Wedge-tailed shearwater
A tropical shearwater known for its wedge-shaped tail and two color morphs.
The wedge-tailed shearwater (Ardenna pacifica), known in Hawaiian as Uau Kani or Koto, is a medium-large seabird in the family Procellariidae. It is one of the shearwater species sometimes referred to as a muttonbird, found throughout the tropical Pacific and Indian Oceans between roughly latitudes 35°N and 35°S. It breeds on islands off Japan, the Islas Revillagigedo, the Hawaiian Islands, the Seychelles, the Northern Mariana Islands, and off Eastern and Western Australia.
- Scientific name
- Ardenna pacifica
- Family
- Procellariidae
- Average incubation period
- About 50 days
- Average fledging period
- 103–115 days
- Typical diet
- Fish, squid, and crustaceans
- Maximum recorded dive depth
- 66 m (217 ft)
- Breeding age
- Four years
Lore & Background
The wedge-tailed shearwater was formally described in 1789 by German naturalist Johann Friedrich Gmelin in his revised edition of Carl Linnaeus's Systema Naturae, under the binomial name Procellaria pacifica. Gmelin based his description on the 'Pacific petrel' described in 1785 by English ornithologist John Latham. The type locality was later designated as the Kermadec Islands by Gregory Mathews in 1912. The species is now placed in the genus Ardenna, introduced in 1853 by Ludwig Reichenbach, and is monotypic with no recognized subspecies. A 2022 molecular phylogenetic study found it to be sister to Buller's shearwater.
This species is the largest of the tropical shearwaters and occurs in two color morphs: dark and pale. Pale morphs predominate in the North Pacific, while dark morphs are more common elsewhere, though both morphs exist in all populations and are unrelated to sex or breeding condition. Its common name comes from its large, wedge-shaped tail, which may aid gliding. The bill is dark, and the legs are salmon pink, set far back on the body as an adaptation for swimming. The wedge-tailed shearwater is related to Buller's shearwater, which also has a wedge tail and thin black bill, and together they form the Thyellodroma group.
Reader's Guide
The wedge-tailed shearwater is a significant species within tropical seabird ecosystems, serving as an indicator of marine health through its pelagic feeding on fish, squid, and crustaceans. Its diet is 66% fish, with goatfish being the most commonly taken prey. While earlier observations suggested surface feeding, a 2001 study using maximum depth recorders found that 83% of wedge-tails dived during foraging trips, reaching a mean maximum depth of 14 m and a maximum of 66 m. This species breeds colonially on small tropical islands, with synchronized breeding seasons more common at higher latitudes. Northern Hemisphere birds begin breeding around February, Southern Hemisphere birds around September. They display natal philopatry, returning to their natal colony at age four. Wedge-tailed shearwaters are monogamous, forming pair bonds that last several years, with divorce occurring after failed breeding seasons. Their nesting occurs in burrows or under surface cover, and they are known to evict Bonin petrel chicks from burrows when returning to breed. The species' Hawaiian name 'Uau Kani' reflects its moaning call, which consists of an inhaling 'OOO' and exhaling 'err' component. Its conservation status is not specified in the source, but its wide distribution across the tropical Pacific and Indian Oceans suggests a relatively stable population, though local threats may exist.
Did You Know?
- The wedge-tailed shearwater is the largest of the tropical shearwaters.
- Its Hawaiian name 'Uau Kani' means 'moaning petrel,' reflecting its call.
- A 2001 study found that 83% of wedge-tailed shearwaters dived during foraging trips, reaching depths up to 66 m.
- The species is monotypic, with no recognized subspecies.
Frequently Asked Questions
Who is Wedge-tailed shearwater?
The Wedge-tailed shearwater (Ardenna pacifica) is a medium-large pelagic seabird in the Procellariidae family, instantly recognizable by its pointed, wedge-shaped tail. In Hawaiian tradition it goes by the names Uau Kani and Koto, and it is one of the species people loosely call a muttonbird.
What are Wedge-tailed shearwater's abilities and role in the ocean?
This shearwater is a capable deep-diver, with a maximum recorded depth of 66 meters, where it hunts fish, squid, and crustaceans. It functions as a mid-level predator linking pelagic prey to higher trophic levels across the tropical Pacific and Indian Oceans.
What is Wedge-tailed shearwater's breeding lifecycle?
After roughly 50 days of incubation, the single chick needs another 103 to 115 days to fledge and join the adults at sea. The species returns to island colonies off Japan, Hawaii, the Seychelles, the Marianas, and Australia to reproduce each season.
Why is Wedge-tailed shearwater important to its ecosystem?
By preying on small pelagic fish and squid over a range spanning roughly 35°N to 35°S, it helps keep those prey populations in check and transfers oceanic energy to island-based food webs. Its presence at breeding sites also serves as a useful indicator of the health of those island and nearshore marine habitats.
What are the two color morphs of Wedge-tailed shearwater?
The species exhibits two distinct plumage variants, which can make quick field identification a challenge for observers. Both morphs share the same wedge-tailed silhouette, the same tropical oceanic range, and the same foraging behavior.
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