The rhinoceros auklet (Cerorhinca monocerata) is a fascinating seabird found along the Pacific coast of North America. With its large orange bill that resembles a rhinoceros horn, the rhinoceros auklet stands out among other seabirds. This distinctive-looking bird has many interesting characteristics related to its appearance, distribution, habitat, diet, breeding, and conservation status. Keep reading to learn more about what makes the rhinoceros auklet unique!
Quick Facts
- Scientific Name: Cerorhinca monocerata
- Other Common Names: Horn-billed puffin, unicorn puffin
- Size: 28-33 cm (11-13 in) long with 50 cm (20 in) wingspan
- Weight: 350-500 g (12-18 oz)
- Lifespan: Up to 18 years in wild
- Conservation Status: Least Concern
Appearance
The most distinctive feature of the rhinoceros auklet is its large, heavy orange bill that is flattened at the sides. The bill is broad and deep, curving slightly upwards to end in a point. Small backward-facing serrations line the cutting edges of the bill, which is also encircled by an orange-yellow gape. During breeding season, the bill becomes brighter orange with an obvious knob at the base. This knob inspired the alternate name “unicorn puffin”.
Rhinoceros auklets have slate-gray bodies and wings with white undersides. Their short necks and rounded heads lack an obvious crest. Legs and feet are pinkish with black webbing between the toes. Their eyes are brown-gray. Males and females look identical. Juvenile birds have smaller grayish-brown bills, darker plumage, and paler legs.
Overall, rhinoceros auklets are stocky, chunky seabirds. Their thickset bodies, short necks, and large bill give them a distinctive profile in flight and while swimming and diving.
Distribution
The rhinoceros auklet has a narrow distribution along the Pacific coast of North America. Their breeding range extends from the Aleutian Islands in Alaska down to Baja California in Mexico. Major nesting sites are located on offshore islands and rocks along British Columbia, Washington, Oregon, and California.
Outside of breeding season, rhinoceros auklets disperse somewhat further offshore and south to central Baja California. However, most birds do not migrate long distances and remain near their breeding sites year-round.
A closely related subspecies called the Japanese rhinoceros auklet is found in Japan and Russia. The ranges of the two subspecies do not overlap across the northern Pacific Ocean.
Habitat
Rhinoceros auklets nest on small, remote islands with grassy slopes. They choose islands that are too small or distant for most mammals to colonize. This reduces predation risk since rhinoceros auklets are highly vulnerable while nesting on the ground.
Ideal habitat provides crevices in rocks, cracks in boulders, or small caves for nesting. Rhinoceros auklets do not dig burrows and rely on natural cavities. Grass, shrubs, or other vegetation is necessary to conceal the nest entrance.
At sea, rhinoceros auklets frequent inshore waters over continental shelves and around islands. They forage in shallow bays, channels, and kelp beds usually within 20 km (12 mi) of shore. Rhinoceros auklets occasionally visit more pelagic waters further offshore.
Diet
Rhinoceros auklets mainly eat small fish, marine invertebrates, and some plankton. Their diet consists of:
- Small schooling fish like herring, anchovies, and sandlance
- Crustaceans including euphausiids (krill), crab larvae, copepods
- Mollusks such as squid and small octopus
- Worms and other soft-bodied invertebrates
They capture prey while swimming and diving underwater. Most foraging occurs at depths less than 25 m (80 ft). Rhinoceros auklets use their large bills to grasp and manipulate prey. Unlike other puffins, they do not carry multiple prey crosswise in their bill.
Parents feed chicks primarily fish like Pacific sandlance, rockfish, and salmon. Adults swallow plankton and small crustaceans themselves before regurgitating the partially digested contents for the chicks.
Breeding
The breeding season for rhinoceros auklets extends from April to August depending on latitude. Most birds first breed when 3-5 years old.
Rhinoceros auklets are colonial nesters, breeding in aggregations of up to 9,000 pairs. However, small groups of 10-100 pairs are more typical on smaller islands. Nests are spaced 1-4 m (3-13 ft) apart.
Courtship consists of flying, swimming, and diving displays. Males make trumpeting calls to attract females. Once paired, the male and female groom and call to each other while standing upright with bills pointed skyward.
Pairs usually mate for life. They nest in rock crevices, cracks, small caves, and under vegetation. Both adults help excavate the nest but males perform most of the excavation over 2-14 days. Nests consist of a scraped depression lined with a few twigs, grass, and feathers.
Females lay a single egg per season. Eggs are buff colored with brown spotting. Parents share incubation duties for 39-49 days until the egg hatches.
Chicks have black downy feathers at hatching. Both parents feed the chick through regurgitation. Chicks fledge at 45-55 days old but may return to the nest briefly for additional care. Parents continue to feed independent juveniles at sea for several months.
Breeding Challenges
Breeding rhinoceros auklets face threats from habitat loss, introduced predators, human disturbance, and climate change. Degrading nesting habitat and predation reduce reproductive success.
On breeding islands, rhinoceros auklets are highly vulnerable to disturbance. When flushed off their nests, the eggs and chicks may overheat or freeze. Adult birds can also collide with structures and become disoriented.
Conservation Status
The global population of rhinoceros auklets is estimated at 1.5-2.2 million mature adults. Global trends are decreasing but the decline is small enough that IUCN Red List classifies the rhinoceros auklet as a species of Least Concern.
However, some local subpopulations are declining more significantly. The largest threats rhinoceros auklets face are:
- Invasive species like rats, raccoons, and foxes on breeding islands
- Disturbance from human activity near breeding colonies
- Entanglement in fishing nets and hooks
- Oil spills
- Reduced prey availability due to overfishing and climate shifts
Conservation actions needed include protecting and managing breeding sites, controlling invasive predators, monitoring subpopulations, and reducing offshore threats. With proper management, the outlook for rhinoceros auklet populations can improve.
Fun Facts
Here are a few fun and interesting facts about the charismatic rhinoceros auklet:
- Rhinoceros auklets stuff prey down their throat whole. Their throat pouch can stretch to hold 20-30 fish!
- They are very social and vocal. Groups of courting birds chatter, trumpeting, and grunt outside their burrow.
- Males use a scented powder made by a breast gland to attract females.
- Chicks beg for food by poking their bill in the parent’s mouth and rattling it.
- Rhinoceros auklets have been recorded diving as deep as 72 m (236 ft).
- They are clumsy on land but incredibly agile underwater.
Conclusion
In summary, rhinoceros auklets are highly adapted seabirds of the Pacific Coast. Their unique large bill aids feeding and gives them a one-of-a-kind appearance. Breeding in large colonies on remote islands, rhinoceros auklets work together to excavate nest sites and raise their young. Though global populations are currently stable, local declines make persistent conservation efforts necessary, especially protection of breeding colonies from human disturbance. With a fascinating lifestyle and appearance, the rhinoceros auklet remains a cherished seabird along the Pacific shores.