Showing papers by "Royal Society for the Protection of Birds published in 1994"

Collisions against fences by woodland grouse in Scotland

Abstract: A study was carried out in native pinewoods at Abernethy and Glen Tanar to investigate the effect of forest fences on capercaillie and black grouse. Collisions occurred at a rate of 0.25 and 0.03 per km of fence per month for capercaillie and black grouse respectively. Male capercaillie had a higher proportion of severe and fatal collisions than females. Capercaillie tended to collide with those sections of fence where there were moderately sized pines (8.5 m) close (within 4.4 m) to the fence. Collision sites close to trees were most strongly associated with the height of exposed trunk, suggesting that capercaillie fly under the canopy and fail to see the fence. The annual mortality rate of radio-tagged capercaillie caused by collisions was 32 per cent indicating that this was a major mortality factor. Collisions were most frequent between September and November when capercaillie were dispersing. It is recommended that fences are removed where and when they are unnecessary, or are made more visible, or are set back from old woodland.

Use of preferred nesting habitat by stone curlews Burhinus oedicnemus in relation to vegetation structure

Abstract: The stone curlew is a nocturnal bird which nests and forages on sparsely vegetated ground. Its population and geographical range in Britain have declined throughout the 20th century. Estimates of the size of a sub-population in the Breckland region of eastern England show that a decline which began in the 1940s or earlier continued up to the mid-1980s, but that the population was stable from 1985 onwards. A survey in 1987 indicated that stone curlews nested at the highest densities on fragments of formerly much more extensive short semi-natural dry grasslands and heaths (referred to throughout as heathland). However, most pairs bred at much lower density on spring-sown tilled farmland. An important part of the decline in the Breckland stone curlew population between 1968 and 1991 is attributable to a decline in the number of pairs nesting on heathland. Observations of stone curlews marked individually with colour rings showed that individuals did not nest exclusively on heathland or arable farmland. Some birds nested in both habitats in the same year and there were frequent moves between habitats from one year to the next. Year-to-year changes in the number of pairs of stone curlews nesting on heathland during a period of population stability were associated with variation in both the rate of return to heathland of ringed birds which previously nested on heathland and the proportion of surviving young adults with no previous breeding experience which nested on heathland. Some of the birds which were displaced from, or failed to recruit to, heathland nesting sites nested on arable land, but there was also evidence that a proportion of them did not attempt to breed. Measurements of sward height at heathland sites with a recent history of occupation by nesting stone curlews show that those sites which had been abandoned had taller swards than those where the birds remained. An index of the biomass of green vegetation was derived from satellite imagery obtained before and after a sharp decline in the number of heathland nesting stone curlews. It was found that the index had increased significantly more at heathland sites which had ceased to be used by stone curlews than at sites which continued to be used for nesting. The long-term decline in the number of stone curlews nesting on heathland is believed to have begun with the conversion of large areas of heathland for arable agriculture and forestry. However, it has continued during a period when little heathland was lost. Changes in vegetation structure and species composition associated with a reduction in grazing by rabbits and livestock are the most likely cause. Since 1985 breeding success has been enhanced by protection of eggs and chicks in arable crops from destruction by farming operations. Beginning in 1989 efforts have also been made to change the management of Breckland heaths. These include shallow ploughing and increased grazing by livestock, supported by payments from government under the Environmentally Sensitive Areas scheme. The number and proportion of stone curlews nesting on heathland has increased and the decline in the total population size has ceased. The relative contribution of different management factors to this change is not yet clear.

The status and distribution of Nightjars Caprimulgus europaeus in Britain in 1992. A report to the British Trust for Ornithology

Abstract: In 1992 the British Trust for Ornithology and the Royal Society for the Protection of Birds organized a national survey of Nightjars. A total of 3093 churring males was located and the British population was estimated to be approximately 3400 males. This represents an increase in numbers of more than 50% since the last national survey in 1981. Possible reasons for this partial recovery after a long period of decline are discussed.

Inter- and intra-annual variation in the occurrence of organochlorine pesticides, polychlorinated biphenyl congeners, and mercury in the eggs of a river passerine

Abstract: Failed eggs were collected from the nests of a river passerine, the dipper Cinclus cinclus, in Wales and southwestern Ireland during 1988–1992 and analyzed for up to 24 pollutants including 15 individual PCB (polychlorinated biphenyl) congeners.

Vegetation of Pande and Kiono Coastal forests, Tanzania

Abstract: East African coastal forests possess considerable botanical importance as an area of high plant endemicity, but are little known ecologically. Quantitative botanical sampling techniques have been used to determine vegetation communities in Pande and Kiono coastal forests, Tanzania. Data from 76 quadrats established in six transects (three in each forest) and containing a total of 146 plant species have been classified using TWINSPAN. Seven species-associations and four sample-associations are recognised. Undisturbed forest supports six species-associations which are rich in plant species of restricted distribution, and these differ between the sites studied. Forest heavily disturbed by man supports one species-association composed of more generalist forest species and this association is similar between sites. Variation in vegetation types of undisturbed forests appears to be caused by edaphic conditions, rainfall and degree of exposure. Variation in the vegetation of disturbed forests appears to be controlled by the intensity of forest disturbance. Heavy human disturbance of coastal forests reduces their biodiversity values as plant-diversity and the habitats of rare plant species are lost.