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Read this excerpt from "The Day the Gulls Went Crazy" by Susan E. Quinlan.

Like most gulls, western gulls nest in colonies. This means that many pairs place their nests close together in a particular place. In contrast, most bird species place their nests in scattered, hidden locations. Colonial nesting is an unusual habit among birds because predators can easily locate nests placed close together and quickly eat many eggs and young. In general, colonial birds nest in places out of reach of predatory mammals, such as cliff ledges, river sand bars, and isolated ocean islands.

What is the author's purpose in this paragraph?