Abstract
Lead is ubiquitous in nature, and can affect behavioral, physiological, and intellectual development in humans and other animals. We used lead-induced behavioral deficits to examine the behavior of parents and young herring gulls in the Captree, NY, gull colony. Our objectives were to determine: a) If there were differences in the behavior, weight, and survival of chicks as a function of treatment; b) if parental behavior varied as a function of treatment; and 3) if there were differences in sibling competition and parent-young conflict between experimental nests (with lead-impaired chicks and control chicks) and control nests. We injected one chick in each of 22 nests (1–2 days of age) with lead acetate (100 mg/kg in sterile water) and injected its sibling with sterile saline, and compared behavior of parents and young (from 1–21 days postinjection). We also observed behavior of parents and chicks in 12 control nests in which chicks were handled similarly but were not injected. There were significant lead-induced differences in righting response, locomotion, thermoregulation, begging, and feeding behavior in the chicks; corroborating observations from the laboratory. Lead-injected chicks were less able to compete for food with their siblings, with a resultant significant difference by weight at 16 days of age. For experimental nests in which the weight difference was great, parents engaged in divided feeding of the brood. After one parent initiated feeding, the other parent walked a short distance away and began to call to and then feed the second, smaller chick. The extra parental care resulted in increased survival for the lead-injected chicks, and in their catching up to their siblings in weight by fledging. The results of this experiment indicate that lead induces behavioral deficits and growth retardation in gulls in nature, decreases survival at young ages, and that parents compensate for these behavioral and growth deficits by brood division for feeding chicks such that by fledging the chicks are no longer at a weight and size disadvantage. Parents are, thus, able to perceive a difference in body size and/or vigor of their offspring, and to behaviorally compensate partially for the lead-induced deficits.