Rhinoceros Auklet (Cerorhinca monocerata) 



World Breeding Range 



The Rhinoceros Auklet is an uncommon 

 breeding seabird in California. It derives its name 

 from the keratinous "horn" found on its bill 

 during the breeding season. Although this species' 

 common name implies it is an auklet, the 

 Rhinoceros Auklet is more closely related to the 

 puffins. Rhinoceros Auklets are excellent divers 

 and feed on small fish and cephalopods (Heath 

 1915, Richardson 1961, Leschner 1976). 



Rhinoceros Auklets nest primarily in burrows 

 dug into the ground on both forested and un- 

 forested islands. Burrows may be up to 6 meters 

 in length and often fork two or three times before 

 ending in a nesting cavity (Heath 1915, Willett 

 1915). The recent discovery of Rhinoceros 

 Auklets at Sea Lion Caves, Oregon (Scott et al. 

 1974, Varoujean and Pitman 1980) and at caves in 

 the conglomerate cliffs at Point Arguello (501 

 010) indicates that this species may also nest in 

 rocky mainland habitats. 



Rhinoceros Auklets almost always enter and 

 leave colonies at night when feeding chicks. This 

 predominantly nocturnal behavior may have 

 evolved as a means to reduce kleptoparasitism by 

 gulls. In California and Oregon, Rhinoceros 

 Auklets can often be observed on or near colonies 

 during the day, but farther north they appear to 

 be strictly nocturnal. This difference remains 

 unexplained but may be related to the availability 

 of food and its proximity to the colonies. Despite 

 their diurnal tendencies in California, Rhinoceros 

 Auklet colonies are some of the most difficult to 

 find and census of all colonies of breeding seabird s 

 in the state. 



CALIFORNIA COLONIES 



Rhinoceros Auklets are known from eight 

 sites in California, but breeding has been confirmed 

 at only three: Prince Island (325 003), Castle 

 Rock (325 006), and the Farallon Islands (429 

 012). At the remaining five sites we have observed 

 Rhinoceros Auklets in breeding plumage on or 

 near the colony and suspect breeding occurs. 

 Small numbers of Rhinoceros Auklets likely 

 occur at several more sites, particularly in northern 

 California. 



Up to five birds were seen on Green Rock 

 (325 020) at one time and birds were observed 

 entering burrows on several occasions. As many 

 as 38 Rhinoceros Auklets have been seen in the 

 water next to or flying in the vicinity of Green 

 Rock at one time. Rhinoceros Auklets have been 

 suspected to breed at this site for several years 

 (LeValley pers. comm.). At Gualala Point Island 

 (404 004), Fish Rock (404 003), and Arched 

 Rock (404 006), the presence of birds on the 

 water immediately adjacent to the rock or doing 

 "fly-by's", and the presence of suitable burrows, 

 strongly suggests breeding at these sites. Rhinoc- 

 eros Auklets are also suspected to breed at 

 Little River Rock (325 035); (Harris pers. comm.). 



Point Arguello (501 010) may support a 

 mainland colony of breeding Rhinoceros Auklets 

 in California. We observed a maximum of 24 

 birds on 1 1 June 1980. A minimum of 13 birds 

 were discovered entering and leaving small caves 

 in the cliffs on 17 and 18 July 1980. An examin- 

 ation of these caves was inconclusive. 



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