No description available.

No description available.

No description available.

This study investigates the influence of autoecological factors both on the spatial pattern of abundance, and on the demographic fragmentation, of the breeding population of the Rook (Corvus frugilegus L.) in Scotland. Two scales of analysis are considered, namely the regional scale (Scotland) and the landscape scale (Ythan catchment area). The study focuses on the investigation of how land use factors interact with other environmental variables. Patterns of association of the breeding density with land cover, climatic and soil factors are searched for and statistically examined. Soil factors, in particular, have been investigated in detail for the first time, because of their potential to influence the population of earthworms, the main prey for the Rook during the breeding season. A geostatistical simulation is used to address the problem of data spatial autocorrelation. Several models are integrated in a GIS environment to develop an index of potential energy intake (IPI), aimed at reflecting the long term seasonal availability of invertebrate prey (mainly earthworms) on grasslands. The results are scale dependent. At the regional scale, they indicate that the most important variables influencing the demographic fragmentation are the availability of grasslands and soil moisture. It is shown that this translates into potential availability of spring and summer food resources, in the form of soil invertebrates. The results indicates that, at least in Scotland, the decline in quality of grasslands as a habitat for soil invertebrates, rather than that in winter cereal stubble, might have been associated with the past Rook population decline. At the landscape scale, no difference was found between IPI values around colonies, versus IPI values around wooded areas devoid of colonies, or between IPI and number of nests. It is hypothesised that conspecific attraction contributes to decoupling between resources and breeding density at the landscape scale. The results of this study support the hypothesis of Brown et al. (1995) that the distribution of a species might be understood in terms of the extent to which local environmental conditions meet the niche requirements, but highlight the importance to account for the scale at which such requirements are assessed.

Within the steppe-like western slope of the Peruvian Andes forest patches (dry cloud forests) occur from Ecuador to 13°S. Eight localities were studied between Huamba (4°41'S) and Zárate (11°55'S). A total of 145 bird species or 152 taxa (species and well marked subspecies) were recorded. The general distribution of the taxa supports the formerly discussed hypothesis that the majority of species arrived and colonised the western slopes from the north, but also suggests that eastern elements arrived to the western slopes south of the Porculla Pass (5°51'S), that some taxa evolved on the western slopes, and that southern elements complete the avifauna of the dry cloud forests. Six zones were identified as east-west exchange routes for birds. The northern origin of the majority of taxa is supported by three aspects, the marked diminution in species numbers from north to south; the pattern shown by 79% of the taxa suggesting a north to south dispersal of species along the slopes down to a limit determined by the humidity gradient and habitat conditions; and, the complex distribution patterns found in the Department of Ancash. Six main areas of taxa limits or replacement were identified that indicate that speciation processes on the western slopes have taken place mainly from <I>ca</I>. 7°30'S southward. The birds of the forests of central Peru consist of a mixture of permanent, seasonal, occasional and contaminant species. The avifauna is seasonal both in composition and abundance. Both are greatest from November to May and decrease to their lowest point in October. Insectivores and granivores are most abundant in May, frugivores in October and nectarivores show little annual variation. The main reproductive season in central Peru occurs in April and May.

The trends in the numbers of British breeding woodcock Scolopax rusticola and the Continental woodcock that visit Britain in winter were examined using ringing recoveries and bag records. The proportion of foreign: British woodcock present in S England and Wales is appreciably higher than in N England and Scotland. Average annual survival rates for adult British and foreign- ringed woodcock were estimated as 58% and 54% respectively. Calculations of the annual production of young woodcock, based on British Trust for Ornithology nest record cards from Britain and on data collected in NE Derbyshire, suggested that too few young woodcock are produced to compensate for the current rate of adult mortality among British woodcock. Woodcock chick mortality was the key factor in an analysis of 15 years of data from Derbyshire. Overwinter loss was density-dependent and the main regulatory, or k, factor. This is important because it means that the arrival of Continental woodcock in Britain in winter probably increases mortality among the resident British birds. A simulation model based on the Derbyshire data was used to estimate the maximum sustainable shooting yield and the effectiveness of shooting bans in cold weather. When feeding at night in winter, woodcock select grass fields in preference to arable fields and use areas dominated by grass. They probably select between the older fields on the basis of the relative availability of earthworms and other soil invertebrates, particularly leather]ackets, Tipulidae larvae. British woodcock are faithful to the natal or breeding site in winter and Continental woodcock exhibit lower wintering site fidelity. Woodcock experience higher mortality in cold winters, when freezing conditions prevent the birds feeding, and the recovery of the population following severe winters took three-year. Most cold weather movements within Britain are probably only made by Continental migrants. In the breeding season, woodcock selected areas of shrubby cover, typical of the edges of stands, within lowland mixed deciduous woodland. In an upland area of birchwood and heather moorland, feeding woodcock preferred dense young birch thickets although the birds nested in more open areas typically dominated by bracken Pteridium aguilinum and heather Calluna vulgaris. In both situations, the habitats used most intensively supported higher available densities of earthworms than habitats that were avoided. Clearly, conversion of grassland to arable fields will reduce the area of suitable habitat for woodcock in winter. The loss of managed coppice in Britain in the last 50 years has probably contributed to the decline in the British breeding population, because coppice provides ideal habitat for breeding woodcock. The fact that woodcock do not breed in SW Britain maybe due to increased overwinter mortality, because a high density of Continental woodcock occur there in winter.

