The horned puffin is a pelagic seabird that feeds primarily by diving for fish.
Horned puffins are monomorphic (the male and female exhibit the same plumage coloration). Sexually mature birds have a small fleshy black “horn” extending upwards from the eye, from which the animal derives its common name “the horned puffin”. A dark eyestripe extends backwards from the eye towards the occiput. The cheeks are white, with a yellow fleshy spot at the base of the bill.
In summer (breeding) plumage, the outer keratinous layers of the bill (rhamphotheca) grow in size and change to a bright yellow color at the base and dark orange at the tip. The size and color of the rhamphotheca helps to attract a mate. The brilliant outer layers of the rhamphotheca are shed in late summer. The face reverts to a gray and black color, with a smaller, less brilliantly colored bill, and the legs and feet fade to a pale fleshy color. This phase is referred to as eclipse plumage
Like many other seabirds, the horned puffin is countershaded for camouflage against both aerial and undersea predators. The under parts (breast, throat, belly, flanks and vent) are white, while the upper parts are black. The legs and feet are orange.