On a windy summer day at south Marble Island in Glacier Bay, thousands of seabirds cling to the rocks, hundreds more wheel overhead, and even more swim in the choppy water. The rocky, barren island is a well-known seabird nesting colony, and in late June, gulls, cormorants, pigeon guillemots, kittiwakes, puffins and murres are abundant.
95% of seabirds are colonial nesters, and seabird colonies offer outstanding wildlife viewing. Many seabirds show remarkable loyalty to specific colonies and exact nesting spots, returning to the same site year after year, and they will aggressively defend that site from rivals. This increases breeding success, provides a place for returning mates to reunite, and eliminates the need to prospect for a new site. Young adults breeding for the first time usually return to the colony of their birth, and often nest very close to where they hatched.
On one hand, all these nesting birds are after the same things - protection from nest predators like eagles, ravens, and otters, and access to food for themselves, their mates, and their young. But different species have different nesting needs. Puffins dig tunnels and nest underground. A female mmurre lays a single egg on a narrow rock ledge. The pointed egg, shaped like a top, rolls in a tight circle should it become dislodged. Pigeon guillemots lay two eggs and typically nest in crevices and tiny caves in the rocks. Glaucous-winged gulls generally nest in concentrated colonies, in close proximity to one another with nests commonly hidden in ryegrass or built on bedrock.