The Sooty Shearwater (Puffinus griseus) is a medium-sized shearwater bird that undertakes one of the longest yearly migrations of any animal on Earth. Each year, Sooty Shearwaters travel from their breeding grounds in New Zealand, Chile, and the Falkland Islands to the North Pacific Ocean off the coast of Japan, Alaska, and California. This immense journey spans over 40,000 miles and allows the Sooty Shearwater to take advantage of the austral summer in the Southern Hemisphere and the boreal summer in the Northern Hemisphere. The Sooty Shearwater’s migration pattern has fascinated researchers for decades and demonstrates the incredible navigational abilities of seabirds.
Breeding Distribution
Sooty Shearwaters nest on offshore islands around New Zealand, southeastern Australia, Lord Howe Island, the Juan Fernandez Islands off Chile, and the Falkland Islands in the South Atlantic. The largest colonies containing over 90% of the global population are located in New Zealand. Sooty Shearwaters nest in burrows dug into soil or sand underneath vegetation. Breeding takes place from September to March during the austral summer.
Key breeding locations include:
- New Zealand – Tītī Islands, Snares Islands, Solander Islands
- Southeastern Australia – Hunter Island, Pedra Branca
- Chile – Isla Mocha, Isla Robinson Crusoe
- Falkland Islands – many offshore islands
Migration Pattern
After breeding concludes in March and April, Sooty Shearwaters embark on a clockwise loop migration up the western coasts of South and North America. The timing and exact routes may vary between different populations:
- Birds originating from New Zealand first head east towards South America. In April and May, they pass south and east of Australia towards Chile and Peru. Some birds stop to feed off the Humboldt Current.
- In May and June, Sooty Shearwaters migrate northwards hugging the coastline up to Alaska. They forage extensively along productive upwelling regions off California and British Columbia.
- Through July and August, the birds move west across the northern Pacific Ocean to waters off Russia, Japan, and China following prey resources.
- The southbound return journey occurs from August to October down the western Pacific to New Zealand.
Sooty Shearwaters traveling this figure-8 route may cover over 40,000 miles during their annual odyssey. However, those originating from Chile and the Falklands likely take a shorter route hugging the west coastlines of South and North America.
Navigation
Sooty Shearwaters employ a combination of innate instincts and learned behaviors to navigate their marathon migrations. Several adaptations help them stay on course over thousands of miles of open ocean:
- Sensory abilities – shearwaters use their keen eyesight during daytime in combination with their exceptional sense of smell to detect faint odor cues from prey, oceanic fronts, and the dimethyl sulfide produced by phytoplankton.
- Sun compass – on sunny days, shearwaters orient themselves relative to the sun’s position.
- Stars – on clear nights, the birds navigate using stars and constellations.
- Geomagnetism – shearwaters detect minute variations in the Earth’s magnetic field to maintain direction.
- Visual landmarks – memory of known coastlines, islands, and oceanographic features helps guide their travels.
- Genetic instincts – young shearwaters imprint on their future migratory routes and key stopover sites from experienced adults.
The Sooty Shearwater thus integrates multiple wayfinding strategies spanning the sun, stars, waves, wind, smell, memory, and genetics to track their migratory route year after year with amazing precision.
Timing
The timing of the Sooty Shearwater’s migration is closely tied to seasonal availability of their prey and breeding cycle. Key events include:
Months | Activity |
---|---|
September – March | Breeding season in the Southern Hemisphere |
April – May | Northward migration up western South America |
May – June | Travel north along North American coastline |
July – August | Cross North Pacific to Asia following prey |
August – October | Return migration down western Pacific |
Sooty Shearwaters thus schedule their travels to take advantage of peak seasonal abundance of small fish, krill, and squid at highly productive feeding areas along their migratory route.
Threats and Conservation
Several threats confront Sooty Shearwater populations during migration, negatively impacting their numbers:
- Fisheries bycatch – becoming accidentally caught in fishing nets
- Ingestion of plastics – mistaking plastic for prey
- Predation by introduced mammals – especially on breeding islands
- Climate change – disruption of marine food webs and ocean currents
- Habitat degradation at breeding sites
Conservation efforts are focused on mitigating these threats through measures such as:
- Working with fisheries to reduce seabird bycatch
- Removing invasive predators from breeding islands
- Reducing ocean plastic pollution
- Establishing marine protected areas along the migration route
- Ongoing monitoring of populations and breeding success
Further research tracking individual Sooty Shearwaters with tiny GPS tags will provide new insights into their migratory timing, routes, stopover sites, and at-sea habits. This information can help target conservation efforts along their vast migratory range.
Conclusion
The epic yearly migration of the Sooty Shearwater is one of the most astonishing feats of navigation in the animal kingdom. By traveling up to 40,000 miles between nesting burrows in the Southern Hemisphere and feeding grounds in the Northern Pacific, Sooty Shearwaters demonstrate incredible homing instincts and reliance on environmental cues for orientation. However, human impacts on the marine environment increasingly threaten the survival of these marathon migrants. Ongoing conservation initiatives aimed at protecting Sooty Shearwaters throughout their migratory range are crucial for ensuring the persistence of their amazing ocean-spanning journeys.