Manx shearwaters are medium-sized seabirds that breed on islands off the coasts of Europe and North America. They are known for their epic migration journeys across the Atlantic Ocean. But exactly how far do they travel on these remarkable journeys?
Migration Overview
Manx shearwaters nest in colonies on islands from May to September. After the breeding season ends, they migrate south towards South America. Their wintering areas are along the coasts of Argentina, Uruguay, Brazil and Chile. In the spring, they make the return migration back north to their breeding islands. The total round trip migration can cover over 10,000 miles (16,000 km).
Manx shearwaters are pelagic seabirds, spending most of their lives out in the open ocean. They use ocean currents and winds to aid their migration and travel enormous distances. Satellite tracking studies have provided detailed insights into their migration routes and timing.
Fall Migration Route
After leaving their breeding colonies, Manx shearwaters first migrate west towards North America. Birds from Iceland, Scotland, Ireland and Wales make a direct flight of around 2,500 miles (4,000 km) towards Canada and the northeast United States. Further south, birds from the Azores head towards the east coast of North America. Their initial migratory flights last 6-12 days nonstop over the ocean.
Along the Atlantic coast of North America, the shearwaters stop to rest and feed for 2-3 weeks. This allows them to rebuild their energy and fat reserves for the next long migration leg. Their main stopover sites are around Nova Scotia, Newfoundland and Georges Bank off New England.
In late September and October, the Manx shearwaters depart North America and migrate down to South America. This is the longest part of their migration, covering 4,500-6,500 miles (7,200-10,500 km) over the Atlantic Ocean. They follow prevailing winds and ocean currents, taking a looping course towards northeast Brazil. Birds from Canada first fly east into the Atlantic before turning south. Birds from the northeast U.S. follow a more direct southbound track towards the Caribbean and South America.
The journey from North America to South America takes around 12-20 days of continuous flying. Their flight speed averages around 310 miles per day (500 km/day). Eventually they reach the productive waters off South America in November and December, their wintering destination after the long fall migration.
Key Facts About the Fall Migration Route
- Breeding to North America: 2,500 miles (4,000 km)
- North American stopover: 2-3 weeks in September
- North America to South America: 4,500-6,500 miles (7,200-10,500 km)
- Total fall migration distance: 7,000-9,000 miles (11,000-14,500 km)
Spring Migration Route
The spring migration northwards happens between March and May. The timing depends on exactly where the shearwaters have spent the winter – those off Uruguay and southern Brazil depart first, while birds further north in the Caribbean leave later.
Initially the Manx shearwaters migrate northeast across the Atlantic on a broad front. As they reach the longitude of North America, their routes split to either side of the continent. Birds heading for Canada move north along the U.S. east coast, while those from farther south migrate towards Central America and up the Atlantic side.
In April and May, the shearwaters return to their North American stopover sites to rest and feed again for 2-3 weeks. The main spring stopovers are off the Carolinas, Virginia, Long Island and southern New England. Some birds may not stop but continue directly back to their breeding islands.
For the final migratory leg, the Manx shearwaters make a direct flight back to their individual nesting islands. Birds breeding in Iceland cover around 1,800 miles (3,000 km) over 4-7 days. Birds from the Azores, Madeira and Canary Islands fly 1,200-2,500 miles (2,000-4,000 km) over 5-10 days to return.
Upon reaching the breeding colonies in late April or May, the shearwaters reunite with their established mate. After the astonishing round trip migration of up to 10,000 miles (16,000 km), the birds are ready to breed again.
Key Facts About the Spring Migration Route
- South America to North America: 3,500-5,500 miles (5,600-8,800 km)
- North American stopover: 2-3 weeks in April/May
- North America to breeding islands: 1,200-2,500 miles (2,000-4,000 km)
- Total spring migration distance: 4,700-8,000 miles (7,600-12,900 km)
How Do Manx Shearwaters Navigate Their Migration?
The massive migrations of Manx shearwaters rely on advanced sensory capabilities and navigational skills. Their main navigation mechanisms include:
- Magnetic senses – Shearwaters contain tiny magnetic particles in their beaks and heads. These allow them to detect the Earth’s magnetic field like a natural compass and determine their latitude and longitude.