Semi-natural wet grassland communities are rapidly disappearing from the farmed landscape. Protection of remaining areas and restoration of degraded areas has become a priority with organisations concerned with the conservation of biodiversity in the U.K. The research described in this thesis provides an insight into the community dynamics of one particularly rare plant community, the Cirsio-Molinietum fen meadow (NVC M24). This was achieved by examining the autecology of Cirsium dissectum, one of the key indicator species of this community. The habitat environment where C. dissectum is present was characterised at eight Devon M24 locations and ten non-M24 locations. This revealed a particularly unique suite of environmental conditions. Soil water content was found to be relatively high with little seasonal fluctuation. Mineral nutrient status was characterised by particularly low phosphorus, below optimal nitrogen, ample calcium and potassium and a soil pH which was only mildly acid. The physiological characteristics of C. dissectum were determined by a series of controlled experiments. The species exhibited a high water requirement but was relatively tolerant of drought stress and prolonged dehydration. It was demonstrated that C. dissectum is well adapted to a low phosphorus environment, is tolerant of nitrogen levels considered below optimum for many plants and is relatively tolerant of shade. It can also recover from partial or total defoliation in a relatively short period of time without any loss in plant mass or carbohydrate reserves. From the physiological characteristics, it was concluded that C. dissectum conforms to the &quot;stress-tolerant competitor&quot; functional type. It was also concluded that the decline of the species is directly related to loss of habitat as a result of its degree of specialism and specific niche requirement. The implications for management of existing sites and restoration of degraded sites is discussed and an outline model of appropriate management actions is presented.

No description available.

The red bishop bird, Euplectes orix, is a widespread and locally abundant member of the weaver family, the Ploceidae. It is found over most of Southern Africa, and as, far north as Uganda in the Eastern savannah belt. Large flocks may be found in association with other seedeaters, and the breeding colonies in reeds or tall grass in marshy areas may contain from five to several thousand birds. Recently it has also been recorded as nesting in standing crops in some areas. The adult birds are sparrow-sized, 12-15 cm in length and weighing 20-30 gm. The wing-length in the males ranges from 70-83 mm, and in females from 64-72 mm. Mackworth- Praed and Grant (1962) mention that birds from the Cape are larger, and that there appears to be a decrease in size of birds further north; measurements taken in this study seem to confirm this. During most of the year, both sexes are a mottled light brown colour, with a pale streak above the eye, and the underside pale to almost white, with darker streaks. However, at the beginning of the breeding season the adult males moult into their striking nuptial plumage: the abdomen and face mask are black, while the crown, throat, breast, rump, upper and under tail coverts are scarlet. The mantle feathers are tawny, but the wings and tail remain brown. The bill colour also changes from flesh-coloured to black. Hall and Moreau (1970), whose nomenclature is used for all the passerine species mentioned, regard three species Euplectes orix, franciscus and nigroventris as comprising the "orix superspecies". All three retain the brown wings and tail in the male breeding dress, but show variations in the extent of the red and black plumage. There is no apparent overlap in their ranges, or any evidence of inter-breeding. Two further species, E. hordeceu and E. gierowii, differ in that the wings and tail of the male are also black during the breeding season. Although slightly larger, their plumage is in other respects very similar, and these five species are termed a "species group". There is surprisingly little published information on any of these species. Lack (1935) first described territorial behaviour and polygyny in Euplectes hordeaceus, and later Moreau and Moreau (1938) and Fuggles-Couchman (1942) compared the ecology of E. hordeaceus and E. nigroventris. Skead (1956) produced a valuable basic study of E. orix, and showed it to be polygynous. Emlen (1957) made observations on several Euplectes species in Rhodesia, but the species orix and hordeaceus are confused in his paper, and it is not always clear which he is referring to. Later studies dealing with E. orix by Brooke (1964), Schmidt (1968) and Woodall (1971) are primarily concerned with clutch size, breeding seasons and nesting success, rather than behaviour. However, Crook (1962, 1963, 1964) has produced an important series of papers comprising a comparative study of behaviour in the entire weaver family. He refers mostly to the genus Euplectes, but also quotes observations on individual species, including E. orix. Collias and Collias (1964) have described nest-building behaviour in the weavers, but also mainly at the generic level.

The special ornithological advantage of KwaZulu-Natal is the massive altitudinal gradient between the coastline and the Drakensberg Mountains, an altitudinal range in excess of 3000 m. It is one of the best places in the world to study altitudinal bird migration. This dissertation uses the bird data from the Second Southern African Bird Atlas Project (SABAP2), and altitudinal data from a Digital Elevation Model to try to understand altitudinal migration in a band of KwaZulu-Natal between 29°S and 30°S. The bird atlas provides data on a five minute grid, grid cells with sides of c. 9km, known as pentads. The Digital Elevation Model gives spot heights at 0.5 minute intervals. It therefore provides 100 altitudes in each pentad. There is a description of the data analysis approach used to relate bird species abundance to altitude and selected examples to show how the method works, illustrating the strengths and weakness of the approach. The developed method is then applied to the study area to investigate altitudinal migration. For each of the 304 species which occur with some regularity in the study area, the altitudinal height preferences in summer and winter are plotted and compared. Some species, such as African Dusky Flycatcher, are definite altitudinal migrants, and some species are definite residents having essentially identical altitudinal distributions in summer and winter, such as Black-bellied Starling. There are also many intermediate strategies. Numerous species have been proposed as altitudinal migrants in KwaZulu-Natal. These claims are evaluated against the results obtains in this dissertation. For some species, the suggestion that they are altitudinal migrants is clearly incorrect, and for other species the hypotheses are confirmed by the bird atlas data. The project attempted to determine if there were common factors that helped explain which species engaged in altitudinal migration. A set of life history characteristics for each species, including aspects such as diet, mass, habitat, etc, was used to evaluate if there was a relationship between the extent of altitudinal migration and these explanatory variables. No meaningful relationships were found. Explanations of altitudinal migrations therefore remain an enigma.