As a result of large industrial lead use in the past, many urban areas have elevated soil lead concentrations. Chronic, sub-lethal lead exposure is known to affect organ and neurological function in humans and captive animals, but the impacts on free-living urban wildlife remain poorly understood, especially in relation to potential impacts on behavior. We focused on the Northern Mockingbird Mimus polyglottos, a common, omnivorous North American songbird, to gain insights into how soil lead may affect the physiology and behavior of urban wildlife. We predicted that birds living in areas with high soil lead concentrations would exhibit (a) elevated lead concentrations in their blood, feathers, and eggs, (b) lower body condition, (c) less diverse and consistent vocal repertoires, and also that they would (d) behave more aggressively during simulated conspecific territorial intrusions. We studied mockingbirds in three neighborhoods in New Orleans, LA from 2014-2017 to address these questions.
Results/Conclusions
Consistent with our predictions, we found that birds from areas of high soil lead had concentrations in blood and feathers several times higher than those of birds from low soil lead areas. Also, birds from the high lead areas responded more aggressively during simulated intrusions than did birds from low lead areas. There was a non-significant tendency for birds in high lead areas to have reduced physiological condition, but no difference was found in the diversity or consistency of territorial song between neighborhoods. These findings corroborate the idea that chronic, sub-lethal exposure to lead may be common among wildlife living in contaminated areas, and are also consistent with the idea that this exposure may result in increased aggression. Better understanding the extent and consequences of lead exposure and associated increases in aggression for survival and reproduction are clear priorities for future work in this and other urban wildlife systems.