High densities of the french coastal endemic bluethroat (Cyanecula svecica namnetum) revealed in intertidal reed beds and conservation perspectives towards sea level rise

Our study deals with density estimation in intertidal reed beds of the Gironde estuary (France) of the French endemic subspecies of Bluethroat breeding along the Atlantic coast (Cyanecula svecica namnetum). We analysed count point data collected during the beginning of the breeding period, with information gathered from 94 stations distributed over 100 hectares. Analysis of data integrating bird detection probability as a function of the detection distance (distance sampling) allowed us to estimate an average density of 20.5 ± 3.7 males for 10 hectares (14.4 – 29.5 within the 95 % CI). Up to now, no equivalent densities have been documented for this endemic taxa which is of conservation concern given its relatively high degree of specialization in terms of ecological resources exploited and its limited range and numbers. Despite their singularity given the limited size of the study area, our results confirm the particular importance of coastal marshes for C. s. namnetum. In view of strong alterations of coastal habitats due to the rise in sea level already observed in the breeding grounds of C. s. namnetum, our results highlight the interest in developing conservation strategies for habitats exploited by the taxa, integrating the potential key roles of back littoral areas in order to compensate losses of habitats due to the ongoing and forthcoming effects of global changes.