Cormorants are a family of aquatic birds known for their exceptional ability to catch fish. These birds are found globally, inhabiting both coastal and inland waters. Their distinctive appearance, characterized by dark plumage, long necks, and powerful bills, reflects their specialized feeding habits. This article explores what cormorants eat and their hunting techniques.
Main Food Sources
Cormorants primarily consume fish, which constitutes the vast majority of their diet. They are opportunistic predators, targeting species that are abundant and relatively easy to catch in their habitats. This includes a wide variety of small to medium-sized fish, typically those that are slow-moving or bottom-dwelling, such as minnows, perch, carp, eels, and flounders.
The exact composition of a cormorant’s diet can vary significantly based on the species of cormorant, its geographic location, and the seasonal availability of prey. For instance, some cormorants in North America may primarily feed on salmon and salmonids during certain times of the year. While fish are their staple, cormorants also supplement their diet with other aquatic animals.
Secondary food sources include crustaceans like shrimp and crabs, amphibians such as frogs and salamanders, and various aquatic insects. These items are consumed when fish are less available or present an easier foraging opportunity. Smaller cormorant species, for example, might increase their intake of tadpoles and young amphibians during spring and summer breeding seasons.
Hunting Strategies
Cormorants are highly adapted for underwater pursuit, with impressive diving abilities to capture their prey. They can plunge to depths of 150 feet and remain submerged for several minutes, though typical dives are often shallower, ranging from 5 to 25 feet, and last for 30 to 70 seconds. Their streamlined bodies and webbed feet make them powerful and agile swimmers.
Underwater, cormorants propel themselves using their strong webbed feet, while some species may also use their wings for steering. Their distinctive long, thin, and sharply hooked bill grasps slippery fish. Once caught, smaller prey can be swallowed underwater, but larger fish are often brought to the surface to be consumed headfirst.
These birds hunt by visually pursuing individual fish. However, cormorants also exhibit cooperative hunting behaviors, especially when targeting schooling fish. They may work together in groups to herd fish into shallower water or against barriers, making them easier to catch.
Dietary Impact
Cormorants function as natural predators within aquatic ecosystems, regulating fish populations and maintaining ecosystem balance. An adult cormorant eats about one pound of fish per day.
While cormorants consume fish, their overall impact on sport fish populations or commercial fisheries is often localized. Research indicates that cormorants prey on fish species that are not highly valued by recreational or commercial anglers, focusing on smaller, more abundant forage fish. However, in specific situations, such as confined areas or during fish stocking events, their predation can become more noticeable.
Studies suggest that while cormorant predation can be a factor in fish population dynamics, it is often one of many influences, alongside water quality, habitat availability, and other predators. Their diet primarily consists of what is most accessible in their environment.