• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 10
  • 4
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 88
  • 17
  • 14
  • 8
  • 8
  • 7
  • 7
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Global ammonia emissions from seabird colonies

Riddick, Stuart January 2012 (has links)
Seabirds transport significant amounts of nitrogen from the ocean to the land in the form of excreta. The subsequent volatilization of nitrogen may result in significant emissions of atmospheric ammonia (NHs) in remote coastal systems. Blackall et aL, (2007) estimated global seabird NHa emissions to be 242 GgN year"1, however their emission estimate was not parameterised for all climate types and is based on old and potentially inaccurate historical population data. -- To update the global seabird NHs emission estimate, a contemporary seabird database of 261 million breeding seabird pairs was developed. This dataset was used in conjunction with a refined version of an existing seabird NHs model (GUANO) to estimate NHs emissions from seabirds in a range of climates. The estimate was further refined by using seabird habitat parameters that were validated through laboratory and field measurements. The field measurements, in various climate types, provide a more robust mechanism by which seabird emission factors could be validated for use in the global model A global seabird NHs emission estimate of 82 [37 - 127] Gg NHs year"1 is presented, with uncertainty as a result of variation in diet composition (± 23 %), non-breeder attendance (±13 %), ground temperature estimates (± 32 %) and seabird population estimates (± 36 %). -- Seabirds in the tropics are more significant emitters than previously thought, whilst emissions from polar regions were less significant than expected. The largest cafculated NHs emissions were on islands in the Southern Ocean and Pacific Ocean, with a maximum colony emission of 3.9 Gg NHs year"1 from the Sooty tern colony on Baker Island, Pacific Oceaa These NHs emissions are environmentally relevant, as they primarily occur as "hot-spots" in otherwise nutrient-free regions and may play a fundamental ecobgical and biogeochemical role in these ecosystems.
2

Studies of the infections of wild bird populations in north west England

Hughes, Laura Anne January 2008 (has links)
Little is known about the epidemiology of infection in wild birds. However, such infections can be zoonotic, transmitted to domestic livestock or both. Previous studies have resulted in conflicting evidence and views as to the role played by wild birds in the epidemiology of infectious diseases. This study aimed to determine the prevalence of a range of bacterial and viral pathogens in wild birds, over appropriate temporal and spatial scales, in order to begin to understand the (potential) role that birds play in the ecology of infectious diseases; in particular, to determine if wild birds act as sources and/or reservoirs of infection for human beings and/or domestic animals. This was achieved by carrying out a series of cross-sectional studies of wild bird populations in north-west England over a two year period. Samples collected from wild birds were examined for bacterial and viral agents including Campylobacter spp., verocytotoxigenic Escherichia coli, Salmonella spp., influenza A virus, avian paramyxovirus type-I, avian metapneumovirus, coronavirus and West Nile virus. Microorganisms were characterised using an array of microbiological and molecular techniques. Phylogenetic and epidemiological analyses were carried out to investigate host-pathogen ecology and evolution and to determine risk factors for the carriage of these agents by wild birds. Salmonellosis in wild passerines was found to be caused by a narrow range of possibly host-adapted S. Typhimurium strains, which were capable of invading and persisting in avian cells, susceptible to antimicrobials and contained a range of virulence genes, but lacked a gene that has been associated with some epidemic strains of S. Typhimurium in humans and livestock. It is suggested that S. Typhimurium infection in wild passerines is maintained within wild bird populations and it is unlikely that these strains represent a large zoonotic risk.
3

