Abstract
Lead exposure early in life affects behavioral, physiological, and intellectual development in humans and other animals. Recognition of parents or other caregivers and eventual bonding are essential aspects of behavioral development. In this paper young herring gulls, Larus argentatus, were used to examine the effect of timing of lead exposure on individual recognition behavior and development. Each of 60 1-day-old herring gull chicks was randomly assigned to a control group or to one of three treatment groups that received a single dose of lead nitrate solution (100 mg/kg) at Day 2 or 6 of age or the same total dose divided in thirds on Day 2, 4, and 6. Matched controls were injected with isotonic saline on the same schedules. Variations in individual recognition of human attendants were largely explained by age and status (lead versus control), and some variation was explained by day of injection (exposure regime). Using a feeding paradigm, the percentage responding to their caretaker compared to another person was higher (70% versus 38%), and occurred earlier in controls compared to lead-injected birds. Lead-injected birds required longer to respond initially, took longer to choose, moved less distance per time, and took longer to eventually reach the food. These results were all significant by GLM models and Kruskal-Wallis tests. Among lead-injected birds there was a disjunction of effect related to dosing schedule: birds injected on Day 6 chose more correctly but were slower to respond, indicating that these behavioral traits were differently affected by timing of exposure. These data suggest that there is a critical period during development when individual recognition can be disrupted by lead.