Lead shot ingestion by marsh harriers Circus aeruginosus from the Ebro delta, Spain

摘要

Breeding marsh harriers disappeared from the Ebro delta in the l980s. Although marsh harrier breeding populations have recently increased in other wetlands of NE Spain, recolonization by breeding birds has not been observed in the Ebro delta, despite the fact that it is an important wintering area for the species. Lead (Pb) poisoning in marsh harriers, a problem described in other European wetlands, has been studied as a possible cause of this breeding impairment. Around 11 of harrier pellets (mainly with duck remains) contained Pb shot, and 52.5 of marsh harriers had blood [Pb] higher than 200 ng ml~(-1). Maximum values for both parameters occurred in the middle of the hunting season. Blood [Pb] of wing-tagged marsh harriers classified as wintering birds was higher than those classified as migrant birds, and Pb levels decreased at the end of the hunting season. Body condition was not affected by blood [Pb], and none of the marsh harriers found dead had died of Pb poisoning. Birds with blood [Pb] higher than or equal to 601 ng ml~(-1) returned to the Ebro delta in the next winter in a lower proportion (1/3) than birds with blood [Pb] lesser than or equal to 200 ng ml~(-1) (6/6), although this difference was not statistically significant (P= 0.083). Pb poisoning may affect popu- lations of wintering marsh harriers, but other ecological and behavioural aspects have to be considered as well to explain the lack of breeding recolonization of the Ebro delta.