Lead exposure is correlated with reduced nesting success of an urban songbird

Lead exposure is a concern in urban ecosystems, with physiological and
behavioral effects well documented in humans. Wildlife inhabiting urban
ecosystems are also exposed to lead, yet little work has documented the
sublethal effects of lead exposure in urban wildlife. We studied northern
mockingbirds (Mimus polyglottos) in three neighborhoods of New Orleans,
Louisiana, two with high soil lead and one with low soil lead, to better
understand how lead exposure may influence mockingbirds' reproductive
biology. We monitored nesting attempts, measured lead concentrations in
the blood and feathers of nestling mockingbirds, documented egg hatching
and nesting success, and assessed rates of sexual promiscuity in relation
to neighborhood soil lead levels. We found that nestling mockingbirds’
blood and feather lead levels reflected the lead levels of their
neighborhood soil lead level and nestling blood lead levels were similar
to adult mockingbirds in the same neighborhoods. Nest success, as
evaluated by daily survival rates, was higher in the lower lead
neighborhood. Clutch sizes varied substantially across neighborhoods, but
rates of unhatched eggs did not covary with neighborhood lead levels,
suggesting that other drivers are influencing variation in clutch sizes
and hatching success in urban habitats. At least one-third of nestling
mockingbirds were sired by an extra-pair male, and there was no
relationship between extra-pair paternity rates and neighborhood lead
levels. This study provides insight into how lead contamination may
influence reproduction in urban-dwelling wildlife and suggests that
nestling birds could serve as useful bioindicators of lead levels in urban
neighborhoods.