Cory's Shearwater

Calonectris diomedea

Order: Procellariiformes / Family: Procellariidae

gray brown white large seabird coastal migratory colonial nocturnal common

About the Cory's Shearwater

Cory's Shearwater (Calonectris diomedea) plays a significant role in marine ecosystems as a pelagic seabird, primarily inhabiting the open ocean. It is part of the Procellariidae family, known for its long-distance migrations and impressive flying abilities. These birds are endemic to the Mediterranean and surrounding Atlantic regions, exhibiting a preference for cliffside nesting sites on islands such as the Azores, Madeira, and the Canary Islands. Due to their affinity for the ocean, Cory's Shearwaters spend most of their lives at sea, coming ashore only to breed. Their presence is a crucial indicator of ocean health, as they are top predators in the marine food web, preying on squid, fish, and other marine organisms. Cory's Shearwaters are known for their long migratory routes, traveling from their breeding grounds in the North Atlantic to wintering locations along the South American and African coasts. This extensive migration underscores their adaptability and resilience in the face of environmental changes. During the breeding season, these birds are highly vocal, with eerie calls that resonate across their nesting colonies, adding to the distinctive soundscape of remote island cliffs. Their ecological role extends beyond predation, as they also influence nutrient cycles through their guano deposits, which enrich island soils and support plant life. As climate change and human activities alter marine environments, Cory's Shearwaters face challenges such as habitat disturbance, pollution, and changes in prey availability. Consequently, they serve as important bioindicators for monitoring the health of marine ecosystems. Their continued survival highlights the interconnectedness of marine and terrestrial environments, emphasizing the need for comprehensive conservation efforts to protect these remarkable avian travelers.

The Cory's Shearwater belongs to the family Procellariidae, within the order Procellariiformes. These birds typically live average lifespan is about 20-25 years, with a maximum recorded of over 30 years..

How to Identify a Cory's Shearwater

Cory's Shearwater is a large seabird with a wingspan of up to 126 cm, making it an impressive sight in flight. Adults feature a predominantly gray-brown upper body with a stark white underside, which is particularly visible during its distinctive gliding flight over the ocean. The bird's head is a softer gray, often appearing slightly lighter than the back, with a pale yellowish bill that curves gently downward. This robust bill is a key identifying feature. Juveniles resemble the adults but may have slightly duller plumage. Both males and females appear similar, making gender differentiation difficult in the field. Cory's Shearwater can be confused with the Great Shearwater, but the latter typically has a more prominent white patch on the rump. In flight, Cory's Shearwater exhibits a unique silhouette with its long, narrow wings held stiffly, allowing it to soar effortlessly with minimal wing beats. When resting on the water or land, it maintains a low, horizontal posture, often appearing quite relaxed. Observers can identify it by its distinctive flight pattern, characterized by long, gliding arcs and minimal flapping, which is ideal for covering vast ocean distances.

Having trouble telling birds apart? Upload a photo to our bird identification tool for an instant species match.

Cory's Shearwater Habitat and Range

Preferred Habitat

Cory's Shearwater primarily inhabits pelagic zones, thriving in the open ocean where it spends the majority of its life. Breeding colonies are typically located on remote islands with steep cliffs, which offer protection and easy access to the sea. The Azores, Canary Islands, and Madeira provide ideal breeding habitats, featuring rugged landscapes with minimal human disturbance. Outside of the breeding season, Cory's Shearwaters remain oceanic, rarely venturing close to continental coastlines except during migration. These birds are adapted to life far from land, often found in waters ranging from temperate to tropical zones, depending on the season. They exhibit minimal habitat shifts as they migrate, consistently favoring areas with abundant marine life. Elevation is not a significant factor in their habitat preferences, as they are mostly found at sea level. In contrast to urban areas, Cory's Shearwaters are strictly oceanic, rarely seen inland except when blown off course during storms.

Geographic Range

Cory's Shearwater breeds in the North Atlantic, with significant populations on the Azores, Madeira, and the Canary Islands. During the non-breeding season, they migrate southward to the waters off the coast of Brazil, Uruguay, and Argentina in South America, as well as the west coast of Africa. This extensive range covers both sides of the Atlantic Ocean, demonstrating their remarkable migratory capabilities. During migration, they utilize the mid-Atlantic corridor, often seen off the coast of Western Europe, including the Bay of Biscay and as far north as the British Isles. Population density is highest around their breeding islands, where they can be seen in large flocks. In winter, they disperse over a wide area, with some birds venturing into the Indian Ocean. This distribution reflects their adaptability to various marine environments, allowing them to exploit different oceanic conditions and prey availability.

