Rhinoceros auklets are seabirds that live along the Pacific coast of North America. They are found from the Aleutian Islands and Gulf of Alaska south to Baja California, Mexico. Their breeding habitat is on offshore islands, rocky headlands, and sea stacks along this coastline. Rhinoceros auklets nest in burrows or rock crevices and only come to land during the breeding season. The rest of the year they live exclusively at sea.
Range and Distribution
The rhinoceros auklet has a large range along the Pacific coast of North America. Their breeding range extends from the western Aleutian Islands in Alaska south to Islas San Benito in Baja California, Mexico. Here are some more details on where they breed and can be found:
- Alaska – They breed along the Aleutian Islands, the Alaska Peninsula, and other offshore islands in the Gulf of Alaska south to Forrester Island.
- British Columbia – They breed on the Queen Charlotte Islands and other coastal islands. Major breeding sites include Pine and Lucy Islands.
- Washington – Major breeding sites include Destruction Island, Smith Island, and Protection Island.
- Oregon – Important breeding colonies occur on Three Arch Rocks, Haystack Rock, and Face Rock.
- California – They breed on the Farallon Islands, Año Nuevo Island, and Castle Rock. Other breeding sites scattered along the coast south to Mexico.
During the nonbreeding season, rhinoceros auklets are highly pelagic. They range along the continental shelf from Alaska to Baja California, Mexico. They are most abundant within 50 miles of shore. Their range extends farther offshore in winter months when prey is less available in nearshore waters.
Habitat
Rhinoceros auklets nest on remote offshore islands and rocks. They require islands free of terrestrial predators. Breeding sites are typically covered with grassy vegetation. Burrow sites are often on steep slopes with friable soils. Their colonial breeding sites are highly clustered.
At sea, rhinoceros auklets forage over continental shelf waters. They mainly occur over shallow waters less than 200 feet deep. Productive upwelling zones with lots of bait fish are important marine habitat. They also feed near kelp forests, seamounts, and oceanic fronts that congregate prey.
Population and Conservation
The global population of rhinoceros auklets is estimated at 1.1 million breeding birds. About 405,000 pairs breed in British Columbia and 420,000 pairs in Alaska. Here is a table showing population estimates by region:
Region | Estimated Population |
---|---|
British Columbia | 405,000 pairs |
Washington | 4,000 pairs |
Oregon | 25,000 pairs |
California | 15,000 pairs |
Alaska | 420,000 pairs |
Russia | 2,800 pairs |
Japan | 5,500 pairs |
Mexico | 2,000 pairs |
Rhinoceros auklet populations declined in the late 19th and early 20th centuries due to hunting for feathers and eggs. Their numbers rebounded after protections were enacted. Today their global population is estimated to be increasing. However, oil spills and habitat loss remain threats. Conservation efforts are aimed at protecting breeding colonies from disturbance and preventing oil spills in foraging habitat.
Key Facts
- Rhinoceros auklets are medium-sized seabirds in the family Alcidae.
- Their breeding habitat extends along the Pacific coast from the Aleutians to Baja California.
- They nest colonially in burrows on remote offshore islands and rocks.
- During the nonbreeding season they are highly pelagic, ranging widely over continental shelf waters.
- They forage on small fish, crustaceans, and other marine invertebrates.
- The global population is estimated at 1.1 million breeding birds and is increasing overall.
- Major threats include oil spills, human disturbance, and habitat loss.
Appearance and Size
Rhinoceros auklets are medium-sized seabirds, averaging about 33 cm (13 in) long and weighing around 535 g (1.2 lb). Here are some key facts about their appearance and size:
- They have a large puffin-like bill that is vertically grooved and has a horn-like projection at the base, giving them their common name.
- Their plumage is dark gray above and pale gray below. Their underparts vary from white to gray.
- During breeding season, adults have white “horn” plumes above their eyes.
- Their legs and feet are orangish pink with claws for grasping ledges and crevices.
- Males and females look alike. Females are slightly larger than males on average.
- Juveniles have drabber plumage overall and lack the white “horn” plumes.
