Ecologie de migrateurs tropicaux dans une zone préforestière de Côte d’Ivoire

Rollers (Coraciadidae) and Ree eaters (Meropidae) have been studied during three years in a guinean savanna — with galleries and patches of dense forest — in the Ivory Coast. Annual censuses of the breeding populations of savanna Rollers have been made by dilferent methods. For the two species a mean density of 1 individual per 4 or 5 hectares has been recorded with a production of young of 22 to 26 %, mainly in May. Three pairs of related species ( Merops gularis and M. albi- collis ; Eurystomus gularis and E. glaucurus ; Coracias cyano- gaster and C. naevius) are compared from an ecological and phy siological stand-point. The first-mentioned species of each pair is sedentary, the second migratory. Two of the three sedentary species are forest birds, while all the migrants are savanna birds, with the exception of M. albicollis which also lives in cleared and cultivated forest. Competition is avoided between the two popu lations through the occupancy of separate ecological niches. Congeneric species live in dilferent biotopes (or at least vege tation layers). Sedentaries hunt more easily in and around dense vegetation (adaptation to the conditions prevailing during the wet season), while the migrants prefer the most open spaces. The diet of the resident birds is more varied, the migratory species being more specialised in their feeding on swarms of winged ants and termites. Migratory species are much better adapted to the exploi tation of this seasonal production or to the appearance of newly accessible prey (ground insects on recently burnt patches of savanna), being able to move rapidly from one place to another and to concentrate locally in large numbers. Dates of arrivals and departures are compared with the calendar of rains and it is suggested that the timing of the migra tory movements in the northern part of the breeding area of these birds is more under the dépendance of the seasons than influen ced by local conditions. But it is possible that the rainy season in the Ivory Coast would be too wet to allow a good survival for the populations of these species ; this could also explain the disappea rance of our breeding Eurystomus glaucurus from June to Sep tember. Merops albicollis, a typical intra-african migrant, shows a premigratory fattening of about 7 %. This occurs at the end of the prenuptial moult and coincides with the beginning of the increase in the size of the gonads

Population change of Common Buzzards Buteo buteo in central southern England between 2011 and 2016

Capsule: Distance sampling identified an increase in estimated population size of Common Buzzards Buteo buteo in central southern England between 2011 and 2016 of more than 50%. The rate of population growth slowed in later years. Aims: To assess the utility of a targeted distance sampling protocol to derive seasonal and annual population estimates for Common Buzzards across an area of southern England. Methods: We used a line transect survey methodology and multiple covariate distance sampling to assess population density and abundance of Common Buzzards in spring and autumn between 2011 and 2016 across a 2600 km2 area of central southern England. Results: Estimated population size increased by more than 50%, from approximately 2900 to 4500 individuals, across the period in a trend similar to that shown by Breeding Bird Survey data. Discussion: A slowing of the growth in population size of Common Buzzards in central southern England suggests that the species may be approaching carrying capacity in this area. These results also suggest that currently employed broad scale survey methodologies adequately reflect the general population trends for this species. Our data provide the first published estimates of the Common Buzzard population in central southern England derived from direct empirical assessment

La pression de prédation estivale du Busard cendré Circus pygargus L. sur les populations de Microtus arvalis en Vendée

Although the Montagu’s Harrier feeds almost exclusively upon the Common vole in the area studied, it appears unable to exert any significant influence on the vole’s population cycles

Projet du parc national dans le sud de la Guyane francaise: propositions preliminaires basees sur une etude de peuplement d'oiseaux

SIGLECNRS RP 185 (1500) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Improvement of 93mNb and 103mRh activity measurement methodology for reactor dosimetry

Reactor dosimetry is based on the analysis of the activity of irradiated dosimeters, such as 93mNb and 103mRh. The activity measurement of these dosimeters is conventionally performed by X-ray spectrometry, but the low-energy of emitted photons makes it difficult to derive reliable results with low uncertainties. Approaches to improve these characterisations are presented: they include high accuracy efficiency calibration of a HPGe detector using both experiments and Monte Carlo simulation, calculation of corrective factors for the geometry (selfabsorption) and self-fluorescence effects. Improvement of the knowledge of the 103mRh decay scheme is also required and a specific experiment is proposed, including activity measurement of a 103mRh solution by liquid scintillation, and measurement of the photon emission intensities by X-ray spectrometry. A method for calculating coefficients to take into account the self-fluorescence effects in dosimeters is also suggested to improve the uncertainties on activity measurements