There is often a reciprocal relationship between predators and their dominant prey. This results in continuous co-evolution, where the prey selects more efficient ways to avoid predation and the predator selects more efficient ways of catching prey. The aim of this study was to determine if aerial predators (raptors) influence diurnal activity patterns of their prey (mice). Sampling of both raptors and mice was done simultaneously during autumn, winter and spring at two different study sites in three different habitats on South Africa's arid west coast. Sixty PVC mouse traps were checked every half hour throughout all daylight hours and raptors were observed using scan sampling every two minutes. A total of 1228 rodents were trapped consisting mainly of the diurnal mouse, Rhabodmys pumilio and a total of 197 hours was spent observing hunting behaviour of four raptor species: Black and African Marsh Harriers (Circus maurus and C. ranivorus), Black-shouldered Kite (Elanus caeruleus) and Rock Kestrel (Falco rupicolus). All birds hunt rodents on a regular basis and all were beginning to breed towards the end of my study. Results showed significantly higher small mammal activity during winter and in habitats with dense vegetation. Diurnal small mammal activity peaks appeared to shift randomly between sites, habitats and seasons, thereby avoiding predation through unpredictability of activity. Small mammal activity patterns deliberately avoided peak foraging times of raptors during winter at the Pelican site; however this relationship was not linked to any climatic variables to explain how mice avoid high predation periods. Raptors selected peak foraging times dming periods of high small mammal activity at the Dune site during winter; however wind speed and cloud cover were correlated with both raptor foraging and small mammal activity, thereby influencing the relationship between the predator and the prey. In conclusion, no reoccurring diurnal peaks in small mammal activity were seen across the three seasons and this may have been an anti-predation strategy, because predators would find it more difficult to predict high prey activity. However the raptors it seemed were selecting periods of high mice activity at one site when weather conditions allowed.

The study of the ecological life history of the Cape Bulbul Pycnonotus capensis was carried out in 20 hectares of coastal dune forest near Port Elizabeth, South Africa. Results from four years 1959 to 1962 are given in detail and only the number of breeding pairs present in 1958 have been used from observations that year. The Cape Bulbul is one of three closely related species of a predominantly tropical family. Intra specific breeding is rare and occurs only where man has altered the habitat. Distribution has altered slightly in 150 years where colonisation has occurred. Several conditions may influence distribution, the species is mainly limited to within winter or all year round zones of rainfall. Population of breeding pairs varies from nine to 19 pairs. It is the commonest species in the area. There is a 25% annual adult mortality with life expectancy of an adult about three years. Competition for food is negligible. Predators concern mainly the nesting cycle. Clutch size which is two or three is not regulated by food supply or population changes. Main changes are due to emigration and immigration which is apparently influenced by density-independent factors.

Includes bibliographies. / The waterbird populations of the Berg River estuary, South Africa, were studied from September 1987 to April 1989. The main objectives of the study were to assess the importance of the estuary for Palearctic-breeding migratory waders and to identify the factors affecting their distribution, abundance and behavioural patterns. The findings were related to the dispersion patterns of waders on the east Atlantic seaboard, and their significance was evaluated in the light of predictions of current models for the migratory behaviour of shorebirds. Controversy over the Winter competition model is discussed. The intertidal mudflats (144 ha) at the Berg River estuary support an exceptionally high density of migratory shorebirds during the austral summer. The high density of birds results in a high predation pressure. Although the rate of prey removal by birds is one of the highest recorded in the east Atlantic, it represents only 17% of the annual production of invertebrates. A bird-exclusion experiment confirmed that birds have little impact on their prey populations. Although the energy balance for the majority of species was apparently negative for much of the austral summer, the energy deficits measured in the field were less than those recorded in north temperate estuaries. The highest predation pressure by birds coincided with the period of highest production of the most important invertebrate prey. Because of low prey diversity in the estuary, there was considerable overlap in the prey species taken by different bird species. The preferred prey of most species were nereid worms. Within this prey class there were clear differences in the size classes of worms eaten by different birds. The distribution of birds on the estuary was related to both biotic and abiotic factors. The observed patterns of partitioning of both food and space resources was attributed to the superabundance of prey and to interspecific differences in foraging techniques unrelated to competition. The spatial redistribution of birds within the estuary during the first four months after their arrival from the breeding grounds was related to changes in feeding conditions on their preferred foraging sites, rather than density-dependent factors mediated by competition. I propose that a combination of high prey abundance and production, coupled with an apparently low level of competition, makes the Berg River an attractive nonbreeding site for migrant waders. Their relatively sound energy budgets and the benign climate may enhance nonbreeding survivorship sufficiently to offset any additional risks incurred in long-distance migration.

