Patterns of incubation and nest-site attentiveness in relation to organochlorine (PCB) contamination in glaucous gulls

1. Although experimental studies show that organochlorines (OC) can affect bird behaviour, field assessments are invariably confounded by ecological differences between contaminated and uncontaminated sites. The behaviour of individual birds in the field has rarely been related to the contaminant burden. 2. We examined individual patterns of incubation and nest-site attentiveness in relation to OC burden, measured as polychlorinated biphenyl (PCB) concentration in the blood, of 27 glaucous gulls Larus hyperboreus in two breeding areas at Bear Island, in the north-eastern Atlantic. 3. Blood PCB concentrations ranged from 52 ng g(-1) to 1079 ng g(-1) (wet weight). There were significant differences between the two breeding areas, and females had significantly lower concentrations than males. 4. Gull behaviour differed significantly between breeding areas and sexes independently of PCB. Females incubated more than males (54% vs. 46%) but spent more time away from the nest site than males, both overall (23% vs. 12%) and when not incubating (50% vs. 21%). They were also absent for longer periods (4.5 vs. 2.8 h). Moreover, length of incubation bouts (6.4 vs. 4.4 h), the amount of time absent from the nest site when not incubating (51% vs. 25%) and length of absences (5.6 vs. 1.8 h) differed between breeding areas, probably due to different feeding specializations. 5. After controlling for these area and sex effects, the proportion of time absent from the nest site when not incubating, and the number of absences, were both significantly related to blood concentration of PCB. 6. Increased absence from the nest site in individual glaucous gulls with high blood concentrations of OC suggests effects on reproductive behaviour. We speculate that endocrine disruption or neurological effects might be involved, leading to increased energetic costs during incubation and reduced reproductive output.