Otherwise, the effects of oil spills on the pigeon guillemot are unclear. Avian predation is the most common cause of egg loss in the pigeon guillemot. Bald eagles and pigeon guillemot are frequently in the park as well. The pigeon guillemot and the black guillemot form a superspecies. The pigeon guillemot walks well and habitually has an upright posture. In the spring and summer pigeon guillemot and Leach's storm petrel nest on the island. The pigeon guillemot is a medium-sized auk, in length and weighing . The pigeon guillemot ("Cepphus columba") is a species of bird in the auk family, Alcidae.