Bibliography: pages 154-162. / The aims of the present study are threefold. Firstly, the coexistence of the two closely related, normally allopatric, albatross species is investigated in their zone of overlap where interspecific competition for food resources and nesting space is likely to be most acute. Secondly, the genetic isolation of the two species is investigated, as co-existence implies increased interspecific social interaction with associated increased possibilities of hybridization. Thirdly, the two species' possible evolutionary histories are examined in relation to their ecologies. Logistical constraints prevented study of fusca and palpebrata on the feeding grounds, i.e. at sea, and feeding could be studied only indirectly.

The dissertation comprises a general introduction, five chapters and a summary-synthesis which is designed to link the chapters into a cohesive account. Chapter 1 deals with the avian population of a southwestern Cape sandy shore and compares this population with those of sandy beaches in the eastern Cape and Natal. The abundance of birds and the estimated energy requirements of the avian populations in these three geographical areas increase during the austral summer, due to an influx of migrants from the northern hemisphere. The proportion of migrants to residents varies geographically, being greater in the southwestern Cape and Natal than in the eastern Cape. Chapter 2 summarizes information on the systematics, global distribution and morphology of two small shorebirds, the White-fronted Sandplover Charadrius marginatus and the Sanderling Calidris alba, which are identified in Chapter l as being dominant components of the southwestern Cape sandy shore avian population. Chapter 3 reports on the spatial and temporal use of the intertidal habitat by foraging White-fronted Sandplovers ·and Sanderlings. Interactions between these two species are discussed in the light of competition theory. The foraging ecology of the Sanderling and White-fronted Sandplover at Ouskip differed strikingly. Although both species exhibited a tidal cycle in foraging activities, rather than a diurnal cycle, White-fronted Sandplovers tended to feed during the latter half (i.e. mid to high tide), whereas Sanderlings fed during the first half (i.e. low to mid tide) of the tidal cycle. Both species' foraging activity also varied spatially and seasonally. White-fronted Sandplovers fed primarily in drier microhabitats above high tide level, and Sanderlings in wetter microhabitats near the water's edge. In Chapter 4, the size and structure of Sanderling flocks are described. The frequency distribution of flock sizes of wintering Sanderlings foraging on the sandy beach at Ouskip was bimodal, with a peak at small flock sizes and another at large flock sizes. It is hypothesized that large groups of Sanderlings consist of individuals searching for subterranean prey, and that small groups consist of subsets of these larger groups which have located food patches. Chapter 5 is an analysis of breeding periodicity in White-fronted Sandplovers in southern Africa, and focuses on the relationships between geographical and year-toyear variation in breeding activity and rainfall patterns, food availability and the possible effects of competition with migrant shorebirds. This species exhibits significant geographical variation in breeding season, and significant year-to-year variation within an area which has winter (May - August) rainfall. There was no year-to-year variation in breeding season within an area with summer (November - February) rainfall.

Elemental contaminants aggregate in the environment due to human activity and can induce detrimental physiological effects within organisms. Birds exhibit exceptional susceptibility to many pollutants and are popular biomonitoring agents throughout the world. Birds of prey are of special interest due to their substantial biomagnification potential. Lethal sampling of internal organs yields accurate contaminant measurements, but recent sampling trends are endeavoring towards non-destructive sampling such as feathers. This methodological shift stems from researchers' preference for less-regulated samples, enhanced animal welfare, and broadening the possible collaborative audience with simpler protocols. Unfortunately, investigations of feathers have shown that their accuracy is capricious due to a wide variation of analysis results, which may be a result of external deposition or the broad temporal range of feather contaminant assimilation. The Red-shouldered Hawk, Buteo lineatus, is a diurnal terrestrial generalist found along the Atlantic Flyway. This study investigated the blood feather, which is an actively growing feather, as an alternative non-lethal sample type for quantifying elemental contaminants in B. lineatus. Sex and age class influences were also investigated. Blood feather, feather, and kidney tissues were collected from 50 B. lineatus and livers from 42 of the same B. lineatus. Samples were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for aluminum (Al), phosphorous (P), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), gadolinium (Gd), and lead (Pb). Blood feathers, when compared to feathers, had stronger correlations with internal organs for As and Pb. There were significant sex differences in liver tissues for Co, Cu, Zn, Cd, and Ni, where males generally contained elevated concentrations compared to females. The age class of the bird influenced the amount of metal accumulated in their organs. Prefledglings and fledglings had significantly lower concentrations compared to either immature and mature birds for Al, Cd, and Pb in liver tissues as well as Al, Mn, Fe, As, Cd, and Pb in kidney tissues. None of the B. lineatus samples exceeded previously reported sublethal levels.

