Shearwaters are medium-sized long-winged seabirds in the family Procellariidae. There are around 30 species of shearwaters that are found worldwide, mostly in the Southern Hemisphere. Some key characteristics of shearwaters include:
What do shearwaters look like?
Shearwaters have long, narrow wings that allow them to fly long distances while expending little energy. Their bodies are streamlined and their legs are set far back on their bodies to aid in swimming. Shearwaters have webbed feet and sharp hooked bills that help them catch fish and squid.
Most species are grey, black, brown or white in color on their backs, with white undersides. Some species like the Great Shearwater have dark caps or hoods. Shearwaters range in size from 25-65 cm in length and weigh 200g to over 800g depending on the species.
Where do shearwaters live?
Shearwaters are pelagic birds, meaning they spend most of their lives out at sea. They only come to land to breed. Different species have breeding ranges across the Southern Hemisphere:
- The Great Shearwater breeds on islands off South America.
- Sooty Shearwaters and Short-tailed Shearwaters breed on islands around New Zealand, Australia, Chile and Argentina.
- Cory’s Shearwater breeds in the North Atlantic Ocean.
- Manx Shearwaters breed on islands off the coasts of the United Kingdom and North America.
- Pink-footed Shearwaters breed on islands off Chile and Peru.
During the non-breeding season, shearwaters migrate long distances across the oceans to feed. Some species like the Sooty Shearwater undertake the longest migration of any bird – covering over 64,000 km annually roundtrip between breeding and feeding grounds!
What do shearwaters eat?
Shearwaters feed on small fish, squid, krill and other marine creatures. They capture prey by plunging into the water from flight or by dipping while swimming along the surface. Their diet consists mainly of:
- Small fish – anchovies, sardines, mackerel
- Squid
- Crustaceans – krill, shrimp, crabs
Shearwaters have adaptations for processing high-fat diets, including an enlarged liver and the ability to store large amounts of body fat. This allows them to go for long periods without eating during migrations or incubation duties.
How do shearwaters reproduce?
Shearwaters return to breeding colonies from September to November. They nest in underground burrows or crevices on offshore islands. Shearwaters are monogamous, mating with the same partner year after year. Courtship involves billing, mutual preening and vocalizations between the male and female.
The female lays a single white egg each season. Parents take turns incubating the egg for around 50 days until it hatches. The chick is semi-altricial, meaning it hatches with eyes open and some downy feathers but still requires parental care.
Both parents feed the chick by regurgitating oil-rich food into its mouth. The chick fledges at around 70-100 days old. Shearwaters live long lives for seabirds, up to 30 years in some species.
How do shearwaters navigate?
Shearwaters migrate enormous distances across featureless oceans to return to their breeding and feeding grounds each year. They navigate using a combination of abilities:
- Sense of smell – can detect trace odors to locate prey and navigational cues.
- Magnetic senses – detect the Earth’s magnetic fields to maintain direction.
- Sun compass – use the sun’s position to determine direction.
- Star navigation – use stars and the Milky Way to orient at night.
- Memorization – remember landmarks and ocean features to navigate.
Their ability to pinpoint remote islands after migrating thousands of miles is an incredible navigational feat. Some young birds likely learn migration routes and site locations from experienced adults.
Are shearwaters endangered?
Many shearwater species face threats from human activities and are declining in numbers. The main threats include:
- Predation by invasive species at breeding colonies
- Habitat destruction
- Overfishing of food sources
- Ingestion of plastics
- Climate change affecting prey availability
- Fisheries bycatch
Some of the most threatened shearwater species include:
Species | Conservation Status |
---|---|
Balearic Shearwater | Critically Endangered |
Yelkouan Shearwater | Vulnerable |
Christmas Island Shearwater | Endangered |
Conservation efforts are ongoing to protect and restore shearwater populations. These include eradicating invasive species, reducing bycatch, and protecting breeding habitat.
What is the cultural significance of shearwaters?
Shearwaters have long held cultural significance for indigenous peoples across the Southern Hemisphere. Examples include:
- New Zealand Māori consider the Tītī or Sooty Shearwater to be a taonga (treasure). Their annual migration was used to predict weather patterns and harvest seasons.
- The Short-tailed Shearwater or Muttonbird is culturally significant for Aboriginal Australians. Sustainable harvesting of chicks and eggs provided an important seasonal food source.
- Ancient Polynesians used the flight patterns of Wedge-tailed Shearwaters to navigate and discover new islands across the Pacific.
Shearwaters remain important to coastal communities today through sustainable harvesting, ecotourism, and conservation efforts that protect the birds and their breeding habitats.
Conclusion
Shearwaters are remarkable seabirds that spend most of their lives at sea, but return to remote islands each year to breed. They are supreme navigators, using a suite of skills to migrate enormous distances across the oceans. While many shearwater populations are declining due to human impacts, conservation efforts combined with sustainable traditional practices are helping to protect these culturally significant birds into the future.