Exposure to lead (Pb) contamination paradoxically heightens predator avoidance behaviours in an urban bird

To survive, prey animals must correctly assess and respond to predation, by vigilantly scanning their environment for threats, assessing predation risk through gaze aversion (responding fearfully to predator gaze), and escaping efficiently. As these anti-predatory behaviours are integrated through the nervous and motor systems, they could be disrupted by neurotoxic contaminants, such as lead (Pb), which is ubiquitous in the Anthropocene. Here, we examined the effects of Pb on anti-predatory behaviours of free-living house sparrows (Passer domesticus), in the mining city of Broken Hill, Australia, where birds have been exposed to elevated Pb levels for many generations. We found that sparrows in higher-Pb contaminated areas spent more time scanning their surroundings and were more reluctant to approach a feeder under direct, experimentally introduced human gaze, than sparrows in lower-Pb contaminated areas. Higher-Pb birds had slightly worse (though not statistically different) escape flight performance than their lower-Pb counterparts. Our results suggest that greater exposure to Pb is associated with increased fear, which may or may not be linked to Pb-compromised escape performance. We highlight the importance of considering multi-faceted, integrated effects of environmental pollution on the behaviours of urban wildlife.