Shearwaters are a group of seabirds in the family Procellariidae. There are around 30 species of shearwaters found across the world’s oceans. Some of the most well-known species include the Manx shearwater, sooty shearwater, short-tailed shearwater, and flesh-footed shearwater.
What do shearwaters look like?
Shearwaters are medium to large seabirds with long, narrow wings. Their bodies are streamlined which allows them to glide low over the ocean when hunting for food. Most species have dark plumage on their back and upperwings that contrasts with their white undersides. This countershading camouflages them from predators when viewed from above or below.
They have long, hooked bills that are adapted for catching fish, squid, and other marine prey while swimming. Unlike many seabirds, shearwaters do not have webbed feet. Their feet have three forward-facing toes to provide propulsion while swimming and diving.
In flight, shearwaters have stiff wing beats and make twisting or shearing motions with their wings to gain lift. This unique flight style gives the group their common name of “shearwater”.
Where do shearwaters live?
Shearwaters have a worldwide distribution across the oceans in both the Northern and Southern Hemispheres. Different species occupy various oceanic regions and habitats:
- Manx shearwaters – North Atlantic and Mediterranean
- Sooty shearwaters – Pacific, Atlantic, and Indian Oceans
- Short-tailed shearwaters – Pacific and Indian Oceans
- Flesh-footed shearwaters – Pacific and Indian Oceans
While most shearwater species live exclusively out at sea, some migrate to coastal areas or islands during the breeding season. Shearwaters nest in underground burrows or crevices and only come to land to breed. Their chicks hatch in these burrows and remain there until they fledge and head out to sea.
What do shearwaters eat?
Shearwaters feed on a variety of marine life while swimming and diving underwater. Some of their key prey items include:
- Small fish like anchovies, sardines, and lanternfish
- Squid
- Crustaceans like krill and shrimp
- Jellyfish
Shearwaters use their excellent sense of smell to locate patches of prey while flying over the ocean. They can dive to depths over 65 feet to pursue schools of fish and squid. Many species will also feed on scraps and bait near fishing boats.
How do shearwaters reproduce?
Shearwaters are colonial nesters, meaning they nest in large aggregations with hundreds or thousands of other pairs. Their breeding seasons and behaviors vary by region:
- Northern Hemisphere species breed April – November
- Southern Hemisphere species breed October – May
Courtship activities like billing (touching bills) and vocalizing help pairs reinforce their bonds. Both the male and female participate in choosing a nest site, building the nest, incubating the egg, and caring for the chick.
The parents take turns incubating the single white egg for around 50 days. Once hatched, the chick is brooded and fed by the parents until it fledges at 8-12 weeks old. Parents identify their chick by its unique call.
How do shearwaters navigate?
Shearwaters embark on incredibly long migrations each year, with some species flying over 40,000 miles roundtrip. They rely on several advanced sensory adaptations to navigate across the open ocean:
- Olfaction – shearwaters have an acute sense of smell and can detect trace amounts of dimethyl sulfide gas which helps them locate prey.
- Polarized light – specialized receptors in their eyes allow them to determine direction based on sunlight polarization patterns.
- Magnetic senses – shearwaters are thought to navigate using the Earth’s magnetic fields.
- Stars and sun – they use celestial cues from stars and the sun’s position to maintain their bearing.
By integrating these orientation systems, shearwaters can migrate across entire ocean basins to return to their breeding colonies each year.
Threats facing shearwaters
Many shearwater populations today face a variety of threats on both their breeding and non-breeding grounds:
- Predation from invasive species like rats, cats, and foxes
- Habitat degradation
- Light pollution that causes disorientation
- Ingestion of plastics and marine pollution
- Longline fishing bycatch
- Climate change and severe weather
- Disturbance of nesting colonies
Several shearwater species have declining populations, including the Balearic shearwater, Christmas Island shearwater, and Townsend’s shearwater which are critically endangered.
Interesting facts about shearwaters
- Shearwaters are champion marathon migrants – the sooty shearwater makes the longest migration of any animal, flying about 40,000 miles roundtrip each year between New Zealand and the North Pacific.
- They use a technique called “dynamic soaring” to travel long distances without flapping, exploiting differences in wind speed and direction.
- Shearwater chicks hatch with only one wing 70% developed. They use this wing to propel themselves to the burrow entrance before both wings fill out.
- Ancient Polynesians used the flight patterns of shearwaters to help them navigate and colonize the Pacific islands.
- Shearwater parents and chicks can recognize each other’s unique calls even among thousands of other nesting birds.
- The oldest known wild shearwater was a Manx shearwater that lived to over 50 years old.
Key shearwater species
Here are some of the most widespread and recognizable shearwater species around the world:
Species | Range | Description |
---|---|---|
Manx shearwater | North Atlantic and Mediterranean | Black upperparts and white underparts. Stocky body. Breeds on islands and coastal cliffs. |
Sooty shearwater | Pacific, Atlantic, and Indian Oceans | All dark plumage. Slender shape. Makes longest known bird migration. |
Short-tailed shearwater | Pacific and Indian Oceans | Dark gray and white. Medium-sized with short tail. Forages in large flocks. |
Great shearwater | Atlantic and eastern Pacific | Dark brown and white. Large shearwater often associated with storms at sea. |
Pink-footed shearwater | Pacific Ocean off South America | Gray and white with pink bill and legs. Makes trans-equatorial migrations. |
Flesh-footed shearwater | Pacific and Indian Oceans | Pale underparts and brown head. Unusual flesh-colored feet. |
Conclusion
Shearwaters are remarkable pelagic seabirds capable of migrating thousands of miles across the world’s oceans. While they spend most of their lives at sea, shearwaters rely on islands and coastal areas for breeding colonies. They use a suite of sensory adaptations for navigating and locating patchy prey. Many shearwater populations today are threatened by human activities and face conservation challenges. These unique seabirds illustrate the resilience and beauty of marine life.