The feathers of greater flamingo (Phoenicopterus roseus) fledglings collected from six colonies (Odiel, Delta Ebre, Camargue, Cagliari, Comacchio and Venezia) of the western Mediterranean Sea were used as biomonitors of metal contamination of coastal wetlands, with a particular focus on mercury. We used single and pooled samples, attempting to minimise the critical factors typical of studies on metals in feathers by: sampling birds of the same age, during the same breeding season; sampling the same type of feather; treating the feathers in the same way and at the same time; and analysing the same digested solution as a single batch and in two different laboratories applying different techniques. Flamingos from Cagliari, a site known for its mercury contamination, had maxima and median values greater than any of those from the other sites in terms of both single and composite samples. There were also high concentrations at the other sites, which in the absence of literature evidence of Hg pollution, suggests either the existence of pollution or that adults are foraging in contaminated wetlands. The flamingo population of Odiel had the lowest median and dispersion of Hg, and is possibly a baseline for the western Mediterranean greater flamingo population.