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International audience; Ungulate populations exhibiting partial migration present a unique opportunity to explore the causes of the general phenomenon of migration. The European roe deer Capreolus capreolus is particularly suited for such studies due to a wide distribution range and a high level of ecological plasticity. In this study we undertook a comparative analysis of roe deer GPS location data from a representative set of European ecosystems available within the EURODEER collaborative project. We aimed at evaluating the ecological factors affecting migration tactic (i.e. occurrence) and pattern (i.e. timing, residence time, number of migratory trips). Migration occurrence varied between and within populations and depended on winter severity and topographic variability. Spring migrations were highly synchronous, while the timing of autumn migrations varied widely between regions, individuals and sexes. Overall, roe deer were faithful to their summer ranges, especially males. In the absence of extreme and predictable winter conditions, roe deer seemed to migrate opportunistically, in response to a tradeoff between the costs of residence in spatially separated ranges and the costs of migratory movements. Animals performed numerous trips between winter and summer ranges which depended on factors influencing the costs of movement such as between-range distance, slope and habitat openness. Our results support the idea that migration encompasses a behavioural continuum, with one-trip migration and residence as its end points, while commuting and multi-trip migration with short residence times in seasonal ranges are intermediate tactics. We believe that a full understanding of the variation in tactics of temporal separation in habitat use will provide important insights on migration and the factors that influence its prevalence.

A complèter : pagination et WOS; International audience; Large wood (LW, or pieces of dead wood longer than 1 m and thicker than 10 cm in diameter) is a key element in forested streams, but its abundance has decreased worldwide as a result of snagging and clearing of riparian forests. Therefore, many restoration projects introduce LW into stream channels to enhance geomorphology, biotic communities, and ecosystem functioning. Because LW enhances the retention of organic matter and sediments, its restoration can reduce siltation in receiving reservoirs, although so far little information on this subject is available. We studied the effects of restoring the natural loading of LW in four streams in the Aiako Harria Natural Park (the Basque Country, Spain) in pool abundance, channel form, and storage of organic matter and sediments. In all reaches log jams induced the formation of new geomorphic features and changes in physical habitat, especially an increase in the number and size of pools and in the formation of gravel bars and organic deposits. The storage of organic matter increased 5- to 88-fold and streambed level rose 7 ± 4 to 21 ± 4 cm on average, resulting in the storage of 35.2 ± 19.7 to 711 ± 375 m3 (733–1400 m3 ha− 1 y− 1) of sediment per reach. Extrapolation of these results to the entire drainage basin suggests that basinwide restoration of LW loading would enhance the retention potential of stream channels by 66,817 ± 27,804 m3 (1075 m3 ha− 1 y− 1) of sediment and by 361 t (5.32 T ha− 1 y− 1) of organic matter, which represents 60% of the estimated annual inputs of sediments to the downstream Añarbe Reservoir and almost twice as much as the annual input of organic matter to the entire river network. Therefore, basinwide restoration of LW loading is a potentially important tool to manage catchments that feed reservoirs, where retention of sediments and organic matter can be considered important ecosystem services as they reduce reservoir siltation.

International audience; We investigated space-use patterns of the West African savanna buffalo (Syncerus caffer brachyceros), a little-studied subspecies occurring at the northern limit of the African buffalo's geographical range. This buffalo generally ranges in small herds (about 45 individuals) and has a low body mass (approximately 400 kg) relative to the Cape buffalo (S. c. caffer). We monitored the movements of 7 breeding herds in W Regional Park (Burkina Faso, Benin, Niger) using global positioning system collars and activity data loggers. Habitat selection was analyzed at both large (interseasonal) and small (intraseasonal) scales in a context where resources are segregated spatially at some times of year. Both biotic (primary production and vegetation types) and abiotic (timing of rainfall and surface water) covariates, and the extent to which neighboring herds shared space, were considered. In the dry season buffalo herds ranged close (within 5.3 +/- 2.0 km, mean +/- SD) to segments of permanent rivers. At the onset of the monsoon all herds but 1 (which had year-round access to suitable resources) performed a large (35 +/- 10 km) directional movement in response to a large-scale gradient of primary production. Spatiotemporal dynamics of forage and water resources thus jointly stimulated interseasonal directional movements and shaped large (335 +/- 167 km(2)) annual home ranges. Furthermore, the establishment of home ranges in the wet season appears to be conditioned by a threshold (about 10%) in the availability of perennial grasses. Habitat-selection analysis at intraseasonal scale also underlines the key role played by perennial grasses for buffaloes. The spatial arrangements of home ranges of neighboring herds also suggest that interherd behavioral avoidance is a high-level constraint on foraging processes. The ability of the African buffalo to cope with contrasting environmental conditions throughout most sub-Saharan ecosystems highlights the high behavioral plasticity of this species.