Rhinoceros Auklet

Bird of the Month: Rhinoceros Auklet

By Andrew McCormick

PC: Mick Thompson (Rhinoceros Auklet)

PC: Mick Thompson (Rhinoceros Auklet)

Scientific Name: Cerorhinca monocerata

Length 15" long

Wingspan 22"

Weight 1.1 lb

AOU Band code RHAU

The Rhinoceros Auklet is named for the horn at the base of its bill.  It is in the genus cerorhinca (horn-nose) from the Greek keras, horn, and rugkhos, snout.  Rhinoceros is made up of the same two Greek elements which are reversed.   Auklet, a little auk, is derived from the Old Norse alka, which refers to a number of northern birds (Holloway).

With its dark gray head and dark back and chest the Rhino can be difficult to see on the water.  Fortunately, its angular head and heavy, yellow-orange bill provide a distinctive silhouette.  Its belly and undertail coverts are a dull white.  In breeding season the horn is whitish and prominent at the base of the bill but it sheds by fall.  Also impressive during breeding are the two sets of white facial plumes.  These however fade in winter.  Most of the Rhinos in Washington waters winter at sea but individual birds can often be seen in Puget Sound.  The birds make mooing and coughing sounds on the breeding grounds, but at other times of year are fairly silent.

In March and April, Rhinos head to their island nesting colonies primarily along the coast of British Columbia and Southeast Alaska.  Smaller numbers nest on the Farallon Islands off California and on Protection Island, WA.  The birds construct a shallow nest lined with moss and twigs in a side chamber of a burrow which they have dug 5-10 feet into a grassy or wooded hillside.   A single egg is incubated by both parents for 40-50 days and the young bird leaves the nest in another two months.  Rhinos are the only auklets that are nocturnal feeders.   Scientists think this is a new behavior in response to kleptoparasitism by gulls and attacks by Bald Eagles which hunt for auklets on the breeding sites (Gaston and Dechesne).  The bird has a distinctive but poorly studied mechanism for herding fish such as sand lance and herring by emitting bubble trails which seem to prevent the schools from breaking up.  They are able to capture fish while holding others in their bill and are able to return a “bill load” of one to several fish back to the nest (Gaston and Dechesne).

Rhino populations are stable but can be at risk to local predators in the burrows because of their low birth rate.  This is partially balanced by a greater opportunity to breed during their long life span which can reach 25 years (Sibley).  Conservation efforts have been successful.  Eradication of raccoons (British Columbia), foxes (Alaska) and rabbits (California) has allowed Rhinos to reestablish their colonies.  In 1968 sheep were removed from Protection Island and the number of burrows rose from 3,500 to 28,000 by 1974 (Gaston and Dechesne).  The Rhinoceros Auklet is a small bird on a big ocean, so look for them on Puget Sound.