In coastal and freshwater environments of many regions around the world, a large black bird has captured the attention of fishermen and researchers for its remarkable abilities in diving and fishing🧐.
The Great Cormorant, 𝘗𝘩𝘢𝘭𝘢𝘤𝘳𝘰𝘤𝘰𝘳𝘢𝘹 𝘤𝘢𝘳𝘣𝘰 (Linnaeus, 1758), is mainly found in the Old World and east of North America. The species is a common winter visitor in Hong Kong, migrating south from breeding grounds in North Korea. It mainly inhabits shallow water areas, such as coasts, lakes and rivers. They have a large body size, with adult individuals having a wingspan of 130-160 cm. Sporting a sleek black plumage, the Great Cormorant is a sight to behold🌚. This bird uses a distinctive hunting method. Instead of quickly snatching fish from the surface like kingfishers or egrets, they dive directly into the water to catch their prey. They can hold their breath for up to 28 seconds and reach depths of up to 5.8 meters underwater🤿.
In the avian world, waterproof feathers are the norm, thanks to a specialized oil (preen oil) secretion from a gland at the base of the tail called the uropygial gland. Most birds rely on this oil to keep their feathers dry and maintain their body temperature. The Great Cormorant, a true underwater specialist, however, defies this « convention ». In fact, they don’t spread oil on their feathers❌🧈 but instead, by keeping them free of oil, the Great Cormorant allows them to easily absorb and retain water while diving. This intentional saturation increases its body density, reducing buoyancy and facilitating effortless dives into the water. It's a bit like donning a natural wetsuit ! However, as they come out of the water, the wet feathers become a hindrance. But fear not, this bird species has a solution. It takes to the rocks or perches on tree branches, stretching its wings wide open, exposing them to the air and sunlight. This behavior, known as "wing drying," helps the bird to quickly dry its feathers, restoring its ability to fly and stay warm🌞.
They also possess exceptional agility underwater. To make it easier for them to swim quickly underwater, they developed webbed toes to increase the surface area, which increases the propulsive drag with each stroking. The webbed toes also act as a rudder to control the swimming direction. These adaptations allow them to navigate with precision, swiftly pursuing its fish beneath the surface🦆.
But how does the Great Cormorant manage to locate its prey underwater? Its vision is blocked underwater, so it has evolved unique auditory adaptations. They have a two-layered eardrum which is thick enough to resist water pressure. Studies also found that their ear structures are more sensitive in water, enabling these birds to detect underwater sounds more effectively🌀. These specialized ears provide the Great Cormorant with an auditory advantage, allowing it to pinpoint the movements of fish and strike with unerring accuracy. So in fact, their hearing ability underwater is better than their hearing ability in the air.
Come see life-size specimens of the great cormorant at the Hong Kong Biodiversity Museum. You can try calling it, maybe it will say “I can’t hear you !”
Text: Long
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