Cormorants often work cooperatively to catch fish Lack of body oils means easier underwater swimming

A strong onshore breeze ruffled the sea’s surface as I walked along the beach late one recent afternoon. The partly overcast sky colored the ocean a gun-metal gray, a reminder that fall really is here to stay, a few 80-degree days notwithstanding.

The tide was falling. I noticed the few exposed rocky ledges were occupied by double-crested cormorants, big birds that look ungainly when out of the water.

A few of the birds were resting quietly, while another stood with its wings spread wide from its body, periodically giving them a little shake. I’d seen this comical-looking posture adopted often by these birds and learned its function serves to dry the feathers.

Unlike most other birds, a cormorant’s plumage can become somewhat waterlogged; it is not as protected by a coating of its own body oils. This decreases their buoyancy in the water and allows them to swim and dive with ease. This feature, along with powerful webbed feet, also enables them to pursue their prey – which often consists of small, quick, and agile fish – entirely underwater.

Cormorants often work cooperatively when hunting. E.V. Glanville, writing for a 1992 issue of the Canadian Field Naturalist, described groups of up to 175 birds driving fish into the heads of narrow bays. Other observations I’ve come across have noted cormorants herding fish in conjunction with pelicans, which must be quite an impressive sight.

Cormorants are easy to identify when seen swimming on the water’s surface. They swim very low in the water, so low that only their heads and necks appear above the surface at times. They also have long, sinuous necks; these two traits will reliably distinguish them from other water birds such as loons.

Young double-crested cormorants differ from adults in plumage. Whereas adults are glossy black, juveniles most often have a light brown back, neck, and head, and a pale underbody.

Interestingly, these birds incubate their eggs by rolling them on top of their webbed feet, which are warm; they then lower themselves down over the eggs, covering them with their breast and belly feathers. While this may seem to be a very secure method of incubation, this actually isn’t the case when the birds are flushed from the nest because when this happens, the eggs are often flung out of the nest as the parent takes flight. However, they seem to have adapted to this eventuality by quickly laying another set of eggs, according to the “Birds of North America” species account.

Humans have long viewed (and persecuted) cormorants as competitors for fish harvests, but it has never been proven that they have a significant impact on wild fish populations, according to the BNA. However, cormorants do take advantage of fish farms and will readily exploit such easily captured prey.

As I watched the cormorant dry its wings that day, I realized I had gotten used to seeing them throughout the summer and into the fall. Soon they’d be migrating to points farther south, and I realized I’d miss their ubiquitous presence. However, their impending absence brings with it the anticipation of wintering sea ducks and other birds, so I’m looking forward to our upcoming seasonal visitors.

BDN bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net