Return of Bird of the Week: Rhinoceros Auklet

Rhinoceros Auklet in breeding plumage, Prince William Sound, Alaska

The Brits use the term “confiding” to describe a bird or bird species that is more approachable than most. In WC’s admittedly small experience, the Rhinoceros Auklet is the most approachable alcid. Aboard the auspiciously named R/V Auklet, piloted By the delightful David Lanka (since retired), we were able to approach with 10 feet of a small, loafing flock of Rhinoceros Auklets. So far as is known there are no breeding colonies of the species in Prince William Sound. So these were either subadults, not yet ready to mate, or a flock en route to a colony.

The species’ common name comes from the small, horn-like protuberance on their upper bill. It’s actually a vertical extension of the mandibular plates, largest in breeding season, displayed by both sexes. Its function is unknown and, to WC, it doesn’t look much like a rhinoceros horn.

Rhinoceros Auklet, Alaska Sealife Center, Seward, Alaska (semi-captive bird)

Unlike earlier auklets posted here, this species is rarely seen in the Bering Sea; it’s a somewhat more southerly species, found across the continental shelf waters of the North Pacific, from Japan to California. WC has seen it, from a distance, off Monterey Bay, California. It’s also a mostly nocturnal species, which is believed to be an adaption to minimize predation and kleptoparasitism by gulls and raptors.

Post-breeding plumage Rhinoceros Auklet, Monterey Bay, California (heavy crop)

Rhinoceros Auklets forage nearer shore than their other alcid cousins, mostly in depths of 20 meters or less. While there is good data for what is fed to chicks, adults’ diet is less well described. It appears to consist mostly of midwater schooling fishes, particularly sandlance, anchovies and juvenile rockfish. Based on the bite marks on fish presented to hatchlings, prey fish are caught from behind, by pursuit and not ambush.

This is a colonial, burrowing nesting species. Burrows are about 0.5 to 1 meter apart, and 1 to 5 meters long. Burrows are excavated among dense ground vegetation, especially in grass tussocks, or beneath forest, mainly on grassy slopes. The nest itself is lined with vegetation or leaf litter. There is a single egg, incubated by both parents. Incubation is 39 – 52 days, and is not always continuous. Most incubation shifts are 24 hours, but occasionally, where a parent has to go a long ways to forage, may last up to 4 days, with longer shifts tending to be earlier in incubation.

Hatchlings are fed by both parents. This species’ bills, like puffins, permit them to carry a fish and still catch another. Because this is primarily a nocturnal hunting and feeding species, data on foraging and chick feeding is scarce.

Hatchlings fledge in 38-56 days. Like most other alcids, once the kid leaves the nest, he or she is on her own; parents do not feed or support the fledgling.

Rhinoceros Auklet, Prince William Sound, Alaska

Population estimates of this species are only rough estimates, making worldwide population trends nearly guesses. Populations have increased significantly along the California and Oregon coasts, especially in El Niño years. But the species’ foraging habitat and behavior makes them especially susceptible to be caught and drowned in gill nets. There have also been unexplained mass die-offs in northern Japan. IUCN concluded the global population is declining, but finds them to be a species of Least Concern.

For more bird photographs, please visit WC’s bird photo site, Frozen Feather Images.

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