Experimental manipulation of dietary lead levels in great tit nestlings: limited effects on growth, physiology and survival

Abstract

We manipulated dietary lead (Pb) levels of nestlings in wild populations of the great tit (Parus major L) to find out if environmentally relevant Pb levels would affect some physiological biomarkers (haematocrit [HT], fecal corticosterone metabolites [CORT], heat shock proteins [HSPs], erythrocyte delta-aminolevulinic acid dehydratase activity [ALAd]), growth (body mass, wing length), phenotype (plumage coloration) or survival of nestlings. The responses to three experimental manipulation (control, low and high: 0, 1 and 4 μg/g body mass/day) are compared with those in a P. major population breeding in the vicinity of a heavy metal source, a copper smelter. Our Pb supplementation was successful in raising the fecal concentrations to the levels found in polluted environments (high: 8.0 μg/g d.w.). Despite relatively high range of exposure levels we found only few effects on growth rates or physiology. The lack of blood ALAd inhibition suggests that the circulating Pb levels were generally below the toxic level despite that marked accumulation of Pb in femur (high: 27.8 μg/g d.w.) was observed. Instead, birds in the metal polluted environment around the smelter showed decreased growth rates, lower HT, higher CORT, less colorful plumage and lower survival probabilities than any of the Pb treated groups. These effects are likely related to decreased food quality/quantity for these insectivorous birds at the smelter site. In general, the responses of nestlings to metal exposure and/or associated resource limitation were not gender specific. One of the stress proteins (HSP60), however, was more strongly induced in Pb exposed males and further studies are needed to explore if this was due to higher accumulation of Pb or higher sensitivity of males. In all, our results emphasize the importance of secondary pollution effects (e.g. via food chain disruption) on reproductive output of birds.

No delayed behavioral and phenotypic responses to experimental early-life lead exposure in great tits (Parus major)

“…However, to cause severe long-lasting effects on cognition, developmental levels of Pb may have to be relatively high and acutely toxic. In our case, the nestlings in the Pb treatment did not show symptoms of acute toxicity: in a companion paper from the same study setup (Eeva et al 2014), we report that growth (body mass) was not impaired compared with the controls in our study (wing growth tended to even increase with low Pb exposure). Also, physiological biomarkers (hematocrite, fecal corticosterone, with the exception of HSP60) and especially a Pb-specific marker, Ala-D enzyme activity were not affected by Pb treatment in our study (results reported in Eeva et al 2014), suggesting that exposure levels were too low to cause acute toxicity.…”

“…On d7 and 14, chicks were measured (wing length and body mass). We ringed and collected a blood sample for molecular sexing (see details in Eeva et al 2014) and a fecal sample for noninvasive analyses of Pb levels on d7.…”

“…Birds in good condition were released to the wild in September. Eeva et al (2014). Briefly, we estimated the levels of Pb exposure in our experiment by concentrations in nestling feces and food items in passerine populations (for P. major and Ficedula hypoleuca) near pollution sources and at control areas, including Harjavalta, Finland (Eeva and Lehikoinen 1996;Eeva et al 2005Eeva et al , 2009), Antwerp, Belgium (Dauwe et al 2000(Dauwe et al , 2004, Rönnskär, Sweden (Berglund et al 2010;Nyholm 1994), and Revda, Russia (Belskii et al 1995).…”

“…The analysis is detailed in Eeva et al (2014). Briefly, blood was diluted in 0.9 % NaCl and six times SDS sample buffer and heated at 95°C.…”

Habitat urbanization and its effects on birds

“…Heavy metal pollution may pose both direct and indirect detrimental effects on birds' reproductive success. To assess their relative importance, a recent study (Eeva et al 2014) manipulated the dietary lead (Pb) levels at Great Tit Parus major nests, and compared these nestlings' physiological, biometrical and plumage traits to those of the nestlings living in a heavily polluted area (near a copper smelter). Despite of the similar exposure of lead in the treatment group and in the birds of the highly polluted area, chicks of the latter exhibited lower survival, decreased size and also the signs of inferior health state, compared to the treatment groups.…”