Great northern loon, Acadia National Park, 2015.

You may know the great northern loon as the common loon (Gavia immer). This adult is in non-breeding plumage, which are shades of brown with a white chin and foreneck. During breeding season the plumage changes to become the recognizably striking black head with white underparts and a checkered black-and-white mantle. Acadia has both the common loon as well as the red-throated loon. Distinguish these species by the red-throated loon's smaller and more delicate body, slender bill often pointed upward (while the common loon's bill is usually horizontal) as well as a bright, white face surrounding a dark, small eye. Amazingly, the loon has a number of solid bones, which is very unlike the normally-hollow avian bones. This extra weight aids in the loon's diving prowess but may also be one of the reasons the bird requires a long distance to gain momentum for flight take-off. Loons have the ability to dive as deep as 60 meters (200 feet) for as long as 3 minutes. Like all divers, this species is a specialist fish-eater.