Birds exposed to polychlorinated biphenyls (PCBs) as nestlings show behavior changes as adults. These changes can include decreased fear of predators, increased aggression, and impaired social interactions. PCBs are a group of man-made chemicals that were widely used in industry until they were banned in many countries due to their environmental persistence and toxicity. PCBs can be transported through the air, water, and soil, and they can accumulate in the tissues of animals, including birds.

Studies have shown that exposure to PCBs during development can have lasting effects on the brain and behavior of birds. For example, one study found that herring gull chicks exposed to PCBs as nestlings showed decreased fear of predators and increased boldness in adulthood. Another study found that male zebra finches exposed to PCBs as nestlings were more aggressive than unexposed males, and they had impaired social interactions with females.

The behavioral changes seen in birds exposed to PCBs are thought to be caused by the disruption of the endocrine system. PCBs can interfere with the production and function of hormones, which can have a variety of effects on the brain and behavior. For example, PCBs can decrease the production of thyroid hormone, which can lead to decreased fear of predators and increased boldness. PCBs can also increase the production of estrogen, which can lead to increased aggression in males.

The behavioral changes seen in birds exposed to PCBs can have a negative impact on their survival and reproduction. For example, birds that are less fearful of predators may be more likely to be killed by predators. Birds that are more aggressive may be less successful at finding mates and raising young. The behavioral changes seen in birds exposed to PCBs are a reminder of the importance of protecting the environment from harmful chemicals.