Abstract
Animals are exposed to a wide range of human-induced changes in their environment, as well as to chemicals that are harmful. Birds, such as Herring Gull, can serve as models for scientists to understand how changes in habitat and chemicals can affect the behavior, physiology, and reproductive success of species and of the ecosystems they inhabit. Herring Gulls are ideal bioindicators because they are common, widespread, and indicative of the potential effects of chemicals and habitat destruction on birds. Both natural and anthropogenic factors can determine where Herring Gulls nest, as well as the timing of nesting and reproductive success. Territory size varies in the gulls, with those defending intermediate-sized territories engaging in aggression less often and raising more young ones than birds that are more highly aggressive and defend larger territories. Laboratory and field experiments indicate that Herring Gulls are good bioindicators of the effect of chemicals on behavior. Gulls exposed to lead and other chemicals exhibited a wide range of behavioral deficits in their growth, ability to walk, balance, forage, and recognize their parents and siblings. In nature, these behaviors can (and did) lower reproductive success.