Their unique rhinoceros-like bill easily distinguishes them from other auklet species. It is also used for displaying during the breeding season. Their plumage is well-adapted for life at sea, allowing them to camouflage and shed water easily as they swim and dive.
Diet and Feeding
Rhinoceros auklets are carnivorous and feed on small marine organisms. Their diet consists mainly of fish, crustaceans, and other invertebrates. Here are some details on what they eat:
- Fish – Small fish like anchovies, herring, and sandlance make up over 50% of their diet. They also eat rockfish, surfperch, and salmon.
- Crustaceans – Krill, amphipods, crab larvae are regularly consumed.
- Cephalopods – Squid are an important food source during winter months.
- Other – They also prey on polychaete worms, mollusks, and jellyfish when available.
Rhinoceros auklets are pursuit divers that catch prey underwater. They typically dive to depths of 130-200 ft to find food but can dive up to 240 ft. Their flexible wings allow them to “fly” underwater. They can hold their breath for over a minute while diving. Parents feed chicks by carrying prey back in their bill.
Breeding and Nesting
Rhinoceros auklets nest in colonies on remote offshore islands and rocks. Here are some key facts about their breeding and nesting habits:
- Breeding season lasts from April to September, peaking in June-August.
- They nest in burrows dug in soil or rock crevices. Nest sites are often lined with vegetation, feathers, or debris.
- Colonial nesting areas can have up to 15-25 nesting pairs per 100 square meters.
- Females lay a single egg per season. Eggs are pale blue-green with brown markings.
- Both parents incubate the egg for about 50 days until it hatches. Chicks fledge after 45-55 days.
- Parents feed the chick by carrying fish back in their bill. Chicks are fed an average of 6 times per day.
- Chicks are semiprecocial at hatching but rely on parents for warmth, protection, and food.
Rhinoceros auklets exhibit high nest site fidelity. Pairs often return to the same burrow year after year. Colony attendance is lowest during winter months when birds disperse farther offshore.
Behavior and Sociality
Here are some key facts about the behavior and social habits of rhinoceros auklets:
- They are colonial nesters and breed in aggregations of hundreds to thousands of pairs.
- They are mostly silent at sea but vocalize with barks, grunts, and groans at breeding colonies.
- Their courtship displays include upright posture, bill pointing, and mutual billing between mates.
- They are monogamous and likely mate for life. Partners reinforce their bond with duetting calls.
- Outside of breeding season they are highly pelagic and spend little time on land.
- They are strong fliers and use their wings to “fly” underwater as they dive in pursuit of prey.
- They are highly gregarious at sea and form large multi-species feeding flocks.
Rhinoceros auklets have elaborate social behaviors and displays during breeding season. Their colonies are very noisy as they groan, bark, and bill-clap to claim nest sites and attract mates. Pairs reinforce lifelong bonds through synchronized calls and mutual billing.
Migration and Movement
Rhinoceros auklets exhibit seasonal migration patterns influenced by breeding and availability of prey. Here are some key facts about their migratory habits:
- They arrive at breeding colonies in early spring, typically March-April.
- Most birds depart colonies by late fall, dispersing offshore and south along the coast.
- Northern populations show more extensive winter migrations compared to southern birds.
- Alaska breeders migrate south to winter off British Columbia, Washington, and Oregon.
- Birds banded in California have been observed migrating as far north as Alaska.
- Young birds tend to travel farther than adults during winter dispersal periods.
Rhinoceros auklets are highly pelagic outside the breeding season. Their winter movements and habitat use are likely driven by the distribution and abundance of prey like anchovies, herring, and krill.
Conclusion
In summary, rhinoceros auklets are seabirds of the Pacific coast of North America. Their breeding habitat extends from the Aleutian Islands to Baja California, Mexico. They nest colonially on remote offshore islands and rocky outcrops. During the nonbreeding season they are highly pelagic, dispersing widely along the continental shelf. Rhinoceros auklets are pursuit divers that prey on fish, crustaceans, and other marine organisms. They are social birds that breed in dense colonies. Their populations are estimated at over 1 million birds globally and appear to be increasing in most regions.