Effects of Lead on Learning in Herring Gulls: An Avian Wildlife Model for Neurobehavioral Deficits

Lead is one of the most common metals in contaminated ecosystems. Although lead poisoning and mortality have long been known, little is known of the neurobehavioral effects produced by low levels of lead in wild animals. Herein we describe the neurobehavioral effects of lead on learning using herring gulls (Larus argentatus) as a model. Doses used in these studies conducted in the laboratory and in nature were sufficient to produce lead concentrations in feathers that were equivalent to those found in gulls living in the wild. The exposure consisted of a single intraperitoneal injection of 0 and 100 mg/kg lead acetate on day 2; each experiment involved 20-30 chicks in a lead-exposed group, and 20-30 chicks in a control group. We examined walking, begging, feeding, behavioral thermoregulation, individual recognition, and treadmill learning. There were significant differences between control and lead-exposed gulls chicks on all testing days. Learning, as well as improvement of motor skills, was faster for control chicks than lead-injected chicks for the thermoregulatory test, individual recognition, and behavior on a treadmill. Lead-injected chicks improved faster than control chicks only for walking scores. In a test where chicks were shown food under a cup, and then tested with three overturned cups, lead-exposed chicks did not show much improvement, whereas control chicks quickly learned where the food was located. The greatest differences in improvement were on the behavioral thermoregulation test, where lead-exposed chicks showed no improvement with age. Overall, this series of experiments indicated that for tasks involving learning, the disparity in accuracy and ability remained regardless of the number of days since exposure-control chicks sometimes improved and learned quicker than did lead-exposed chicks.