Cormorants are medium-sized waterbirds that can be found near bodies of water across the world. They are very skilled divers and swim completely submerged to catch fish and other aquatic prey. Cormorants have a number of adaptations that allow them to dive deep underwater in search of food. In this article, we will explore how far down cormorants can dive and examine the adaptations that allow them to be such efficient underwater hunters.
Quick Facts on Cormorant Diving
- Cormorants can dive to depths of up to 45 meters (150 feet).
- The average diving depth is around 14 meters (45 feet).
- Cormorants have solid bones unlike most other diving birds which have air sacs in their bones.
- Their feathers are not waterproof, so they rely on preen oil to reduce water penetration.
- Powerful feet and sharp beak allow them to easily grasp slippery prey.
The cormorant’s ability to dive deep makes it well suited to catch fish, eels, crustaceans and other food. Their wing shape also enables them to swim and maneuver quickly when pursuing prey underwater. Now let’s look in more detail at how the anatomy and physiology of cormorants allow them to excel at deep diving.
Cormorant Anatomy and Physiology for Diving
Cormorants have a number of special adaptations that enable them to dive efficiently to catch prey:
Dense Bones
Most diving birds have hollow air sacs in their bones to help them float on the surface. Cormorants have mostly solid bones which make them less buoyant, allowing them to swim and dive more easily. The higher bone density gives them ballast underwater.
Powerful Feet for Swimming
A cormorant’s feet have strong webbing between the toes. This webbed foot structure combined with strong leg muscles give them powerful propulsion to swim after fast-moving fish. Their long, narrow beak is also hook-shaped at the end to snatch up slippery prey.
Wettable Plumage
Unlike aquatic birds like ducks, a cormorant’s feathers are not waterproof. This means that water penetrates through their plumage rather than being repelled. The wet feathers reduce buoyancy, enabling the cormorant to swim low in the water rather than floating higher on the surface.
Preen Oil
Since their feathers get soaked, cormorants produce preen oil from a gland near their tail to coat their feathers. This oil helps reduce water penetration and retains heat and buoyancy better than if their feathers were completely soaked.
Short Wingspan
Cormorants have proportionately short, stubby wings relative to their body size. This helps reduce drag underwater so they can propel forward more efficiently. Their short wingspan also enables them to maneuver around rocks and seaweed on the seabed as they chase prey.
Eye Adaptations
A cormorant’s eyes are well adapted for seeing underwater. They have excellent underwater vision and are able to focus through their flat cornea. A clear membrane covers and protects their eyes while diving.
Body Profile
A cormorant’s body profile is optimized for diving. They have a long neck, streamlined head, and tapered bill that reduces drag as they swim rapidly after fish underwater. Their feet are set far back on their body to provide greater thrust.
Maximum Diving Depths
So just how deep can cormorants dive down below the water’s surface? Here’s an overview of the maximum and average depths:
Maximum Depth: Up to 45 meters (150 feet)
Typical Diving Depth: Around 14 meters (45 feet)
The depth a cormorant can reach depends on the species as well as other factors like water temperature, salinity and available prey at different depths.
Some of the deepest diving depths recorded for different cormorant species include:
Cormorant Species | Maximum Recorded Dive Depth |
---|---|
European Shag | 60 m (197 ft) |
Blue-eyed Shag | 40 m (131 ft) |
Great Cormorant | 40 m (131 ft) |
Japanese Cormorant | 36 m (118 ft) |
Pelagic Cormorant | 30 m (98 ft) |
As the table shows, some species like the European Shag have been recorded diving to depths approaching 60 meters when pursuing prey. However, the typical diving depth for most cormorant species appears to be around 14 meters or less.
Dive Duration
In addition to diving deep, cormorants can also remain underwater for extended periods while hunting before returning to the surface. Some key facts on cormorant dive duration:
- Can stay submerged for over a minute while pursuing prey.
- Most dives are 15-30 seconds.
- They dive, swim and catch prey completely submerged.
- Cormorants resurface before running out of oxygen to breathe.
Cormorants are able to maximize their time underwater and oxygen use by reducing their heart rate and blood flow to selected organs when diving. This helps prolong their time below the surface and expend less energy as they chase after fish.
Here are some observed dive durations for different cormorant species:
Cormorant Species | Maximum Dive Duration |
---|---|
Great Cormorant | 48 sec |
Japanese Cormorant | 41 sec |
Pelagic Cormorant | 68 sec |
In general, cormorants rarely exceed dive durations of one minute. More often their dives are 15-30 seconds when actively pursuing schooling fish or seabed-dwelling prey at depth.
