Cormorants are aquatic birds that are experts at catching fish. They have a number of special adaptations that allow them to effectively hunt and swallow fish. Cormorants have long, hooked bills that they use to catch fish. Their bills are hinged in a way that allows them to open their mouths very wide to accommodate large fish. Once a cormorant catches a fish in its bill, it tosses it into the air and swallows it headfirst. Cormorants have expandable throat pouches called gular skin that allows them to swallow fish much larger than the diameter of their throats. Their digestion is very rapid and efficient so they can eat dozens of fish per day. Read on to learn more details about how cormorants use their specialized anatomy to successfully hunt and consume fish.
Hunting Adaptations
Cormorants have a number of specialized features that aid their fish hunting abilities:
Serrated Bill
Cormorants have long, hooked bills with jagged edges and a sharp tip. This allows them to securely grasp slippery fish. The serrated edges of their bill help them get a firm grip on fish.
Quick Strike
Cormorants are able to strike with lightning speed when they see a fish, helping them catch fast swimming prey. Their flexible necks allow them to dart their heads quickly to grab fish.
Webbed Feet for Diving
Cormorants have webbed feet which they use to powerfully propel themselves underwater while pursuing fish. Their feet are placed far back on their bodies, near their tails, which provides maximum thrust. Cormorants can dive to depths of 30 meters in search of fish.
Waterproof Plumage
A cormorant’s feathers are not water logged like many water birds. They have a fine, dense coat of contour feathers that repel water. This allows cormorants to swim and dive freely without becoming weighed down by soaked plumage.
Swallowing Adaptations
Once a cormorant has caught a fish in its bill, it must swallow it. Cormorants have several special adaptations that allow them to swallow large, wriggling fish:
Extensible Throat and Neck
Cormorants have long, extendible necks which allows them to reach forward and use their bills to manipulate fish into position for swallowing. Their throat pouches are also very expandable, allowing fish much wider than their throat to be consumed.
Backward-Facing Spines on Tongue
The tongues of cormorants have sharp spines pointing towards the back of their throats. This helps prevent fish from wriggling forward and escaping once swallowed. The spines keep fish securely in place as they are consumed.
Rapid Swallowing Reflex
Cormorants swallow extremely quickly, often in less than a second. Their reflexes are specially adapted to getting fish down their throats rapidly before the prey can escape. This swift swallowing motion is aided by their flexible necks.
Gular Pouch
Perhaps the most important adaptation cormorants have for swallowing fish is their gular pouch. The gular pouch is an expandable section of skin on their throat that allows the throat diameter to expand greatly while swallowing, enabling cormorants to consume very large fish.
Swallowing Process
The actual process a cormorant uses to get a fish from its bill into its stomach is fascinating:
Tossing the Fish
After catching a fish tightly in its bill, the cormorant will fling it into the air above its head. This tosses the fish into position for swallowing and disorients it to prevent escape.
Positioning the Fish
As the fish falls back towards the cormorant’s gaping bill, the cormorant will grab the fish mid-air and manipulate it to align headfirst in its throat. Cormorants always swallow fish starting with the head.
Opening the Gular Pouch
Just before swallowing, the cormorant expands its gular pouch, greatly widening the opening of its esophagus to accommodate the width of the fish. This enables it to swallow the fish whole.
Powerful Swallow
The cormorant uses its extendible neck muscles to make a swift, single contraction motion that draws the fish down its throat and into its esophagus in less than a second. This rapid motion overcomes the fish’s attempts to wriggle free.
Returning to Normal
Immediately after swallowing, the cormorant’s gular pouch recedes, returning its throat to normal size. The fish passes through the cormorant’s esophagus on the way to its stomach.
Other Swallowing Adaptations
In addition to their expandable gular pouches, cormorants have some other helpful adaptations to aid in swallowing fish:
Short, Wide Esophagus
Cormorants have a wide, short esophagus rather than a long, narrow one. This reduces the distance fish have to travel during swallowing, giving them less time to attempt escape.
