Environmental impacts on wetland birds: long-term monitoring programmes in the Camargue, France.
Résumé
Wetlands in the Mediterranean area have become a rare habitat due to human impact. To model the ecology and breeding biology of birds depending on that habitat, we describe long-term studies on two wetland birds (Little Egret Egretta garzetta and Greater Flamingo Phoenicopterus (ruber) roseus) in the Camargue, France. The hydrological conditions in natural Mediterranean wetlands depend largely on the pattern of rainfall (winter) and evapotranspiration (summer), but have been substantially altered by human activities. In natural conditions, these wetlands are very diverse and therefore sustain a high diversity of breeding birds. At the same time their unpredictable nature favours opportunistic breeding and wintering strategies of their inhabitants. Colonial waterbirds depend on wetlands both for safe nesting sites and for foraging. Availability of suitable nesting sites may limit breeding numbers. Availability and diversity of wetland habitats as foraging sites affect the number and density of breeding species that an area can sustain. Unfavourable feeding conditions can reduce the number of birds that attempt to breed and the number and quality of offspring the birds produce. Apart from local environmental factors, dispersal between wetlands in the western Mediterranean and existence of a non-breeding pool also affect breeding numbers in the Camargue. Thus, the persistence of wetland birds in the Mediterranean depends both on a network of habitat types on a local scale and a network of wetlands on a regional scale.