Nutritional aspects of breeding birds

Fidgett, Andrea January 2002 (has links)
No description available.
4

Ecology and conservation of large-bodied avian frugivores of Luzon, Philippines

Española, Carmela P. January 2013 (has links)
Avian frugivores across Southeast Asia, and in the Philippines in particular, are seriously threatened owing to massive loss of habitat and direct exploitation through hunting and the pet trade. Their declines may have dire consequences for wider ecological processes as many frugivores are also seed dispersers. Conservation programmes in the Philippines are crippled by a lack of knowledge on the status, abundance and ecology of frugivores which extend to other endemic species in the country. This PhD identified factors that influenced frugivore community composition as well as drivers of frugivore distribution across Luzon, the largest island in the Philippines. It also developed cost-effective methods for gathering baseline ecological data to inform conservation measures for frugivores and other little-known species over large geographical areas. This included a way of correcting for the bias caused by non-random transect placement in a study site which is often the case during bird surveys in the tropics. Twenty-five species of pigeons, parrots and hornbills were surveyed using distance sampling along nearly 500 km of line transects at 14 sites across the island of Luzon. I documented surprisingly few reliable disappearances of frugivores from individual forest patches – in fact this and other fieldwork since 2000 has increased the known extent of occurrence of several species. However, green racquet-tail Prioniturus luconensis may have suffered a real range contraction. More alarming was the absence of large parrots from most sites with apparently intact habitat surveyed. Even where present, large parrots exhibited lower densities than related species in similar habitat in Southeast Asia. For six species, including four of six parrots, the largest estimates of population in any reserve in Luzon numbered < 1000 individuals, and nearly one-third of all iii populations in reserves were < 100. At minimum viable population (MVPs) of 500, frugivore communities in all but 2–3 of the largest reserves are not expected to remain intact. Although seed dispersers may fare better than seed predators (large parrots), a major collapse of frugivore communities may occur across Luzon, with serious implications for ecosystem functioning. The Philippines comprise islands of different origins, climate and habitat, a situation which is expected to produce a biogeographically complex set of animal and plant communities, which themselves are influenced by anthropogenic actions. I explored similarities between frugivore communities across 24 sites in Luzon using non-metric multidimensional scaling and attempted to explain site differences in terms of a series of geographical, habitat, and disturbance predictors using Mantel tests. In both analyses using species presence/absence and densities, sites/species did not seem to ordinate simply according to region. Consistent outliers included three sites in West Luzon and two in Central Luzon, and, in terms of species, several large rare parrots and pigeons. The strongest correlates of site dissimilarity were differences in altitude and several human disturbance measures, including path width, canopy closure and a ‘human impact index’ (reflecting human pressures and forest management). While Luzon’s frugivore communities have been no doubt shaped by natural biogeographical processes, their effects have been largely obscured by anthropogenic environmental degradation. There is an urgent need to understand better the drivers of frugivore species distribution in order to develop appropriate conservation management strategies. To identify precise habitat associations of 18 avian frugivores, the presence/absence of each species along 400 m long segments of 213 transects was examined in relation to vegetation structure and composition, measured at 1227 plots, using generalised linear mixed models (the 24 sites were entered as a random factor). Individual frugivore species showed unique patterns of iv association with habitat variables but five species were high-altitude specialists while six preferred lowland sites. Another six species strongly preferred primary forest while one thrives in disturbed forest with the attendant increase in food availability. I then ran generalised additive mixed models (GAMMs) to identify any non-linearities in responses of species to habitat features. Relationships with habitat variables were on the whole simple linear or quadratic for the majority of species, suggesting that there were gains to be had in improving habitat right along the disturbance gradient. Precise and accurate estimates of wildlife population density and sizes are essential to evidence effective conservation programmes. Line transect distance sampling is a robust method in that variability in detectability due to distance from the transect line, but many conservation studies cannot, by necessity, be based on random transect placement, but instead use transects along existing trails. This study estimates the bias in abundance estimates due to non-random placement of transects along hunter trails (path width <100cm) and access roads (path width >100cm) as compared with random paths (especially cut transects). Path types were similar in altitude, but differed in terms of tree girths, slope, canopy covers, and presence of crops. Hunter trails yielded lowest densities and encounter rates for nine of 12 species and lowest effective strip width for seven of 12 species. Highest densities and encounter rates were along random paths for seven of 12 species. Differences in density across trail types were driven by differences in encounter rates rather than differences in detectability. Density estimates calculated from surveys which used non-random transects should be upwardly corrected by on average 90% (18-187%). In fragmented forests where random placement of transects is not always possible, this method of correction will allow species density estimates from sampling along hunter trails and access roads to be adjusted. v Top on the list of research and conservation priorities arising from this PhD would be to map the remaining populations of the Luzon-endemic Green Racquet-tail, Luzon Racquet-tail and Flame-breasted Fruit-dove and to formulate conservation intervention measures for these threatened/near-threatened species taking into account habitat preferences and threats to the species. Forest and reserve management programmes and policies in the Philippines and elsewhere in the tropics would greatly benefit from empirical data on species occurrence and accurate estimates of population abundance using methods described in the study. Sound ecological research by local biologists/ecologists must be encouraged to further our understanding of species requirements, species tolerance to disturbance, and viability of populations, especially of the many unique and/or threatened species in the Philippines and the wider SE Asia region.
5

