion within a species, in response to differences in season, sex, age and the nature of the terrain. The Svalbard ptarmigan (Lagopus muta hyperborea) is the only year-round avian resident of the Arctic archipelago of Svalbard. Svalbard is characterized by extreme photoperiodic and climatic conditions, with 24 hours of daylight in summer and continuous darkness in winter, when ice makes food unpredictable. As a result, ptarmigan annually gain significant fat stores, as much as doubling their body mass in winter. The consequences of such large gains in mass upon the metabolic cost and biomechanics of terrestrial locomotion are yet to be quantified. The Svalbard ptarmigan represents a unique opportunity to gain insight into avian adaptations.Using respirometry, I present evidence that winter birds are able to carry their fat stores at no metabolic cost. Using kinematic and force plate data, I show that acquiring fat results in reduced locomotor performance in terms of speed and take-off ability. As well as exhibiting phenotypic variation, male and female Svalbard ptarmigan are behaviourally very different. I present evidence that these behavioural differences are reflected in the metabolic cost of locomotion. In particular, males are both more efficient and faster than female birds during both summer and winter. I suggest that this results from sexual selection upon male locomotor performance. Furthermore, I present data demonstrating that sub-adult males experiencing their first winter possess the same metabolic and speed capabilities of adults. These data may indicate that selection for improved male locomotor performance may act upon sub-adult birds. Regardless of season, age or sex, Svalbard ptarmigan must locomote on a predominantly sloping terrain. The influence of inclines upon the metabolic cost of locomotion in birds is poorly understood. I provide evidence that at the same degree of incline, the cost of lifting 1 kg by 1 vertical metre is similar regardless of season and is therefore dictated by increased positive work. However, this cost varies according to the degree of incline and may be influenced by gait.The principal findings of the 5 first author papers presented are that behavioural, physiological and morphological variation within a species can have significant impacts upon the metabolic cost of locomotion and other aspects of locomotor performance. The potential for intraspecific differences should therefore be taken into account in future research regarding the patterns of energy expenditure in animals.

This thesis investigates how collective decisions in bird flocks arise from simple rules, the factors that give some birds more influence over a flock's direction, and how travelling as a flock affects spatial learning. I used GPS loggers to track pigeons homing alone and in flocks, and applied mathematical modelling to explore the mechanisms underlying group decisions. Across several experiments, the key results were as follows: Flying home with a more experienced individual not only gave a pigeon an immediate advantage in terms of taking a more direct route, but the followers also learned homing routes just as accurately as pigeons flying alone. This shows that using social cues did not interfere with learning about the landscape during a series of paired flights. Pigeons that were faster during solo homing flights also tended to fly at the front of flocks, where they had more influence over the direction taken. Analysis of momentary interactions during paired flights and simulations of pair trajectories support the conclusion that speed increases the likelihood of leading. A pigeon's solo homing efficiency before flock flights did not correlate with leadership in flocks of ten, but leaders did have more efficient solo tracks when tested after a series of flock flights. A possible explanation is that leaders attended more to the landscape and therefore learned faster. Flocks took straighter routes than pigeons flying alone, as would be expected if they effectively pooled information. In addition, pigeons responded more strongly to the direction of several neighbours, during flock flights, than to a single neighbour during paired flights. This behaviour makes sense adaptively because social information will be more reliable when following several conspecifics compared to one. Through a combination of high-resolution tracking and mathematical modelling, this thesis sheds light on the mechanisms of flocking and its navigational consequences.

