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Cerorhinca monocerata - Rhinoceros Auklet

Rhinoceros Auklet image

Geographic range:

Northern Pacific Ocean

Key features:

Coloration is dark gray except for white belly. Breeding adult displays a vertical white line at base of orange bill and two white plumes on face.

Similar species:

Fratercula cirrhata -- Tufted puffin
Fratercula corniculata -- Horned puffin


bay (rocky shore), bay (sandy shore), exposed rocky shore, pelagic zone, protected rocky shore, protected sandy beaches

Primary common name:

Rhinoceros Auklet

General grouping:

Seabirds and shorebirds

ITIS code:


Geographic Range

Range Description:

Cerorhinca monocerata ranges widely across the North Pacific and in North American occupy breeding territory from the Channel Islands, California to the Aleutian Islands, Alaska. In Asia, it occupies breeding territory in Hokkaido and Honshu, Japan as well as North Korea and Sakhalin Island.


bay (rocky shore), bay (sandy shore), exposed rocky shore, pelagic zone, protected rocky shore, protected sandy beaches

Habitat notes:

Cerorhinca monocerata is a pelagic species, and while it ranges quite far seaward, it can be seen from shore and found in coastal habitats. Flocks of Cerorhinca monocerata will over over-night in protected bays and forage farther out to sea during the day. Therefore, Cerorhinca monocerata can often be seen in large numbers close inshore. Nesting islands typically have grass, shrubs or trees and enough soil for the birds to burrow.


Relative abundance:

Cerorhinca monocerata is common along most of the West coast in late fall and early spring, but are only occasionally abundant in winter. This species is generally more common and widely distributed off Northern California than Southern California.

Species Description

General description:

Cerorhinca monocerata is a medium to large sized auk with a large, strong, orange/brown bill with a horn protruding from it. The name of this bird is derived from this horn-like extension of the beak, which is only present in breeding adults, and is shed every year. Cerorhinca monocerata is a dark puffin-like alcid with a whitish belly, which shows only in flight.

Distinctive features:

Cerorhinca monocerata has a dark gray head with coppery iridescence on the neck. The body is drab gray above, but paler on the sides, neck and throat. In flight, the whitish belly blends into the dark breast and can be distinguished from the similar Parakeet Auklet, Aethia psittacula, which has extensively white underparts. The body is pale gray, the bill is short and black and the legs are short and red. Variations range from black to pale brown and white. Cerorhinca monocerata is larger and darker than Cassinís auklet,Ptychoramphus aleuticus, or other murrelets, and the closely related, but rarer, Tufted Puffin, Fratercula cirrhata is the only real look-alike.

In breeding plumage, Cerorhinca monocerata has two distinct white plumes on the head and an orange-yellow bill adorned with a whitish horn and a yellow iris. Winter adults are similar, but lack the horn and plumes. Juveniles appear similar to the non-breeding adult, lacking both the feather tufts and beak horn. They are also more blackish around the head and many have thinner and darker bills and dark irises.


Cerorhinca monocerata can grow to a length of 38 cm with a wingspan of 62 cm.

Natural History

General natural history:

Cerorhinca monocerata belongs to the family Alcidae; Puffins and Murres are in this same family. It is the only member of its genus. Cerorhinca monocerata is an excellent diver and swims underwater using its wings like flippers. Dives can last up to two minutes. The behavior on Cerorhinca monocerata on land has been difficult to observe because they are nocturnal at their nesting colonies. This nocturnal behavior is believed to be a response to predation and kleptoparasitism by gulls. Kleptoparasitism is a form of feeding where one animal takes prey from another that has caught, killed, or otherwise prepared it, including stored food provisions.


Rodents may prey on Cerorhinca monocerata\\\\\\\\\\\\\\\'s eggs during the breeding season.


At sea, Cerorhinca monocerata feeds mostly on small fish, but krill and squid can also be eaten. During the breeding season, they feed inshore, again mostly on small fish.

Feeding behavior


Feeding behavior notes:

Cerorhinca monocerata usually feeds close to shore, especially where tidal currents near islands create upwellings and concentrations of food.

December - February


Cerorhinca monocerata is more migratory than most western alcids, but there is still considerable overlap between summer and winter ranges. It will winter both in offshore and inshore waters.

June - August


Cerorhinca monocerata breeds during the summer season. It will nest in burrows dug in the ground or in natural caves and cavities. Burrows can be up to six and a half meters long and often fork many times and can occur on both forested and non-forested islands. At the end of each burrow is a nest chamber with a shallow cup of moss and twigs. Cerorhinca monocerata prefers nesting sites on slight inclines to aid take-off. The female will lay one egg, and both parents will incubate it for five and a half to seven and a half weeks. Both parents will feed the chick with a bill full of fish for about seven or eight weeks, after which time, the chick leaves the nest.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Alden, P., F. Heath, R. Keen, A. Leventer, and W. Zomlefer. 2002. National Audubon Society Field Guide to California. A.A. Knopf, New York, NY.
Blight, L.K., J.L. Ryder, and D.F. Bertram. 1999. Predation on Rhinoceros auklet eggs by a native population of Peromyscus. Condor 101: 871-876.
Dunn, J.L. 1999. Birds of North America. National Geographic, Washington, D.C. 464 p.
Stallcup, R. 1990. Ocean Birds of the Nearshore Pacific. Point Reyes Bird Observatory, Stinson Beach, CA. 214 p.
Cornell Lab of Ornithology
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