Lead levels in exposed herring gulls: differences in the field and laboratory

We compared blood lead levels for herring gull (Larus argentatus) chicks exposed at two days of age in the field and the laboratory. One randomly selected chick in each family of three was injected with lead, the second with a sterile saline solution, and the third was not injected. Field birds were then completely free-living, and were entirely cared for by their parents. Blood was drawn at 35 or 45 days of age for comparison with laboratory-reared chicks. In both the laboratory and the field, blood lead levels were positively related to dose, and concentrations were lower at 45 than at 35 days of age. However, at each dose, the field birds had lower levels than did the laboratory birds. We postulate that this relates to higher overall activity and accelerated bone development in the field, and perhaps to a move varied diet. Wild young gulls were mobile and practiced flight more often than did laboratory-reared gulls. Growth metabolic, and behavioral factors may enhance deposition of lead in the bone, reducing blood lead. Thus, both in ecological risk assessments and in using birds as bioindicators, caution is required in extrapolating from laboratory studies in field conditions.