The guillemot is the common name for several species of seabird in the auk family. The small arctic seabird lives on the rocky cliffs of northern coastal regions, breeding on narrow cliff ledges in dense colonies that vary in size from some hundred pairs to hundreds of thousands of pairs.

Because of the crowded conditions, hundreds of females lay their pear shaped eggs side by side on a narrow ledge, in long rows. The eggs all look alike, and yet the mother bird can identify her own eggs. Studies show that even when the eggs are moved, the mother knows her egg so well, that she will find it and return it to its original location.