- Sun compass – On sunny days shearwaters use the position of the sun to orient themselves and maintain their heading.
- Star compass – On clear nights they navigate using the positions of stars.
- Polarized light – They can detect polarized light patterns in the sky near sunrise and sunset, providing navigational cues.
- Smell – Shearwaters have an acute sense of smell which may allow them to locate their breeding and feeding areas.
In addition, Manx shearwaters likely have a complex mental map and spatial memory that allows them to navigate over such vast distances. Their navigational skills are finely tuned and passed on from generation to generation through learning.
Threats Faced During Migration
Manx shearwaters face a number of threats during their migratory journeys across the Atlantic Ocean. These include:
- Predation – Large gulls may kill adults at breeding colonies. Skuas and jaegers attack them at sea.
- Severe weather – Storms and hurricanes can blow shearwaters off course or cause exhaustion.
- Starvation – Finding enough food across entire journeys is challenging.
- Fisheries – Accidental bycatch in longline fishing gear.
- Pollution – Plastics and ocean pollution can be ingested or cause entanglement.
- Habitat loss – Declines in prey due to overfishing and climate change.
Migrating shearwaters also face threats at their breeding and wintering sites from introduced predators. Conservation efforts are aimed at protecting key stopover habitats and reducing fisheries bycatch.
Research Techniques to Study Manx Shearwater Migration
Ornithologists have used various research techniques to study the remarkable migrations of Manx shearwaters:
- Leg rings – Metal bands placed on birds’ legs provide recovery information on migration routes and lifespan.
- Geolocators – Small tracking devices record light levels to estimate location.
- GPS loggers – Devices attached to the birds record accurate locations during migration.
- Satellite tracking – Transmitters beam location data back via satellite allowing real-time tracking.
- Stable isotope analysis – Chemical analysis of feathers provides clues about diet and latitudes traveled.
In particular, satellite tracking since the 1990s has revolutionized understanding of shearwaters’ migratory timing, routes, stopping areas and oceanic habits. Tracking studies continue to reveal new details about their epic migrations each year.
Comparison to Other Shearwater Species
Several other shearwater species make long migrations in the Pacific and Atlantic Oceans. Some examples and how they compare to Manx shearwater migrations:
Species | Breeding Area | Winter Area | Migration Distance |
---|---|---|---|
Manx shearwater | North Atlantic | South Atlantic | 7,000-10,000 miles |
Sooty shearwater | New Zealand, Chile | North Pacific | 12,500 miles |
Great shearwater | South Atlantic | North Atlantic | 5,000 miles |
Wedge-tailed shearwater | Hawaiian Islands | North Pacific | 4,500 miles |
Short-tailed shearwater | Australia | North Pacific | 9,000 miles |
The sooty shearwater makes the longest migration, flying an incredible 12,500 miles (20,000 km) each year around the Pacific Ocean. However, the Manx shearwater’s combination of breeding in the North Atlantic and wintering in the South Atlantic makes it the champion for cross-ocean migrations.
Future Research Directions
There are still aspects of Manx shearwater migration that can be better understood through future studies:
- Juvenile migration patterns are unknown – tracking juveniles on their first migrations would provide new insights.
- Individual consistency in routes and timing – do shearwaters follow the same routes each year?
- Foraging behavior – detailed monitoring of their feeding habits while migrating.
- Impact of climate change – how a changing ocean may alter migratory movements.
- Mortality rates – better data on survival threats during different migration stages.
New tracking technology and analytical techniques will help address these knowledge gaps. Biologging devices are becoming smaller and more advanced, allowing collection of detailed behavioral data over entire migration cycles.
Conclusion
Manx shearwaters are champions of migration, traveling enormous distances between their North Atlantic breeding islands and wintering areas off South America. Their annual round trips can cover 7,000-10,000 miles (11,000-16,000 km), crossing the Atlantic Ocean multiple times.
Extensive research using tagging, tracking devices and chemical analysis has uncovered the details of their migratory routes, timing, navigation and threats. However, mysteries remain around their foraging habits, consistency and adaptation to climate change. As tracking technology improves, scientists continue to gain new insights into the remarkable marathon migrations of Manx shearwaters.