Marsh management, reserve creation, hunting periods and carrying capacity for wintering ducks and coots

Many wild species, like waterbirds, are exploited for their economic interests. At present, the annual western Palearctic duck bag is at least 17 million birds. From a sustainable management perspective, wetland users and managers request predictions of spatial distribution and abundance variations of these bird populations. The objective of this study was to analyze local factors potentially influencing the diurnal distribution and population size of wintering ducks and coots, the main game species, in Camargue (southern France). First, we showed that marshland surface area, salinity and hunting disturbance were the principal variables explaining the duck and coot distribution. Secondly, we tested the hypothesis that hunting disturbance would reduce the carrying capacity of the Camargue with two analyses: the effect of creating a protected area and the change of the hunting closing date. This hypothesis was not validated. Our study therefore led us to reconsider the research orientations on the carrying capacity in this wetland. The surface of protected day roosts seems presently sufficient in the Rhone delta. Consequently, to increase the population size with the same level of hunting disturbance at the scale of the Camargue, alternative strategies should be envisaged, such as the creation of nature reserves on nocturnal feeding ground or the creation of large management units with limited disturbance.