Les associations « gestionnaires » de l'espace : l'exemple du C.E.E.P.

International audienc

How slow breeding can be selected in seabirds: testing Lack's hypothesis

The historical debate of the 1960s between group and individual selection hinged on how the slow breeding of seabirds could be explained. While this debate was settled by the ascendance of individual selection, championed by David Lack, explanations for slow breeding in seabirds remain to be tested. We examined the slowest breeding of these birds, the albatrosses and petrels (order Procellariiformes), using analyses that statistically controlled for variations in body size and phylogeny. Incubation and fledging periods appeared strongly correlated, but this turned out to be largely explained by phylogeny. Nonetheless, developmental and reproductive rates were associated with the distance to the foraging range, as predicted under the hypothesis of ecological constraints on breeding pairs, and these results were independent of body size and phylogeny. Slower breeding in these seabirds appeared associated with the rigors of farther pelagic feeding, as Lack originally hypothesized

Foraging white-chinned petrels Procellaria aequinoctialis at risk: from the tropics to Antarctica

In the Southern Ocean white-chinned petrels Procellaria aequinoctialis form the majority of the bird bycatch in longline fisheries. Satellite tracking of breeding birds from the Crozet islands and from South Georgia indicates that during incubation they have the longest mean foraging ranges ever recorded for a seabird, 2390 and 2190 km. Crozet birds travel to the coast of South Africa at 3495 km, into subtropical waters as well as to Antarctic waters. South Georgia birds reach the northern Patagonian shelf. In all these areas birds are potentially in contact with fisheries. These results indicate that conservation measures limited to Antarctic waters are insufficient to protect seabirds with such extensive foraging ranges

Distribution and diet of juvenile Patagonian toothfish on the South Georgia and Shag Rocks shelves (Southern Ocean)

The distribution and diet of juvenile (<750 mm) Patagonian toothfish are described from 4 annual trawl surveys (2003-06) around the island of South Georgia in the Atlantic sector of the Southern Ocean. Recruitment of toothfish varies inter-annually, and a single large cohort dominated during the four years surveyed. Most juveniles were caught on the Shag Rocks shelf to the NW of South Georgia, with fish subsequently dispersing to deeper water around both the South Georgia and Shag Rocks shelves. Mean size of juvenile toothfish increased with depth of capture. Stomach contents analysis was conducted on 795 fish that contained food remains and revealed that juvenile toothfish are essentially piscivorous, with the diet dominated by notothenid fish. The yellow-finned notothen, Patagonotothen guntheri, was the dominant prey at Shag Rocks whilst at South Georgia, where P. guntheri is absent, the dominant prey were Antarctic krill and notothenid fish. The diet changed with size, with an increase in myctophid fish and krill as toothfish grow and disperse. The size of prey also increased with fish size, with a greater range of prey sizes consumed by larger fish

Efficacy and effects of diet sampling of albatross chicks

Although a variety of techniques (including water-offloading, and spontaneous and induced regurgitation) are used routinely to obtain fresh stomach samples from seabirds, there have been few studies of their efficacy or potential deleterious effects. In this study, sampling of Black-browed (Thalassarche melanophrys) and Grey-headed (T. chrysostoma) Albatross chicks by induced regurgitation had no effect on subsequent survival or fledging mass. In addition, the samples obtained were large (on average, 676 g and 756 g, respectively, which was 19% and 23% heavier than the average meal mass in a previous study). Notwithstanding the analytical biases associated with differential prey-digestion rates (which also apply to samples from adults), the advantages of this technique are that it is non-invasive, rapid (<1 min), requires minimal training and, compared with handling of adults, does not entail a desertion risk. Induced regurgitation of chicks is therefore highly recommended for routine monitoring of diet in Procellariiformes