Want to know which birds visit your area? Browse our backyard birds by location guides for region-specific species lists.

What Does the Cory's Shearwater Eat?

Cory's Shearwater primarily feeds on fish and squid, which they catch by surface seizing and plunge diving. Their diet includes small fish species such as sardines and anchovies, as well as cephalopods like squid. Seasonally, their diet may vary slightly, depending on the abundance and availability of prey in different ocean regions. During the breeding season, when they are more localized around their nesting islands, they may also consume crustaceans. Cory's Shearwaters are known for their impressive foraging techniques, often following fishing boats to capitalize on discarded bycatch. This opportunistic feeding behavior helps them to sustain their energy levels during long migrations. They typically feed at dawn and dusk, taking advantage of the diurnal movement of prey species. The size of their prey usually ranges from small fish and squid up to 20 cm in length, allowing them to meet their dietary needs efficiently.

Cory's Shearwater Behavior and Social Structure

Cory's Shearwater exhibits fascinating social and breeding behaviors. They are colonial nesters, forming large, dense colonies on remote islands. During the breeding season, these birds engage in elaborate courtship displays, which include synchronized flight patterns and vocalizations. Their eerie calls can be heard echoing across their nesting sites as they establish territories and bond with mates. Cory's Shearwaters are generally monogamous, with pairs returning to the same nesting sites year after year. They are not highly aggressive but will defend their nesting areas from intruders. Outside the breeding season, they are more solitary, dispersing widely across the ocean. These birds are primarily active during the night when they forage and engage in social interactions at sea. Their nocturnal habits help them avoid many predators, although they remain vulnerable to skua attacks at their nesting colonies. Cory's Shearwaters demonstrate remarkable navigational skills, using environmental cues and perhaps geomagnetic fields to traverse vast ocean distances.

Cory's Shearwater Nesting and Reproduction

Cory's Shearwaters nest in burrows or crevices on rocky island cliffs, which provide protection from predators and harsh weather conditions. They often reuse the same nest sites annually, showing strong site fidelity. Nest materials include small stones, shells, and vegetation, which they arrange to form a comfortable lining. The typical clutch size is one egg, which both parents incubate for about 52 to 56 days. After hatching, the chick remains in the nest for approximately 90 to 100 days, during which both parents share feeding duties. They regurgitate pre-digested food, providing the chick with a rich diet that supports rapid growth. Cory's Shearwaters typically have one brood per year, with both parents investing heavily in the care and protection of their single offspring. The fledging period coincides with the end of the breeding season, after which the juvenile joins the adults on their migratory journey.

Cory's Shearwater Sounds and Vocalizations

Cory's Shearwater produces a range of vocalizations, most notably their haunting, guttural calls heard at breeding colonies. These calls, which resemble eerie moans or wails, play a crucial role in communication between mates and in establishing territory. Their vocalizations are most frequent during the night, contributing to the mysterious ambiance of their remote island habitats. The birds also emit shorter, more abrupt call notes during flight, which serve as contact calls with other shearwaters. Alarm calls are less common but occur when they perceive threats to their nests. While these sounds may seem unsettling to human ears, they are essential for the social structure and breeding success of Cory's Shearwaters.

Interesting Facts About the Cory's Shearwater

1Cory's Shearwater can cover up to 1,000 km in a single day during migration, showcasing remarkable endurance.
2This species can live for over 30 years, making it one of the longest-lived seabirds.
3Cory's Shearwaters have an exceptional sense of smell, which they use to locate prey and navigate the ocean.
4They were named after the American ornithologist Charles B. Cory, who contributed significantly to bird studies.
5The eerie calls of Cory's Shearwater were historically mistaken for the cries of shipwrecked sailors by mariners.
6Cory's Shearwater can dive to depths of up to 15 meters when pursuing prey, demonstrating excellent diving skills.
7Despite their graceful flight, these seabirds are awkward on land, moving with a waddling gait.

Cory's Shearwater Conservation Status

Cory's Shearwater is currently listed as Least Concern by the IUCN, but its population faces threats from habitat degradation, pollution, and climate change. Predation by introduced species, such as rats and cats, poses significant risks to nesting colonies. Conservation efforts focus on habitat protection, eradication of invasive predators, and monitoring population trends. Historically, Cory's Shearwater populations have fluctuated due to human exploitation and environmental changes, but recent conservation measures have helped stabilize some populations. Continued efforts are essential to mitigate the impacts of global warming and marine pollution, ensuring the long-term survival of this iconic seabird.