Birds are often used as indicators for biodiversity and ecosystem health. While birds have been monitored in other parts of the Indian River Lagoon (IRL), there has been little research on birds in Mosquito Lagoon (ML, the northernmost portion of the IRL). This thesis first examines the abundance and diversity of birds in ML by using two years of photographic observations to assess seasonal variations and the use of various habitat features by specific bird taxa. Abundance and species richness were highest in winter, while evenness and Simpson's diversity were highest in summer. Moreover, natural and artificial habitat features were differentially utilized by specific bird taxa. A second objective was to use monthly bird surveys for three years to assess the utilization of live, restored, and dead oyster reefs by birds and to determine how oyster reef restoration impacts the bird community in ML. Infaunal abundance was also monitored in the reef sediments, as infauna serve as prey for birds. Results indicated that while restored reefs had relatively low bird abundances, they had similar proportions of foraging birds and similar bird assemblages as live reefs. By 6 months post-restoration, infaunal abundances on restored reefs became similar to live reefs, indicating similarities in prey availability. Another goal was to explore the selection of certain dead reefs by nesting Least terns and American oystercatchers. Reefs on which nesting activity had previously been observed were characterized and compared to reefs where nesting was not previously observed. Nesting sites had taller mangroves, steeper slopes, higher elevations, more vegetative cover, and less live oyster cover than non-nesting sites. Overall, results indicate that live, restored, and dead reefs are all being utilized by birds in ML, and that a mosaic of reef types may be best for providing foraging, loafing, and nesting habitat for birds.

1. Many species of bird breeding in Britain have declined in recent decades. However, only in the farmland ecosystem are the majority of species, primarily seed-eating passerines, declining. Similar declines in these species are also occurring elsewhere in Europe and North America. This thesis aims to model the effects of habitat change on population size ofthese species through an understanding of their behaviour. 2. A wide range of factors, primarily relating to the intensification of agricultural management, have been implicated in these declines, and these are reviewed in detail. There is little evidence for consistent impacts on the breeding biology, but considerable circumstantial evidence that declines in winter food supply have been a major cause of the declines. 3. Three species of seed-eating passerine are studied in detail, skylark Alauda arvensis, yellowhammer Emberiza citrinelia and com bunting Miliaria calandra. In winter, yellowhammers and com buntings used stubble fields exclusively; skylarks much preferred stubble fields. All avoided winter cereal fields. This is related to seed density, stubble fields held virtually all the cereal grain found in the soil and many more weed seeds than winter cereal fields. 4. The functional responses of skylarks, yellowhammers and com buntings are described. Seed availability plays an important role in determining intake rate, with seeds buried beneath the surface harder to obtain, particularly for yellowhammers. Seed availability has more general implications for the nature of functional responses. 5. Bird numbers were related to seed density, the aggregative response. The scale at which aggregative responses were observed varied between species. The availability of seeds in the soil column affected the birds use of fields, with the number of seeds on the surface important. The location of hedgerows was also important, yellowhammers and com buntings preferred to forage close to them, skylarks did not. 6. The general effects of overwinter mortality on population size are modelled and the effects of two causes of winter mortality, starvation and predation are analysed. Individuals traded-off these two risks which had an interactive effect on mortality. Density-dependence in the breeding season interacts with winter mortality to set population size. 7. The results presented in this thesis are used to model the effects of habitat changes on populations of seed-eating birds. The predicted population, on the basis of winter food supply, was close to the current actual population size. These models are used to assess the effectiveness of different management options, with unharvested conservation headlands being best for species such as the yellowhammer and tree sparrow Passer montanus, while set-aside is best for species such as the skylark.

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