When I walk along Boston Harbor, I love seeing birds flying and swimming in the water. One of my favorites is a bird with an iconic pose: the cormorant.
38 different species of cormorants and shags make up the cormorant family Phalacrocoracidae. They are coastal birds found across the world, with long, thin, sharply hooked beaks. Cormorants nest in colonies along the coasts, using trees, rocky islets, or cliffs as spots for their nests.
The name “cormorant” comes from the Latin corvus marinus, or “sea raven,” as people erroneously believed that cormorants were related to ravens. They are, in fact, more closely related to pelicans.
Swimmers
Every species of cormorant eats fish and hunts by diving underwater. Like other aquatic birds, cormorants have webbed feet to propel them through the water.
Cormorants have also evolved to be extremely dense, making them about the same density as the surrounding water when they’re diving for fish. This helps them focus their energy on swimming after fish since they don’t have to spend energy fighting to stay underwater. Cormorant feathers also don’t have much water-repellant oil, keeping them from retaining air and pulling the cormorant up to the surface.
Cormorants can dive deep under the water to catch their prey. One species has even been recorded diving as deep as a 13-story building is tall. Once underwater, cormorants zip around catching fish. One bird was even seen pulling remoras (suckerfish) off of a whale shark.
Unfortunately, a cormorant’s underwater optimization means flying is difficult, particularly take-off. Cormorants typically start by running across the surface of the water while flapping their wings to gain speed. Once airborne, they initially stay close to the water to gain some additional lifting pressure from the downbeat of their wings reflecting off the water surface.
Iconic Stance
Cormorants are known for their characteristic posture when standing on a river bank or dock: facing the sun with their wings outstretched. But why do they stand like this?
Remember how cormorant feathers don’t produce much water-repellant oil? This comes at a cost: wet feathers. Basking in the sun is likely a way to dry themselves off. It also doesn’t hurt that it feels nice to get warm in the sunlight!
Cormorants in Boston
The cormorant I see in Boston in the summer is the double-crested cormorant, the most common of the six cormorant species in North America. But had I been living in Boston 150 years ago, I wouldn’t have seen any cormorants at all.
Humans, mainly fishermen, often view cormorants as threats. Cormorants nest in colonies, and the large accumulation of feces can kill trees and vegetation. Cormorants also seem to be in direct competition with fishermen for fish, although research has shown that they have less impact on the local fish population than people think. Since colonial times in New England, people have been hunting cormorants to protect their fishing livelihood. By the early 1800s, cormorants had been completely removed from the area.
But we couldn’t keep double-crested cormorants out of Massachusetts for long: breeding pairs returned by 1944, and colonies have continued to grow. By the 1990s, approximately 8,000 pairs of birds were nesting at 25 different breeding sites. Starting in September, double-crested cormorants migrate out of the region for the winter and are replaced with great cormorants.
Fishing!
For as long as humans have decried cormorants for stealing our fish, we’ve also taken advantage of their fishing skills. In places like China, Japan, and Macedonia, cormorants were trained to catch fish for human fishermen. Before fishing, a rope is tied near the base of the cormorant’s throat. While the cormorant can still swallow small fish, larger fish get stuck. This is when the cormorant returns to the fishing boat, where the fisherman removes the fish.
Cormorant fishing is much less common today since there are more efficient ways of catching fish. Still, you can see traditional cormorant fishing in places like Gifu City in Japan, where cormorant fishing has continued for 1300 years!
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