Hawaiian Name: ʻUaʻu kani
The Wedge-tailed Shearwater is a very wide-ranging seabird, and one of the most common seabirds in Hawaiʻi. Breeding populations of this species occur on ocean islands throughout the tropical Indian and Pacific Oceans from Madagascar to Mexico. Wedge-tailed Shearwater colonies occur on almost every island in the Hawaiian Chain, where they nest at low-elevation sites in burrows under sand, soil, tree roots or in loose rocks. The largest populations are in the Northwestern Hawaiian Islands (230,000 pairs), but significant colonies are found in the Southeastern Hawaiian Islands (67,000 pairs) as well, with some of the largest colonies on Lehua Islet, Kauaʻi, and islets off of Oʻahu, Maui, and Molokaʻi. Wedge-tailed Shearwaters also breed sporadically on Lanaʻi, Kahoʻolawe, and Hawaiʻi.
Wedge-tailed Shearwaters are very easily seen from shore with binoculars during the breeding season from March through November, and particularly in the evening as they are returning to the colonies, but they can be seen at almost any time of day. Wedge-tailed Shearwaters are also very commonly seen from boats even just a few miles from shore where they are often seen in dense flocks either resting on the water or feeding over schools of fish. Wedge-tailed Shearwaters in Hawaiʻi feed largely on small fish driven to the surface by schools of Tuna or other large predatory fish, thus giving them the name “Tuna Birds”. This habit of following feeding schools of tuna also helps fishermen locate school of fish by simply looking for flocks of Wedge-tails. These flocks of Wedge-tailed Shearwaters also attract other species of seabirds, such as Newell’s Shearwaters, Hawaiian Petrels, Bulwer’s Petrels, Red-footed and Brown Boobies, and Noddies, and are quite an impressive sight to see.
When Wedge-tailed Shearwaters come to shore at night they are very uncoordinated and typically land by stalling and crashing in to the ground or low vegetaion. They then find their burrow and start calling in a very distinctive, and somewhat ethereal moaning sound that gives them their Hawaiian name, ʻUaʻu kani. The birds will often sit in their burrow or just outside the burrow for most of the day and are often quite easy to see at protected locations such as Kilauea Point NWR on Kauaʻi or Kaena Point on Oʻahu during the breeding season.
The Wedge-tailed Shearwater occurs in either a light morph or a dark morph in all populations, but in Hawaii the light morph predominates. Light morph individuals have a mostly white or whitish underside and brown upperside, while dark morph individuals are completely dark brown above and below. This range of variation in appearance can often cause confusion with other species of shearwaters and petrels in Hawaii, including Newell’s Shearwater, Hawaiian Petrel, and Christmas Shearwater. However, Wedge-tailed Shearwater outnumbers all of those species in Hawaiian waters, so ‘chances are’ that you’re looking at a Wedge-tailed instead of another species. Please see the species accounts for the other shearwaters and petrels for tips on how to separate them from Wedge-tailed Shearwater. Photos of both dark and light morph Wedge-tailed Shearwaters are below. The species is named for its distinctive wedge shaped tail, which is usually held closed and gives it a long-tailed look.
Despite being a very common seabird in Hawaiʻi, they are still subject to many human-caused threats, including predation by cats, dogs, rats, mongoose, and owls at the breeding colonies, inadvertent trampling of nesting burrows by cattle and people, ingestion of plastics in the ocean, habitat destruction in coastal areas due to construction and invasive plants, collision with powerlines, buildings, and vehicles at night, and depletion of fishing stocks. Despite this myriad of threats, the species populations appear to be stable and is listed by the IUCN as “Least Concern”. Historically, the populations in Hawaii have experienced huge fluctuations in size due to human caused threats such as direct hunting for food, predation by rats, and disturbance during WWII, so populations should continue to be monitored.