Traffic noise as a potential stressor to offspring of an urban bird, the European Starling

Anthropogenic disturbances induce stress in a variety of urban species. We examined the effects of traffic noise on the physiological stress response of nestling European Starlings ( Sturnus vulgaris ). Nest boxes were randomly assigned to either an experimental (increased urban noise played in nest box) or a control (typical urban/ambient noise) group. Heterophil/lymphocyte ( H / L ) ratios were determined to estimate physiological stress of nestlings at 11 and 15 days of age. Higher H / L ratios are associated with increased stress responses in birds. We predicted that nestlings in the experimental treatment would have higher H / L ratios and lower condition and fledging success than those in the control group on both days 11 and 15, but we detected no such differences on either day. Day 15 experimental nestlings, however, showed a non-significant trend toward lower H / L ratios than did day 15 control nestlings. We also examined whether nestlings became habituated (lower H / L ratios on day 15 than day 11) or sensitized (higher H / L ratios on day 15) to urban noise over time. There was a non-significant trend for experimental nestlings to have lower H / L ratios on day 15 than day 11, but no such pattern was detected in control nestlings. Our findings suggest that constant traffic noise is not stressful to nestlings in this urban-thriving species.