Spatial cognition in three dimensions

Flores Abreu, Ileana Nuri January 2013 (has links)
To date, most studies of spatial learning have been conducted in the horizontal plane, with few addressing the vertical dimension. I aimed to investigate learning of 3-D locations by wild, free-living hummingbirds and compare them with rats. In my first experiment, I found that hummingbirds can encode a 3-D rewarded location after a single visit. Using a one-dimensional array, I then found that the birds more readily learned a location in a horizontal than in a vertical linear array. However, the ease of learning was a product not only of the orientation of the array but also of its spacing scale. By the end of training, hummingbirds visited the central rewarded flower and the two adjacent flowers more than they visited the distal flowers for all arrays. However, when the array was horizontal and the flowers spaced 30 cm apart, they learned the absolute location of the rewarded flower. In a diagonal array birds learned the 2-D reward location but they chose at random when tested on a vertically or horizontally oriented array. However, when birds trained in the diagonal array were tested on a 180° rotated diagonal array they chose the flower with the same horizontal component as the rewarded flower rather than with the flower with the same vertical component. Finally in order to compare the spatial learning of animals that move in volumes with those who move in two dimensions I trained hummingbirds and rats to a rewarded location in a cubic maze. Although both hummingbirds and rats learned a 3-D location within a cubic maze, hummingbirds appeared to learn the rewarded location as a 3-D coordinate while rats seemed to learn the vertical and horizontal component of the 3-D location independently. In addition, hummingbirds were more accurate in the vertical and rats in the horizontal, which is consistent with their type of locomotion. More experiments in volumetric, terrestrial and climbing animals are needed in order to determine whether the contrasting search strategies and learning accuracies constitute adaptations to particular spatial niches.
6

Characterisation and ecological effects of garden bird feeding

Orros, Melanie January 2013 (has links)
Garden bird feeding is amongst the most widespread of human-wildlife interactions worldwide, particularly in urban areas. Despite the evident scale of energy input and subsequent likely ecosystem perturbation however, surprisingly little research has investigated this activity. Most previous work has focussed on direct influences on provisioned birds and has taken place outside gardens. Effects seen in other locations and under experimental feeding regimes may differ in nature and extent from those within the highly anthropogenically modified and diverse habitats of gardens and under householders' usual provisioning patterns. My research focussed on garden bird feeding in a large UK urban area centred around the town of Reading. Questionnaires revealed that over half of households feed birds, predominantly year-round. A longitudinal study indicated that a median of 628 kilocalories/garden/day is given. UK-wide this could support c. 200 million individuals of an average garden-feeding bird (based on 10 common species) assuming 100% uptake. Reading is unusual amongst UK urban areas in that reintroduced red kites (Milvus milvus) are now common day-time visitors. The combined results of several studies suggested that garden feeding is key to this urban presence. Surveys of kite feeders indicated that median provisioning levels could support c. 160-355 kites/day across the Reading urban area and further that most feeding meets recommended guidelines. Garden bird feeding can also indirectly influence co-existing taxa. Comparisons of aphid colonies exposed to and protected from birds in both feeding and non-feeding gardens found significant reductions in size and survival time of exposed relative to protected colonies only in feeding gardens. Further work revealed reduced numbers of Carabidae around bird feeders compared with control areas under householders' usual provisioning patterns. These depletory effects are attributed to increased avian predation around bird feeders. Overall, my research demonstrates that a common domestic activity has a diverse range of influences both on targeted species and indirectly on others. Further research is required to investigate the significance of these worldwide.
7

Exploring the impact of common buzzard Buteo buteo predation on red grouse Lagopus lagopus scotica

Francksen, Richard Michael January 2016 (has links)
The relationship between raptors and red grouse Lagopus Lagopus scotica is one of the most topical and contentious wildlife management issues in Britain. The common buzzard Buteo buteo is a generalist raptor which has increased in population and range in Britain during the last 40 years, which in most areas represents a recovery following historical declines. Increasingly, this has reignited conflict with managers of gamebirds concerned about the impact of buzzard predation. Whilst the impact of buzzards on reared pheasants Phasianus colchicus has previously been assessed, the impact of buzzards on red grouse has not been investigated. I aim to address this knowledge gap by providing an insight into the predator-prey relationship between buzzards and red grouse. I have explored the diet, foraging patterns and responses to changing prey abundances of buzzards on a moorland site managed for red grouse in south-west Scotland. First, I investigated the biases associated with methods of assessing raptor diet. I demonstrated that methodological biases exist and that these can vary over time in relation to natural temporal variations in raptor diet composition. I then investigated functional and numerical responses of buzzards to annual changes in prey abundance. Following declines in vole abundance, buzzards selected a wider range of prey, but consumption of red grouse did not increase, and there was no evidence of a numerical response. Results suggested that buzzard predation of red grouse may be incidental in nature, whereby high vole abundances encouraged buzzards to hunt in red grouse habitats. Next, I explored buzzard foraging patterns in relation to prey and habitat. Buzzard foraging intensity varied in line with annual variations in vole abundance, and buzzards hunted in areas with more red grouse during the winter. Buzzards avoided heather dominated areas in years when vole abundance was low, but not when vole abundances were high. Results again suggested that incidental buzzard predation of red grouse could increase when vole abundances are high. However, I found no evidence that variations in buzzard foraging intensity influenced grouse mortality indices. iii I then described buzzard diet during the winter with the aid of remote tracking methods. Buzzard diet was primarily composed of small mammals, and red grouse were less likely to feature in the diet of buzzards roosting in grassy areas. Next, I produced estimates of the potential removal of grouse by buzzards using bioenergetics modelling. The results suggested that whilst the removal of grouse by an individual buzzard is likely to be small, the total number of grouse removed could be considerable if buzzard populations are high and predation of grouse is additive to other causes of mortality. Finally, key results are discussed and placed in a wider context of upland and gamebird management in Britain. Recommendations are made for future study to improve our understanding of these systems, and for testing possible mitigation and management techniques. This study could have wider implications for the management of economically important or threatened species, alongside recovering populations of protected raptors, and may provide a useful framework for studying similar systems elsewhere.
8

