The thick-billed murre (Uria lomvia) is a large auk that is well adapted for diving to great depths in search of prey. Murres are capable of diving to impressive depths of over 200 meters (656 feet) to hunt fish and other marine organisms. In this article, we will explore how deep the thick-billed murre is capable of diving and the adaptations that allow it to plunge so deep.
Quick Facts on Thick-Billed Murres
- Species: Thick-billed murre (Uria lomvia)
- Size: 28-33 cm long (11-13 inches); weighs around 1 kg (2.2 lbs)
- Range: Arctic regions of North America, Greenland, Iceland, northern Europe, Russia
- Habitat: Coastal cliffs and rocky islands
- Diet: Fish, crustaceans, mollusks, marine worms
The thick-billed murre is a large black and white auk found in northern polar regions. It breeds in huge colonies on coastal cliffs and rocky islands. Murres feed on fish, crustaceans, mollusks, and other marine organisms. They propel themselves underwater using their wings to pursue prey at depths of over 200 meters.
Diving Adaptations
Thick-billed murres have a number of anatomical and physiological adaptations that enable them to dive to great depths:
Streamlined Body Shape
Murres have a torpedo-shaped body that reduces drag and allows them to swim swiftly through the water column in pursuit of prey. Their short tail and wings positioned far back on the body maximize propulsion.
Dense Bones
A murre’s bones are solid rather than air-filled, reducing buoyancy and making it easier for the bird to submerge. Solid bones also help counteract pressure during deep dives.
High Myoglobin Levels
Murres have muscles with high levels of myoglobin, an oxygen-binding protein. This allows the muscles to function efficiently even when oxygen levels are low at depth.
Slow Heart Rate
When diving, a murre’s heart rate slows dramatically, enabling the bird to conserve oxygen. Heart rate may decrease from 180 beats per minute at the surface to just 20 beats per minute during a dive.
Oxygen Reserves
Murres have greater blood volume than similar-sized birds at the surface. They also have large reserves of oxygen stored in their muscles. This oxygen powers deep dives.
Collapsible Lungs
A murre’s stiff-walled bronchi and flexible lungs collapse at depth, reducing buoyancy and air spaces that could cause problems with pressure.
Diving Behavior
Murres employ a pursuit diving strategy, swimming quickly through the water column to capture prey. Dives typically follow a V-shaped profile, with a rapid descent, pursuit at depth, and fast return to the surface. Here are some key aspects of murre diving behavior:
- Dive speeds of 2.4-7.5 m/sec (5-17 mph) have been recorded.
- Descent angles average around 45 degrees but can exceed 60 degrees.
- Murres may dive to depths exceeding 200 meters (656 feet) but more commonly dive to 80-120 meters (260-390 feet).
- Dives usually last 2-4 minutes but murres are capable of staying under for over 5 minutes.
- Murres have an exceptional diving capacity of over 600 dives per day.
Murres locate prey using excellent underwater vision. They propel themselves using their wings and steer with their feet. Prey is usually swallowed whole at depth. Murres may make shallow dives between deep dives to rest and recover.
World’s Deepest Diving Bird
Research using time-depth recorders attached to free-ranging thick-billed murres suggests they are likely the world’s deepest diving bird. Here are some record-breaking dives documented:
- The maximum recorded depth for a murre is 210 meters (689 feet) in the North Atlantic.
- Average maximum depth is 141 meters (463 feet).
- Murres regularly exceed 180 meters (590 feet) off the coast of Newfoundland.
- No other wild bird exceeds depths of 100 meters; many species are limited to less than 30 meters.
The depth records above suggest murres are exceptional divers even among seabirds adapted to underwater swimming. No other avian species exceeds their routine diving depths.
Dangers of Deep Diving
Extremely deep dives place thick-billed murres at risk of decompression sickness, also known as “the bends.” Nitrogen gas absorbed into the blood under high pressure can come out of solution too quickly during ascent, forming dangerous bubbles. Signs of decompression sickness have been found in murres, including bubbles in organs and disoriented behavior after surfacing from deep dives.
Barotrauma is another risk, caused by a rapid change in pressure around air spaces. Murres have been found with ruptured air sacs after deep dives. Lung collapse protects against barotrauma but very fast ascents may still cause issues. Depths beyond 200 meters increase risks for murres.
Impacts of Hunting and Climate Change
Thick-billed murre populations are declining in parts of their range. Historically, they were hunted for food, eggs, and feathers. Overharvest contributed to the demise of breeding colonies in the Gulf of St. Lawrence. Murres remain a traditional food source for some northern indigenous communities.
Climate change now looms as a major threat. Warming ocean temperatures drive prey fish species further north, making it harder for murres to obtain food. Reduced sea ice decreases suitable nesting habitat. Extreme weather can flood nests and separate parents from chicks. Management efforts are needed to prevent extinction.
Conclusion
In conclusion, the deep diving adaptations of the thick-billed murre allow it to plunge to depths exceeding 200 meters in search of prey. No other bird can rival the murre’s routine diving depths. This makes it the world’s deepest diving bird species. However, such extreme dives place physiological constraints on murres and carry risks including decompression sickness. Climate change and overharvest now threaten these remarkable diving seabirds. Increased protection of murres and their habitat may be needed to ensure their survival.
