Reproductive effects of heavy metal accumulation on breeding feral pigeons (Columba livia)

To investigate the effects of heavy metal accumulations on breeding birds, we compared the egg size, eggshell thickness and some reproductive parameters in feral pigeon populations collected from Seoul and Ansan colonies. The results showed that concentrations of Pb in bone and Cd in kidney of adult pigeons in Seoul were three times higher than in Ansan colony. Significant positive correlation was also observed between Pb and Zn in bone and Cd and Zn in kidney of adult pigeons from Seoul, but not Ansan. This indicates that pigeons at Seoul may be affected more by the toxic Pb and Cd exposure in the environment rather than those at Ansan because of the antagonistic action of Zn against Pb and Cd toxicity. No significant difference was observed in egg characteristics (egg length, width and shell thickness), clutch size (number of eggs per clutch), incubation periods and hatchability of squabs between the two study sites. Although no significant difference was observed, body weight, and primary wing, bill and tarsus lengths of nestlings from Seoul which is more polluted were rather smaller than those from Ansan. Nestlings at Seoul fledged significantly later than at the less polluted site (Ansan). We also observed significantly lower fledging success at Seoul than Ansan colony. Elevated metal exposure may thus result in decreasing growth rate in pigeon nestlings resulting in fledging length and fledging success. Our results suggest a possible effect of heavy metal bioaccumulation on breeding of feral pigeons.