Black-vented Shearwater, Puffinus opisthomelas

Black-vented Shearwater, Puffinus opisthomelas. Photographs taken at sea in coastal waters of Baja California Sur. Fairly frequent visitors to a drifting fishing Panga looking for handouts.

Background and Identification

The Black-vented Shearwater, Puffinus opisthomelas, is a member of the Procellariidae Family of Shearwaters and Petrels. They are medium-sized seabirds known for their distinctive colorings and agile flight patterns. Spending most of their time at sea, they are mostly spotted by fishermen and other boaters and cruisers. Their diet consists solely of fish, specifically Northern Anchovies, Pacific Sardines, and limited amounts of squid. When feeding, the shearwater plunges from the surface of the sea and dives to depths over 20 m (130 feet) into the water. Very little is known about this species, as it breeds on a remote island off the coast of Baja California Sur in Mexico and has nocturnal breeding and nesting habitats. In Mexico, this species is called Pardela Mexicana.

As mentioned, Black-vented Shearwaters are mid-sized in stature, ranging from 12 cm (4.7 inches) to 15 cm (5.9 inches) and weighing approximately 400 g (14.1 oz). This species is sexually monomorphic, meaning that males and females do not have highly distinguishable differences in appearance. The plumage of both sexes is identical. Adults have a dark brown to black upper body, including the head, wings, and back, with a contrasting white underbody. The bird gets its name from the black coloration around its vent area. They have long, slender wings adapted for dynamic soaring and gliding over the ocean.

Habitat and Geographical Range

Black-vented Shearwaters primarily inhabit the Pacific Ocean, specifically the coastal waters off the western coast of North America. During the non-breeding season, Black-vented Shearwaters disperse widely over the ocean but generally remain within the Pacific coastal regions. They are often seen near upwelling zones and other areas with high marine productivity, where they hunt.

They are most commonly found from California to Baja California in Mexico, where they spend a significant portion of their time at sea. These birds breed on islands off the coast of Baja California, such as Isla Natividad, Isla Guadalupe, and Isla San Benito. In Mexico, they are found within the coastal regions of the Pacific Slope north of Guerrero within 25 km (15 miles) of the coast at elevations up to 100 m (330 feet).

Common Misidentifications

The Black-vented Shearwater can be confused with other shearwater species that share similar habitats, such as the Sooty Shearwater, Ardenna grisea, and the Pink-footed Shearwater, Ardenna creatopus. The Sooty Shearwater is darker overall, with uniformly sooty-brown plumage, and lacks the stark contrast between the upper and lower body seen in the Black-vented Shearwater. The Pink-footed Shearwater has a more mottled appearance with pinkish legs and feet, which distinguishes it from the Black-vented Shearwater.

Conservation Status

From a conservation perspective, the Black-vented Shearwater is currently considered to be Near Threatened. Their populations were decimated by the release of domestic cats that became feral on their breeding islands. Efforts to remove these cats and other domestic animals from the island have recently increased in success, and the populations of the Black-vented Shearwater are starting to recover. More than 95% of the breeding populations occur on Navidad Island in Baja California Sur, Mexico.