City noise as a potential stressor on the urban bird : an analysis of heterophil/lymphocyte ratios in European Starling nestlings

Abstract

Anthropogenic disturbances are known to induce stress in a variety of rban species. This study aims to determine if one particular disturbance, ambient urban noise, influences the stress levels of nestling European Starlings (Sturnus vulgaris). Nest boxes were randomly assigned to either an experimental (increased urban noise level) or a control treatment (normal ambient noise). Heterophil/lymphocyte (H/L) ratios were determine and used to estimate stress levels of nestlings at 11 and 15 days of age (day 0 being day of hatch). Higher H/L ratios are associated with increased stress levels. I predicted that nestlings in the experimental treatment would have higher H/L ratios than those in the control group. I also predicted that habituation or sensitization to the noise would occur; therefore nestlings would have either lower or higher H/L ratios on day 15 than on day 11. No significant difference in H/L ratios was detected between the two treatments at day 11. However, at day 15, control nestlings had significantly higher H/L ratios than did experimental nestlings. Experimental nestlings tended to have a lower H/L ratio at day 15 than at day 11, but no such pattern was detected in control nestlings. These findings suggest that, contrary to my prediction, constant loud noise may not be as important to inducing stress in urban-­‐thriving European starling nestlings as was previously thought. A future avenue of research would be to examine how the unpredictability of noise affects H/L ratios in this species.