1. Food competition: Herring gulls are opportunistic feeders and will compete with each other for food, especially during times of scarcity. When food is abundant, gulls may tolerate each other more, but when resources are limited, competition can be fierce.
2. Territory defense: Herring gulls defend their nests and breeding territories from other gulls and even different species, such as crows, ravens, and other predatory birds. They will often engage in aggressive behaviors, such as chasing, dive-bombing, and wing flapping, to try to drive off intruders.
3. Mating rights: Male herring gulls compete for the right to mate with females. Some aggressive displays include bowing, head-tossing, and loud calling. They perform these rituals to impress females and establish their dominance over other males.
4. Hierarchy: Herring gulls live in social hierarchies, with dominant individuals having priority over food and resources. They use aggressive behavior to establish and maintain their social status within the group.
5. Stress: Chronic stress from overpopulation, pollution, changes in habitat, and interactions with humans can increase the frequency of aggressive interactions among herring gulls.