Biomarkers and fluctuating asymmetry as indicators of pollution-induced stress in two hole-nesting passerines

1. The stress caused by air pollutants was studied at biochemical, morpholo gical and ecological levels in the Pied Flycatcher, Ficedula hypoleuca, and Great Tit, Parus major, nestlings in 10 study sites along the pollution gr adient of a copper smelter. 2. First, stress was measured using four biomarkers from blood and liver: e thoxyresorufin O-deethylase (EROD) enzyme, haemoglobin, stress protein Hsp7 0 and delta-aminolevulinic acid dehydratase (ALA-d) enzyme. Second, the amo unt of fluctuating asymmetry (FA) in the length of the 3rd primary and the outermost rectrix (in P. major) and the length and thickness of the tarsus were measured. These stress indicators were further examined in relation to the breeding performance of birds, i.e. the ecological response. 3. EROD activity was increased in F. hypoleuca nestlings near the pollution source. In P. major, it was not related to the pollution gradient but corr elated well with the proportion of starved nestlings, i.e. the nutritional stress during the nestling period. The variations in haemoglobin, Hsp70 and ALA-d enzyme activity were not significantly related to pollution gradient . 4. The tarsus length of F. hypoleuca nestlings and primary length of P. maj or nestlings showed increased asymmetry in the vicinity of the pollution so urce. Breeding success decreased towards the pollution source in both speci es. 5. In F. hypoleuca, the pollution-related stress was verified at all three target levels. In P. major, pollution-related effects were found at morphol ogical and ecological levels but not at the biochemical level, which sugges ts that direct toxic effect of heavy metals was not the main mechanism in t his species.