Excellent Eyesight
Keen eyesight helps cormorants accurately grab fish mid-air while positioning them for swallowing. Their eyes are specially adapted to see clearly underwater as well while hunting.
Rotatable Head and Neck
The ability to freely rotate their neck over 270 degrees in any direction allows cormorants greater flexibility while positioning fish for swallowing.
Single Point Entry Esophagus
A cormorant’s esophagus connects to the lower mandible of its bill rather than the upper. This positions fish perfectly aligned for quick swallowing.
Diet and Hunting Habits
Cormorants are exclusively piscivorous, meaning fish make up their entire diet. A typical cormorant eats 1 to 2 pounds of fish per day. They exhibit a number of hunting and feeding behaviors and preferences:
Types of Prey
Fish Type | Examples |
---|---|
Small schooling fish | anchovies, herring, smelts |
Freshwater fish | perch, trout, bass, sunfish |
Bottom-dwelling fish | flounder, sculpin, sole |
Hunting Locations
- Open water
- Along rocky coasts
- Near estuaries
- Freshwater lakes and rivers
Foraging Dives
Cormorants may dive 30 feet or more underwater in search of fish. Their dives last around 30 seconds on average.
Solitary and Group Foraging
Cormorants hunt both alone and cooperatively in groups. Flocks of cormorants diving together can herd fish into dense bait balls.
Disgorging Food for the Young
Cormorant parents feed their chicks by catching fish, swallowing them, partially digesting them, then regurgitating the food into the chicks’ mouths.
Unique Physiology
Beyond their physical adaptations for hunting and swallowing fish, cormorants have some other interesting physiological traits:
Wettable Plumage
While a cormorant’s contour feathers are waterproof, their wing and body feathers are not. This makes it easier for them to dive by reducing buoyancy but means they must dry their wings after fishing.
Dense Bones
A cormorant’s bones are more dense than other birds, weighing them down in the water to aid in diving. Their feet are also bigger relative to their body size to power underwater propulsion.
Unihemispheric Slow-Wave Sleep
Cormorants can sleep with half their brain awake at a time. This allows them to float in the water yet still rise to breathe without fully waking up.
Blue-Green Eyes
Cormorants have striking light blue or green colored eyes. It’s thought this aids their vision when hunting underwater.
Long Life Span
The average life expectancy for a cormorant in the wild is about 10 years. The oldest known cormorant lived to 36 years old.
Ecological Role
As expert fishers, cormorants play an important role in the food webs of their aquatic ecosystems:
Population Control
By preying on many smaller fish, cormorants help keep fish populations in balance and prevent overpopulation.
Nutrient Distribution
Their droppings contain nutrients from fish that can fertilize aquatic vegetation and redistribute nutrients between land and water.
Bioindicators
As fish-eating birds, cormorants are sensitive to pollution and other ecosystem changes, serving as an indicator species for the health of waterways.
Threats and Conservation
Some cormorant populations face threats from human activity:
Fisheries Conflicts
Cormorants’ diet overlaps with popular game fish pursued by anglers, leading to persecution by humans in some areas.
Habitat Destruction
Wetland drainage and destruction of nesting sites threatens breeding colonies. Water pollution can reduce their food supply.
Climate Change
Rising sea levels may flood coastal nesting sites. Prey populations may also shift due to changing ocean conditions.
Conservation Efforts
Outreach, legal protections, sustainable fisheries management, and habitat conservation are key to ensuring cormorants remain part of healthy, stable ecosystems.
Conclusion
Cormorants are remarkably well adapted for their specialized piscivorous lifestyle. Their impressive fish swallowing abilities rely on expansive gular pouches, swift neck motions, backward-facing tongue spines, and coordination to precisely manipulate prey. Cormorants fill an important niche in aquatic habitats, and ongoing conservation efforts aim to prevent overexploitation of these iconic fishing birds by humans. Their unique hunting skills and biology continue to fascinate both scientists and nature lovers alike.