Louping ill virus (LIV) is a tick borne disease that causes mortality in red grouse, an economically important game bird of British uplands. The aim of this thesis is to extend previously published models of LIV , to consider the potential impact of different management strategies. In addition a new route of infection and the seasonal biology of both grouse and ticks will be explored. Grouse chicks are known to eat ticks as part of their diet in the first three weeks of life which may contribute to virus persistence if chicks consume infected ticks. This novel route of infection is incorporated in to the model which predicts that ingestion increases the range of host densities for which the virus is able to persist. The ingestion of ticks by grouse also reduces the tick population so that for low host densities the ingestion of ticks by grouse reduces the tick population so virus cannot persist. The model is adapted to take account of the seasonal biology of grouse and ticks. Although the temporal predictions of the seasonal models show some differences the addition of seasonality does not alter the model predictions of when LIV is likely to persist at different grouse and deer densities. Consequently seasonality is felt to be unimportant when considering management strategies. The treatment of sheep with acaricide in an attempt to reduce the tick population on a grouse moor is currently being trialled in Scotland. We use a model to predict the likely effect of this strategy at different deer densities. The number of ticks found attached to sheep varies so we consider the effect of tick attachment rates as well as acaricide efficacy. Although we predict that acaricide treated sheep can reduce the tick population and therefore LIV in grouse in some circumstances the treatment is less effective in the presence of deer. Consequently we use a model to make theoretical predictions of the effectiveness of acaricide treated deer as a control strategy for reducing LIV in red grouse. The effect of culling deer on LIV in grouse is also modelled and contrasted with the effect of acaricide use. It is predicted that acaricide treatment of deer could be highly effective, particularly if the deer density is first reduced by culling. Finally we considered the direct treatment of red grouse with acaricide. Female grouse can be given an acaricidal leg band which protects her directly and indirectly protects her chicks as they acquire some acaricide whilst brooding. Trials have suggested this can reduce tick burdens for individuals. We use the model to determine the potential effect that treating individual broods may have on the whole grouse population. The model predictions suggest that unless acaricide efficacy on chicks is high and long lasting treating individual broods is unlikely to reduce LIV in the whole population but will still provide some benefit for the individuals. The effectiveness of treatment is reduced by higher deer densities. The success of the management strategies considered in this thesis appear to be restricted by the presence of deer. It may therefore be that a combination of treatments including the treatment of deer may be of the greatest benefit to the grouse population.

As planted forests mature and are clearfelled in patches, second rotation tree crops (restocks) become available to black grouse, a species of conservation concern in the UK. Currently, only a limited amount is known about the resources provided by this habitat to black grouse and their broods. The aims of this study therefore, were to investigate the recovery of field-layer vegetation and the invertebrate population from restock through to canopy closure of planted trees, assess the duration of habitat availability and food resources to black grouse, and understand how forest management could improve provision. Changes to the abundance of predators resulting from habitat management were also considered. The comparative habitat quality of restocks was assessed in a wider landscape context. Field-layer vegetation in 72 restocks in two afforested areas in the north-east and the south-west of the Scottish Highlands was surveyed. On average, only 60% of ground in restocks was re-planted with second rotation trees, with the remainder left unplanted. Initial vegetation recovery was generally impeded by timber harvest residues (mainly brash), which comprised up to 50% of total ground cover two years after restock. Increased cover of heather Calluna vulgaris, often an important component of black grouse habitat, and decreased brash cover were recorded in areas of restocks where first-rotation timber was removed by cable-winch (compared with harvester and forwarder removal) and in planted areas (compared with areas left unplanted). Bilberry Vaccinium myrtillus and cotton grass Eriophorum spp. occurrence was recorded infrequently irrespective of restock age or management. Heather generally dominated the field-layer six years after restock, reaching a height and density reported to be suitable for black grouse nesting and brood cover in other studies. The onset of tree canopy closure as early as eight years suggests that suitable black grouse habitat availability in restocks is likely to be severely limited in duration. Brash removal, or break-up and re-distribution of the brash layer, positively affected the recovery of field-layer vegetation species potentially of use to black grouse. Extending the fallow period prior to restock resulted in an extended period of suitable habitat available to black grouse prior to canopy closure. However, habitat created by extending the fallow period also attracted a higher number of mammalian predators of black grouse. In the longer term, areas of restocks left unplanted should provide a valuable open-ground resource after canopy closure of the planted crop, although results suggest that management to prevent encroachment of naturally regenerating non-native trees is likely to be necessary. Invertebrate taxa selected by chicks in previous black grouse studies were available in all ages of restock studied. Taxa abundance differed as restocks aged and field-layer vegetation developed, although contrasting habitat preferences of taxa meant that each was affected differently by restock management. No single forest management method positively increased abundance of all taxa. Abundance of Lepidoptera larvae, a key food item for black grouse chicks, was positively related to dwarf shrub cover. An extended fallow period prior to restock should prolong increased larvae availability to chicks. Provision of preferred field-layer vegetation habitat and invertebrate abundance in restocks was comparable to habitat surrounding leks - areas likely to be occupied and utilised by black grouse. Restocks had a comparatively low occurrence of key plant species, including bilberry Vaccinium myrtillus and cotton grass Eriophorum spp. Cover of the dwarf shrub bog myrtle Myrica gale, positively associated with Lepidoptera larvae abundance in habitat surrounding leks, was absent from restocks. The abundance of other invertebrate taxa considered was similar between leks and restocks. Study findings are discussed with reference to black grouse conservation and commercial forestry systems in Europe. Management recommendations to improve habitat for black grouse in second rotation planted forests in Britain are provided.