A theoretical model of flock size in migrating birds is developed. Although previous models of formation flight in birds show improved flight performance, they do not explain flock size variation across bird species or at different times of the year for a given bird species. This model captures some of the diversity in flock size observed in nature by incorporating energetic costs of flight and energy income from foraging. It turns out that within a myriad of possible flock sizes there - is one that is optimal for maximizing energetic efficiency (net energetic gain/energy expenditure) for a given maximum range speed, which minimizes flying cost per unit distance flown, and under certain migration conditions (i.e. flight distance and total time to complete the journey). Net energetic gain from foraging equals the rate of prey encountered times the time spent foraging. Energy expenditure from flying is determined from formation flight theory for a fixed wing aircraft. The benefit of formation flight, as derived from an approximation technique, is represented in close-form. This expression is a function of flock size and wing-tip spacing (WTS) and simplifies flight cost calculations. Under certain WTS, a good approximation to the induced drag for a member of a flock of size n is 1/nth of the induced drag of a single bird. In addition, optimum flight speed of a flock is (1/n)⅟₄ of the optimum flight speed of a single individual. The approach taken here allows the prediction of flock size in migrating birds. Model results are discussed in relation to observation of flock size under various migration conditions. If migration is constrained by hours of daylight, seasional variation in flock size is expected if the start time of the north and southward migration are asymmetrical with respect to the summer solstice (June 21). Under certain conditions, such as long non-stop migration, solo flight is an optimum migratory strategy. / Science, Faculty of / Zoology, Department of / Graduate

This study examined several aspects of the neural control of locomotion in birds. Initially, it was necessary to define an index of normal locomotor functions. This was accomplished for both flying and walking using electromyographic analysis of forelimb and hindlimb musculature to determine which muscles best define the flight and walking patterns respectively. Secondly, in chronic surviving birds, a series of subtotal spinal lesioning experiments were performed to determine which descending pathways were responsible for the initiation of hindlimb locomotion. Thirdly, results were recorded from brainstem electrical stimulation studies designed to determine the location of locomotor areas in the avian brainstem which effected the initiation and descending control of locomotion in these animals. Results indicated the iliotibialis cranialis (ITC) and flexor cruris lateralis (FCL) muscles best define the swing and stance phases of hindlimb locomotion, respectively. Muscles which best defined the elevator and depressor phases of flying were deltoideus major (DM) and pectoralis (Pect), respectively. Results of the low thoracic selective lesioning experiments support the hypothesis that the medullary reticulospinal pathway is necessary to the initiation and control of volitional hindlimb locomotion. Further, descending input to spinal cord pattern generators via the vestibulospinal pathways may play some adjunctive role or be necessary for the descending control of locomotion. Electrical stimulation of the brainstem in acute decerebrate birds elicited locomotor behaviours in both hindlimbs and forelimbs. Four areas, including; an area near the lateral /medial spiriform nucleus; nucleus et tractus descendens trigemini; and central nucleus of the medulla, pars ventralis and dorsalis; and the lateral reticular nucleus produced varying locomotor behaviours when stimulated. Acute dorsal cord transection did not affect the electrically stimulated behaviour, indicating that descending pathways from supraspinal centres which travel in the dorsal cord do not affect the descending control of locomotion. A strong parallel exists between the results of this study in two avian species and those found in the mammalian literature. / Science, Faculty of / Zoology, Department of / Graduate

Avian flight cannot fail to impress; from the huge migratory distances covered by albatrosses to the dexterity shown by a feeding hummingbird, the performance of birds in flight is remarkable. Until now research into free flight (i.e. not in a wind tunnel or other artificial environment) has been limited to observations from the ground. Here I use a collection of novel techniques, based on the use of onboard instrumentation carried by the bird, to explore if and how this performance might be underpinned by their flexible flight configuration. In the Introduction (chapter 1) to the thesis I investigate previous work into the stability and control of birds in flight. In chapter 2 I investigate a selection of manoeuvres seen commonly in flight, and describe the ways in which they exploit the flexible configuration of the eagle. Then (chapter 3), using an Inertial Measurement Unit (IMU) containing an integrated camera and Pilot-tube I measure the forces acting on the body of the bird in flight, the airspeed of the bird, and using custom-written software, I extract the configuration of the tail from the video. Using the measured configuration of the tail I estimate the lift generated by the tail according to a series of simple aerodynamic models. These are good predictors of the variation in the normal load factor acting on the bird. This suggests that the tail of the eagle is used primarily in soaring flight to balance the bird along the pitch axis. In chapter 4 I further investigate the configuration of the tail, I find that the spread and angle of attack of the tail covary, but that the twist of the tail is adjusted independently. In chapter 5 I explore one manoeuvre, the wing tuck, in more detail. With reference to a 'mean wing tuck' of the key variables I suggest that it is a response to a drop in wing loading, which suggests that it may be a response to atmospheric turbulence. I then investigate the frequency of wing tucking and our principal finding is that it is increased on days when the wind speed is greater, further suggesting that it is a response to atmospheric turbulence. Finally in the Discussion (chapter 6) I summarise the thesis. I also consider future avenues for research into the control and stability of avian flight and discuss some of the limitations of the methods used in this thesis.

No description available.

No description available.

This thesis is a journey that unfolds alongside the transformations of a river during springtime. Moods and movements captured by Ted Hughes in his poem Stump Pool in April inspire a series of explorations that set out to express the affective vectors of the river???s becoming through sculpture and architecture. The thesis is a manifestation of this search. Arranged as a narrative in five chapters, each offers an account of the emergence of the five works. The first three are a sculptural response to each stanza of the poem: Prometheus manifests the river???s phase-shift from ice to water, Sky Burial from water to steam and Icarus the passage of steam rising towards the sun. Prometheus??? torment, the tearing dispersal of the body during a funerary ritual and the ecstatic flight of Icarus are caught through three material and fire based experiments. Chapter four reflects on these works while investigating the conception and construction of the Bruder Klaus Chapel by the renowned Swiss architect Peter Zumthor. The fifth chapter moves the exploration from sculpture to architectural design deploying the lessons learned from the previous works. Forces of descent rather than ascent now inform the creation of a torrential void, A Lover???s Enclosure. The trajectory in each work and through the series is guided by what feels right, by the unpredictability of the material imagination, working by hand, and by forming and re-forming reoccurring themes as they reverberate and transform in a continuum of affective transformations.

No description available.