Effects of Lead on Sibling Recognition in Young Herring Gulls

Abstract

Lead exposure early in life affects physiology, behavior, and cognitive development in humans and other animals. In gulls, lead also disrupts parental recognition, leading to potential decreases in survival in wild populations. In this paper, young herring gulls, Larus argentatus, were used to examine the effect of lead on sibling recognition. Each of 80 one-day-old herring gull chicks was randomly assigned to either a control group or a lead treatment group that received a single dose of lead acetate solution (100 mg/kg) at day 2. Matched controls were injected with isotonic saline at the same age. At 10 days of age, there was no demonstrable sibling recognition in control chicks, but recognition was clearly developed by 15 days of age. Lead disrupted sibling recognition, and there still was no evidence of sibling recognition in lead-injected chicks by 26 days of age. Time to respond initially increased and then decreased with age in both control and lead-injected chicks. Control chicks that correctly reached their siblings did so in significantly less time than did lead-injected chicks, and they remained closer to their siblings at the end of the test. These experiments clearly demonstrate that lead disrupts sibling recognition in herring gull chicks, delays the time to respond and to reach their siblings, and increases the final distance chicks are from their calling siblings. In nature, lead-impaired chicks would be unable to use siblings as a cue enabling them to find their nests and might suffer higher mortality from territorial adults and chicks, as well as from cannibalistic adults.