Lead (Pb) is a common pollutant in urban soils known to cause significant health problems in humans, including mental retardation among children. Scavenging wildlife commonly also suffer acute lead poisoning due to ingestion of lead shot; however, little is known about the effects of chronic sublethal lead exposure on urban wildlife. In the City of New Orleans, Louisiana, where lead exposure is considered a key public health issue, we studied Northern mockingbirds (Mimus polyglottos) from neighborhoods with varying background lead levels. Previous work shows that mockingbirds from neighborhoods with high background lead levels also have higher concentrations of lead in their blood and feathers and behave more aggressively towards a simulated territorial intrusion. We investigated whether this increased aggressiveness is associated with increased reproductive success (e.g., via better mate guarding or access to superior resources) or reduced reproductive success (e.g., via inattentiveness to offspring, impaired sperm production and quality, and/or direct impacts on nestling health and survival). We predicted that lead exposure would be associated with increased nest infertility, decreased nestling body condition, and decreased nestling survival.
Results/Conclusions
Contrary to our predictions, we found no effect of neighborhood lead level on nesting success, as measured by clutch size, egg size, and nest failure rate. Interestingly, nestlings in the high-lead neighborhoods had slightly better body condition. Our results suggest that increased aggression due to environmental lead exposure is not associated with adverse effects on nestlings. Further research is needed to understand how behavioral and reproductive impacts of sublethal exposure to lead may impact urban and suburban wildlife.