Underwater Hunting Adaptations
Cormorants have a number of behavioral and physical adaptations that enable them to dive and hunt effectively underwater:
Swim Completely Submerged
Unlike some diving birds, cormorants swim fully below the surface when pursuing prey instead of jumping and diving from the air above. This stealthier approach likely helps them surprise and ambush fish underwater.
Swift Underwater Swimming
Using their webbed feet for propulsion, cormorants can reach fast burst swimming speeds to chase down free-swimming fish. Their streamlined shape and flexible neck enable quick acceleration.
Sharp Vision
Excellent underwater eyesight allows cormorants to spot prey from a distance even in dark or murky water conditions. Their eyes are adapted to swiftly focus when transitioning between air and water.
Grasp Prey Securely
The hooked shape of a cormorant’s bill enables it to snatch up slippery fish and eels effectively. Their bill also has a hinge that allows them to get a firm grip on prey.
Store Prey
After catching fish underwater, cormorants often store prey temporarily in a throat pouch below their bill to free up their mouth. This allows them to continue hunting without having to return immediately to the surface.
Cormorant Species
There are approximately 40 different species of cormorants around the world. Some of the major species and their diving abilities include:
Great Cormorant
Common across Europe, Asia and Africa. Can dive to depths over 30 m and chase fast-moving fish like salmon. Often hunts near the seabed in estuaries and harbors.
Japanese Cormorant
Found around Japan’s coasts. Skilled at diving in shallow, inshore waters to catch small fish and invertebrates. Maximum recorded dive of 36 m depth.
Red-faced Cormorant
Located off southern Australia and New Zealand. Dives from the surface to pursue schooling fish. Has an average diving depth around 14 m.
Pelagic Cormorant
Distributed along the Pacific coast of North America. Can plunge to depths of over 30 m to catch bottom-dwelling fish. Maximum dive time of 68 seconds recorded.
European Shag
Resides along rocky coasts of Western Europe. Can reach depths up to 60 m and often brings back large fish like sand eels and wrasses.
Diving Differences Among Species
The diving abilities of cormorant species vary based on the size of the bird, habitat, and type of prey they hunt:
- Larger cormorant species can generally dive deeper than smaller ones.
- Some species are optimized for shallow dives in harbors and kelp forests.
- Cormorants that hunt schooling midwater fish dive differently than those taking bottom fish.
- Water temperature and clarity impact accessible diving depths.
These differences highlight how diverse cormorant species have adapted to their local environments and prey. However, across all species, the common thread is having robust diving skills to hunt underwater.
Diving Behavior Throughout the Day
Cormorants tend to follow predictable daily patterns in their diving activity:
- Most dives occur in early morning and late afternoon/evening.
- Midday hours have less diving when fish move to deeper, darker waters.
- Forage mainly in shallow waters at night.
- Dive depth gets deeper as day progresses following fish schools.
These diving patterns likely match the daily movements and availability of the fish, crustaceans and other prey in their local habitat. Prime feeding times coincide with when prey is closer to the surface and easier to catch.
Comparison to Other Diving Birds
How do cormorant diving abilities compare to other underwater diving birds? Here is an overview:
Penguins
Can dive deeper on average than cormorants, with emperors and king penguins reaching 130-500 m depths. But penguins hunt different prey like squid and have different wing anatomy.
Gannets
Plunge dive from the air up to 30 m depth. Less optimized for underwater swimming than cormorants. Hunt larger prey like herring.
Auks
Smaller alcids like puffins and guillemots dive from the surface to around 60-80 m to catch fish and invertebrates. Have higher metabolisms than cormorants.
Ducks
Most duck species only dive to several meters depth at most. Do not swim fully submerged or have adaptations for deep diving.
Shearwaters
Pursuit divers that can reach 70 m depth. Use underwater wing flapping to propel unlike the foot paddling of cormorants.
Overall cormorants appear uniquely specialized among diving birds for swimming completely submerged to substantial depths of 40-50+ meters in pursuit of fish. Their robust diving skills enable them to thrive around the world from coastal to freshwater habitats.
Conclusion
Cormorants are highly impressive divers, using their dense bones, wettable plumage, webbed feet and other adaptations to routinely dive to depths of 10-45 meters while hunting. Different species have evolved to take advantage of local prey, with some like the European Shag recorded reaching 60 meter depths. While penguins and other diving birds may reach greater maximum depths in some cases, cormorants stand out for their ability to propel fully underwater and navigate into hard-to-reach rocky terrain and kelp beds. Their specialized diving skills showcase the remarkable aquatic adaptations of seabirds. Clearly the cormorant deserves its reputation as one of the most capable diving birds.