Growth and mortality of nestling great tits (Parus major) and pied flycatchers (Ficedula hypoleuca) in a heavy metal pollution gradient.

We studied nestling growth, growth abnormalities, mortality and breeding success of two hole-nesting passerines, the great tit (Parus major) and the pied fly-catcher (Ficedula hypoleuca), at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland in 1991-1993. The main pollutants in the area are heavy metals and sulphuric oxides. Exposure of birds to heavy metals was shown by measuring their faecal concentrations. Copper, nickel and lead contents of nestling faeces were high near the factory and decreased with distance away from the pollution source. F. hypoleuca nestlings suffered high mortality very close to the factory complex, but did relatively well at all other sites. Breeding success of P. major was below background levels up to 3-4 km from the pollution source and nestlings grew poorly close to the factory. Growth abnormalities of legs and wings in F. hypoleuca nestlings were significantly more common near the factory than farther away. In contrast, F. hypoleuca nestlings grew equally well at all distances. The poor breeding success of F. hypoleuca close to the factory complex is probably related to the high amount of heavy metals in its diet, and low availability of calcium-rich food items may enhance this effect. We suggest that the poor breeding success of P. major is related to habitat changes that have taken place around the factory. The different responses of these two bird species are probably due to their different diet. Our results show convincingly that species-specific differences in response should be carefully considered when planning schemes for air pollution monitoring.