When a wild bird is stressed, their body releases a hormone called corticosterone. This hormone helps the bird to cope with stress by making its heart beat faster, its blood pressure goes up, and its blood sugar levels go up. They may become more aggressive, more careful, or more noisy. These changes help the bird avoid predators, find food, and protect their young. Their heart rate and blood pressure may go up, and their digestive system may slow down. These changes help the bird conserve energy and to focus on dealing with the stressor.