ABSTRACT
This chapter examines four specific examples of studies in wild birds, the role of the sexual cycle in the modification of MFO activity and consequently the importance of considering this aspect in planning biomonitoring. The four examples are the seasonal variations in the activity of hepatic aldrin epoxidase in a population of wood pigeon (Columba palumbus) in a relatively unpolluted area of central Italy, the seasonal variation of the same enzyme in the yellow-legged herring gull (Larus argentatus cachinnans) from northern Italy, changes in the activity of several MFO enzymes during the breeding cycle of the herring gull (Larus argentatus smithsonianus) and a comparison with activity found during the winter in Eastern Canada, and the different levels of aldrin epoxidase activities and PCB concentrations in the liver of the yellow-legged herring gull collected during the reproductive and post-reproductive periods in several polluted areas of Italy.