Investment patterns and kinship cues in a cooperatively breeding bird

Khwaja, Nyil January 2017 (has links)
In cooperatively breeding species, ‘helpers’ provide care for other individuals’ offspring. Research into cooperative breeding, which initially asked the deceptively simple question ‘why?’, has continued to provide insights in behavioural ecology thanks to the opportunities for adaptation and coevolution that are generated in these unusual societies. I explore some of these potential adaptations in detail, mainly through studying a population of riflemen Acanthisitta chloris, which are passerine birds endemic to New Zealand. Previous work showed that riflemen are kin-based, facultative cooperative breeders. Most help is provided by adult birds, who have dispersed from their natal territory, but commute short distances to provision at the nests of relatives. Help is associated with enhanced recruitment of related offspring, and thus considered likely to confer indirect fitness benefits. These conclusions are substantiated by my results. Provisioning by helpers is a special case of parental investment, and in Chapter 2 I characterise investment by rifleman carers. I find that sealed-bid and conditional cooperation models are inappropriate to describe investment in riflemen, and discuss possible reasons for this. I also demonstrate the validity of provisioning rate as a measure of food delivery in riflemen. In the following two chapters I test the hypothesis that helping drives adaptive sex allocation in cooperative breeders, first using data from riflemen, and then across 26 bird species. Surprisingly, the hypothesis is not supported in either case. In chapters 5 and 6 I consider how riflemen recognise their relatives in order to direct help to them. I identify candidate vocal and chemical kinship cues and test the responses of provisioning riflemen to olfactory manipulations and call playback. My findings have implications for measuring parental investment in birds; show interesting discrepancies with evolutionary theory, and illustrate opportunities and challenges in sensory ecology. These themes are discussed in the final chapter.
9

Assessing the potential impacts of anthropogenic disturbance on seabirds : a case study from Alderney

Warwick-Evans, V. C. January 2016 (has links)
Seabirds are threatened by multiple anthropogenic pressures in the marine environment. These pressures may be short- or long- term and impacts may be either direct or indirect and affect reproduction or survival. Marine Renewable Energy Installations (MREIs) provide a relevant, and spatially explicit, example of such pressures. However, there is currently very little empirical evidence as to how MREIs will impact seabirds. Studies have shown that potential impacts are likely to be species and device specific, temporary or long term, and both positive and negative. Current approaches to predict and assess these impacts from MREIs rely on understanding the species- specific risk of devices (e.g. by making predictions based on the ecology of the seabird), the occurrence of individual species at-sea (e.g. from boat-based surveys), and demographic studies of breeding populations (e.g. through long-term ringing studies). However, these approaches are limited in their ability to detect changes in the distribution of seabirds at-sea and at breeding colonies. They may omit the impacts on non-breeding birds, and overlook the cumulative impacts of multiple pressures on specific populations when predicting potential impacts. Alderney in the English Channel hosts internationally and nationally important seabird colonies, in addition to providing a suitable environment for the installation of tidal turbines. Additionally, the home range area of the colony of Northern gannets Morus bassanus breeding just offshore of Alderney overlaps with nine sites proposed for the development of MREIs, thus Alderney provides an ideal site for this type of study. This thesis explores simple approaches to predict and assess the impacts of proposed MREIs on seabirds, and demonstrates how the large amount of existing seabird tracking data can be used to predict the colony specific impacts of spatial change on seabirds. These approaches are developed at our Alderney study site but are broadly applicable elsewhere. Overall our results suggest that the MREIs proposed for development around Alderney and the English Channel are unlikely to cause population level impacts to the seabirds breeding on, and around, Alderney. With ever increasing human pressures on the marine environment it is vital that we identify robust approaches with which to predict and monitor the impacts of these pressures. This thesis provides simple, robust and cost-effective approaches to predict and assess the potential impacts of spatial change on seabirds, and could be easily adapted for other sites, and for alternative types of spatial change.
10

The innervation of the air passages of the avian lung and observations on afferent vagal pathways concerned in the regulation of breathing

McLelland, John January 1970 (has links)
No description available.

Page generated in 0.0225 seconds