Le Havre, France
Le Havre, France

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Jiguet F.,CNRS Science Conservation Center | Chiron F.,CNRS Science Conservation Center | Dehorter O.,CNRS Science Conservation Center | Dugue H.,Association ACROLA | And 9 more authors.
Acta Ornithologica | Year: 2011

The autumn world population of the endangered Aquatic Warbler Acrocephalus paludicola probably numbers between 23 000 and 69 000 individuals, including 5 000 to 44 000 first-year individuals, depending on variation in breeding success and post-fledging survival. After breeding, the species migrates as early as August along a westerly route along French coast to reach its African wintering grounds. In 2009, French ringers have carried out targeted mist-netting to enhance the capture of the species, using tape luring in suitable habitats. Overall, 874 different individuals were captured in France in that year. In 2010 similar ringing effort allowed the capture of 646 different individuals. From this ringing information, we propose a simple method to estimate the number of individuals which stopped in the country during the autumn migration, considering all birds or first-years only. Splitting the country in two parts (northern and southern), the method uses the total number of captures and the number of southern recaptures of birds first ringed in the north. Overall, we estimated that between 24 000 and 30 000 individuals most of them in their first calendar year stop in France each year during the fall migration. These estimates suggest that probably all first-year Aquatic Warblers migrate by this western flyway and stop in France to refuel, while adults may partly use a different flyway or may stop in France, but for shorter times or at fewer sites. The proposed figures highlight the importance of maintaining suitable refuelling habitats for the species all along coastal France.

Provost P.,Maison de lEstuaire | Klein A.-C.,Maison de lEstuaire | Prodon R.,E.P.H.E. Ecole de Biogeographie et Ecologie des Vertebres | Julliard R.,French Natural History Museum
Alauda | Year: 2013

Many bird species use reedbeds along the year in a Natural reserve of the Seine estuary. A large part (1,000 ha) of this reserve remains unmanaged and a small part is managed by horse grazing and reed cutting. The aim of this study is to quantify the impact of reed cutting and grazing on breeding passerines. The data used are those from the STOC ROZO national ringing scheme (collected from 2000 to 2009) and those based on songs in spring 2010. Areas under cutting showed a decrease of all reed-nesting species (winter cutting weakens the reeds). Grazing decreases the numbers of Eurasian Reed Warbler, Sedge Warbler, Cetti's Warbler and Grasshopper Warbler but increases those of Common Reed Bunting and Bluethroat. Small cutted areas mixed with patches of uncut reeds are optimal for breeding birds in reedbeds. A year with cutting followed by another of non-cutting will also improve reed quality and enhance biodiversity.

Provost P.,Maison de lEstuaire | Kerbiriou C.,CNRS Science Conservation Center | Jiguet F.,CNRS Science Conservation Center
Acta Ornithologica | Year: 2010

Stopover sites of migratory songbirds are of great importance in the context of the maintenance of a species migration strategy. Here we studied the spatial needs and habitat selection of the endangered Aquatic Warbler at a major migration stopover site in France, the nature reserve of the Seine estuary. We radio-tracked 15 migrant birds in August 2008 to study habitat use and selection at that stopover site, and analysed faeces and blow trap samples to determine the local diet of the species and to compare food availability among the different available habitats in the reserve. Range size was estimated with fixed kernels and was on average 9 ha (90% isopleths), with daily core ranges (50% isopleths) of just over 1 ha. There was no variation in range size or habitat use during the survey period (August) or during an individual stopover stay. Studying habitat selection within the modelled ranges, we found that the species displayed a preference for wet grassland habitats. Larger daily ranges included more reedbed and fewer grassland areas. This matches the habitat preferences known from breeding and wintering grounds. The main identified prey belonged to a few invertebrate orders, with Odonata, Lepidoptera, Coleoptera and Araneida making the largest contributions to the biomass consumed. There was no significant difference in invertebrate availability between grassland and reedbed habitats in the study area. The availability of grassland habitats close to the reedbeds appears to be a key parameter to ensure the rapid and efficient refuelling of migrant Aquatic Warblers during their autumn migration.

The Aquatic warbler breeds in fen mires and similarly structured habitats. It was formerly an abundant breeding bird throughout Central and Eastern Europe. Since 1990 the species lost most of its breeding range west of the Polish-German border due to large-scale habitat destruction and became the only globally threatened songbird of the European mainland with a world population of only 10,20014,200 singing males. On postnuptial migration the northern and Atlantic coasts of France host the largest numbers of Aquatic Warblers in West Europe. In several years many birds have been mist-netted, mainly in August. A few radio-tracked birds at two sites Seine Estuary and Baie d'Audierne in Brittany provided data on home range and habitats. The availability of wet grassland habitats less than 1 m high close to reedbeds near open waters appears to be a key habitat to ensure the rapid and efficient refuelling of Aquatic Warblers during their postnuptial migration on the western coast of France. This study allowed to define some recommendations to maintain or restore suitable habitats for the species during its postnuptial stopovers.

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