Abstract
Although several factors have been highlighted to explain the influence of urbanization on bird fitness and survival, the role of persistent toxicants such as lead (Pb), which is typically present in urban areas worldwide, has seldom been studied despite the ecological importance of such a widespread stressor. Studying free-living European blackbirds (Turdus merula) in city parks, we tested the hypothesis that low-dose chronic exposure to Pb could shape the life-history traits of urban birds. The feather concentrations of Pb and cadmium were typical of urban areas and low-to-moderate contamination of sites. Although the lifetime breeding success of females decreased with increasing exposure to Pb, the lifespan and survival probabilities of blackbirds increased with Pb contamination regardless of gender. Breeding effort-dependent patterns in the relationship between lifespan and Pb levels were highlighted. No significant relationships were detected between cadmium and life-history traits. The results suggest a possible trade-off between self-maintenance and reproduction, with the most affected birds redirecting allocations towards their own survival, which is consistent with the “stress hormone hypothesis”. These findings suggest that Pb pollution in urban environments may shape avian ecological features and be one of the drivers of wildlife responses to urbanization and that some urban areas may function as ecological traps driven by pollutants.
Highlights
Urbanization represents a major concern related to global change given the current trends in urban population growth and urban land cover expansion and is one of the most irreversible anthropogenic impacts on the global biosphere[1,2,3]
Could exposure to Pb be involved in shaping the ecology of urban birds? Our purpose was to investigate whether chronic low-dose exposure to Pb in urban environments could be a driver of life-history traits in the European blackbird, Turdus merula
If Pb-induced stress triggers a trade-off between self-maintenance versus reproduction, we predict that reproductive success and parental investment will decrease with exposure to Pb, whereas survival will increase and the relationship between productivity and lifespan will be shaped according to Pb exposure levels
Summary
Urbanization represents a major concern related to global change given the current trends in urban population growth and urban land cover expansion and is one of the most irreversible anthropogenic impacts on the global biosphere[1,2,3]. Most of the studies on Pb in terrestrial avian wildlife have been conducted in severely polluted areas, whereas the current level of pollution in cities has seldom been considered, and little is known about the effects of chronic low-dose Pb exposure despite the potential ecological importance of such a widespread stressor[23,31]. Our purpose was to investigate whether chronic low-dose exposure to Pb in urban environments could be a driver of life-history traits in the European blackbird, Turdus merula This omnivorous passerine bird is considered an urban adapter[33], it has been reported to exhibit differences in productivity and survival between urban and non-urban areas[8,9], and can be exposed to Pb through trophic transfer within food webs[34]. Gender-related differences in responses are expected, but their direction is unpredictable
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