Concentration of Heavy Metals in Feathers of Little Egrets (Egretta garcetta) in Three Coastal Breeding Colonies in Spain

Supervisors: Maite Martínez, Pilar Rodriguez (UPV/EHU)
Heavy metal pollution in aquatic ecosystems is of great concern today due to its persistence in the environment and ultimate damaging effect on wildlife. The assessment of metal bioaccumulation in birds is a relevant tool to evaluate ecological risk due to metal pollution in aquatic ecosystems, as well as to ensure effective protection of catalogued species. Heavy metal bioaccumulation of Cd, Cr, Cu, Hg, Ni, Pb and Zn by Little Egret (Egretta garzetta), a common colonial waterbird was assessed by means of chick feathers, in three different locations on the Spanish coast: in the north, Izaro Island (Urdaibai Biosphere Reserve, Bizkaia) and San Pedro Island (Natural Park of the Marshes of Santoña, Victoria and Joyel, Cantabria); and in the south, Enmedio Island (Odiel Marshes Biosphere Reserve, Huelva). Although they are all found in protected areas, the Odiel Marshes present the additional factor of being surrounded by a historically polluted area. For this purpose, breast feathers of Little Egret chicks were collected during the 2013 breeding period. There were no significant differences for Cd, Ni, Pb and Zn found in the metal residue in feathers collected from the three study sites. However, Hg levels were approximately three times lower in Odiel than at the two other sites and Cr and Cu presented higher levels in Odiel. In general terms, the three study sites showed low bioaccumulation levels of heavy metals in the feathers of Little Egret chicks, although Hg levels showed moderate levels in Urdaibai due to local pollution, but were below the threshold values reported to cause adverse effects and alterations in bird reproduction. In contrast, with its low level of pollution, Odiel might be regarded as a reference site concerning Hg. Cu levels showed higher bioaccumulation in birds from Odiel comparing to what has been reported elsewhere, which is matter of concern and research. Bioaccumulation levels in feathers of the Little Egret colony in Urdaibai were compared with those measured in feathers of Yellow-Legged Gull (Larus michahellis) at the same location. Differences were found between the species: Cu was the metal with higher concentration in Little Egret, whereas Yellow-legged Gull accumulated mostly Zn, Ni, Cd and Pb, reflecting the different feeding regimes of these two species.