Cormorants are medium to large seabirds that live along coastlines worldwide. They have short legs, long necks, and hooked bills. Their most distinguishing feature is their short wingspan in proportion to their large body size. Cormorants frequently spread their wings out after diving into water. This behavior has led to an enduring myth that they do it to dry their wings.
Do cormorants spread their wings to dry them?
No, cormorants do not spread their wings after diving specifically for the purpose of drying them. While it may help their wings dry faster, that is not the primary reason they exhibit this behavior. So what is the reason?
Cormorants spread their wings after diving as a thermoregulatory adaptation. Their short wings make cormorants less efficient flyers, but allow them to swim and dive very well. However, the small surface area of their wings means they lose body heat quickly when wet. Spreading their wings exposes the maximum surface area to the air, allowing body heat to evaporate the water and warm their wings and body.
Other reasons cormorants spread their wings
In addition to thermoregulation, there are a few other reasons why cormorants spread their wings after diving:
- To realign feathers – Spreading helps rearrange any feathers that got ruffled while diving.
- To relax muscles – It gives their chest muscles a break after being contracted for diving.
- To dry their gular pouch – This is the stretchy sac of skin under their bill that holds fish they’ve caught.
Cormorant wing anatomy
Cormorants have a unique wing structure that enables them to swim and dive well, but also makes them less efficient fliers.
Their wings have high wing loading, meaning a small wing surface area relative to their body weight. This allows them to swim low in the water and dive easily, but also means they have to work harder to fly.
Some other anatomical adaptations in their wings include:
- Smaller flight muscles than similar sized flying birds
- Stiff feather shafts compared to other waterbirds
- Denser, heavier bones compared to other birds their size
These features minimize the buoyancy of their wings to allow them to dive efficiently. But again, they sacrifice some aerial maneuverability and speed in exchange.
Wing shape
Cormorant wings have a straight leading edge and uneven trailing edge. The pointed wing tips help reduce drag while swimming, but produce less lift for flying.
Lack of oil gland
Most birds have a preen gland or oil gland near their tail that secretes oil. They spread this oil through their feathers as a natural waterproofing. Cormorants lack an oil gland entirely. This means their feathers get soaked during diving, making it even more important for them to spread their wings to dry.
How long do cormorants keep their wings spread?
Cormorants will often spread their wings for anywhere from 10 to 20 minutes after diving. This allows time for their body heat to evaporate most of the water. They may flap their wings periodically to speed up the drying process when needed.
On hot, sunny days they may not need to spread their wings as long. Cool windy days or rough water that requires more flapping may necessitate longer drying times. If they are planning to dive again soon, they will dry their wings for a shorter interval.
Cormorant species differences
There are about 40 different species of cormorants worldwide. They inhabit coastal areas of all continents except Antarctica. Here are some of the key differences between cormorant species:
Species | Location | Distinguishing Features |
---|---|---|
Great cormorant | Coastal Europe, Asia, Africa | Largest size, green-bronze sheen on feathers |
Double-crested cormorant | North America, southern Canada | Orange facial skin, two head crests in breeding season |
Pelagic cormorant | Western North America | Small size, all dark plumage |
Imperial cormorant | Southern South America | Red eyes, blue throat skin |
Spotted shag | New Zealand, southern Australia | Dark bronze sheen, white thigh patches when breeding |
Despite these differences, all cormorant species share common adaptations like small wings, dense bones, and lack of an oil gland. They all spread their wings after diving as a thermoregulatory adaptation.
Cormorant diving and swimming
The small, stiff wings of cormorants enable them to swim low in the water and efficiently pursue fish underwater. Here are some key facts about how cormorants dive and swim:
- They can dive to depths up to 60 meters (200 feet).
- Dives usually last around 30 seconds, but can extend up to a minute.
- Their partially wettable feathers and lack of oil gland allow them to swim lower in the water.
- They propel through the water with their feet, while their wings stay tight against their body.
- They can swim up to 7 km/hr (4 mph) underwater.
Cormorants have excellent underwater vision. Their eyes are well-adapted to seeing in low light conditions. They can discern prey shapes against the muted background light filtering down through the water.
After diving, cormorants will often float along on the surface for a short time while manipulating caught fish into position to swallow head first. This allows time for their buoyancy and oxygen levels to stabilize before diving again.
Plunging versus pursuit diving
Cormorants use two primary diving techniques depending on the circumstances:
- Plunging dives – They dive straight down from the water’s surface. This ambushes unsuspecting fish underneath.
- Pursuit dives – They swim along the surface and dive at an angle to chase escaping prey.
Plunging dives don’t require as much energy, so they will use this method whenever possible. If prey tries to flee along the ocean floor, they will employ an angled pursuit dive instead.
Do other aquatic birds spread their wings to dry?
Cormorants aren’t the only type of waterbird to spread their wings after swimming. However, different birds do it for slightly different reasons:
- Pelicans – Spread their huge wings to thermoregulate and balance their heavy bill.
- Darters – Spread petite wings to realign feathers and signal territorial displays.
- Gannets – Spread long narrow wings primarily to aid internal cooling.
- Grebes – Rarely spread their tiny wings and rely more on feathers for insulation.
The common thread is that most aquatic birds need to dump excess heat after swimming in cold water. But their adaptations are shaped by different evolutionary pressures based on factors like size, diving habits, and proportions.
Conclusion
In summary, cormorants regularly spread their wings after diving, but not specifically to dry them. The primary function is thermoregulation, by evaporating water to cool their body and regain heat lost during swimming. The behavior also helps realign feathers, relax muscles, and dry out their gular pouch.
Their small, stiff wings enable excellent swimming and diving at the cost of aerial agility. When combined with their lack of waterproofing oil gland, it necessitates regularly drying their wings. Next time you see cormorants sitting with outstretched wings, remember they are not just drying off, but regulating their body temperature!