Cormorants are a widespread group of aquatic birds found globally in diverse aquatic environments. Recognized for their dark, sleek appearance, their distinctive features and behaviors enable them to effectively hunt in both fresh and saltwater habitats.
Distinctive Characteristics
Cormorants exhibit sleek, dark plumage, often iridescent, ranging from black to brown or grey, with some species displaying white patches. They possess long, slender bodies, elongated necks, and a characteristic hooked bill that is well-suited for catching fish. Their fully webbed feet aid powerful underwater propulsion.
A unique physiological aspect of cormorants is their partially non-waterproof feathers. While they have a preen gland that secretes oil, their feather structure allows water to penetrate, reducing buoyancy and enabling more efficient diving. After prolonged dives, this wettability necessitates the birds to perch with outstretched wings to air-dry their plumage. Additionally, cormorants employ a cooling mechanism known as “gular flutter,” where they rapidly vibrate the moist membranes in their throat to dissipate heat through evaporation.
Behavior and Habitat
Cormorants are found in various aquatic habitats worldwide, including coastal areas, large lakes, and rivers, avoiding only the central Pacific islands. They are expert divers, propelling themselves underwater with their powerful webbed feet. Some cormorant species can dive to impressive depths, reaching up to 45 meters (150 feet) and staying submerged for 30 to 70 seconds while pursuing fish.
Their diet consists almost exclusively of fish, which they catch by diving. After fishing, cormorants commonly perch on rocks, trees, or other elevated structures with their wings spread wide. These birds are highly social, often nesting in large colonies on cliffs, trees, or islands, and communicating through various vocalizations.
Cormorants and Their Environment
Cormorants play a role as predators within aquatic food webs, consuming fish species, primarily those that are abundant and easy to catch. Their populations have largely recovered after declines in the mid-20th century, partly attributed to pesticides like DDT. Today, several cormorant species are classified as “Least Concern” on the IUCN Red List, with increasing or stable populations.
The relationship between cormorants and humans, particularly fisheries, has been complex. While their populations have thrived, their efficiency at catching fish has sometimes led to conflicts with commercial and recreational fishing interests. Despite these localized concerns, cormorants are an integral part of many aquatic ecosystems.