BEHAVIOR EFFECTS OF LEAD-EXPOSURE ON DIFFERENT DAYS FOR GULL (LARUS-ARGENTATUS) CHICKS

Lead exposure early in life affects behavioral, physiologic, and intellectual development in humans and other animals. In this article, we examine the effects of temporal differences in lead exposure on early development in herring gulls (Larus argentatus). Each of 72 1-day-old herring gull chicks was randomly assigned to one of six treatment groups to receive a lead nitrate concentration of 100 mu g/g at age 2 or at age 6, a similar cumulative dose evenly divided on days 2, 4, and 6, or matched-volume saline injections on the same days. Behavioral tests were performed (some at 2- and others at 5-day intervals) to examine locomotion, balance, righting response, thermoregulation, and visual cliff. Most variation in weight was explained by testing age, although treatment affected weight gain for the lead-6 gulls, particularly after 20 days. Although treatment influenced balance and locomotion, the effect was small. The lead-6 birds were unable to remain on an incline as long as the lead-2, lead-246, and control birds. The overall score for balance improved with age for controls, showed little change for the lead-2 and lead-2-4-6 gulls, but showed a decrease in performance for the lead-6 birds. On the thermoregulation test, the lead-6 birds performed less well under both low- and high-temperature test conditions. Although the lead-2-4-6 birds had a lower score on the visual cliff tests than the other groups, the lead-6 gulls showed a significant delay in response and gave significantly fewer calls then the other groups. Overall, the data showed that the lead-6 group was more affected by the dose than the other groups, suggesting that 6 days of age may be a more critical period than earlier ages for some behaviors.