Monitoring corticoid metabolites in urine of white-tailed sea eagles: Negative effects of road proximity on breeding pairs.

The white-tailed sea eagle (Haliaeetus albicilla) is known to be sensitive to disturbance. To better understand potential stressors, we measured corticosterone metabolite levels in H. albicilla excreta and recorded the nest success of breeding pairs. We tested the ability of four enzyme immunoassays (EIA) to measure urinary glucocorticoid metabolites (uGM) in the excreta of one adult female eagle subjected to a controlled physiological stress treatment. We identified corticosterone-21-HS to be the most sensitive EIA to changes in uGM concentration. To exclude a sex bias, we confirmed the assay's applicability with samples collected from similar stress treatments in two juvenile males. We used the identified EIA to measure uGM in wild breeding pairs and tested effects of disturbance. Breeding pairs nesting closer to roads and paths had higher uGM concentrations (p = 0.02), which is likely an effect of human recreational activity and disturbance. There was no difference in uGM concentrations between failed and successful nests. Our results highlight the potential impact of road and path proximity on white-tailed sea eagles, with potential importance for species management and conservation, particularly with respect to nest protection zone legislation.