northeast naturalist: Cormorants

Cormorants – © Dave Spier

If you’re a fisherman, “cormorant” is likely a four-letter word. I suppose there are a few people other than birders who love them, but most probably don’t care one way or the other.

Cormorants are large, dark birds that can be mistaken for geese when flying. Young birds are pale underneath with an orange bill and face. When swimming, the bill is raised at an angle. At close range, you can see the small hook on the bill tip. Nicknamed the “sea-crow” along the coast and “water turkey” inland, the common Double-crested Cormorant (Phalacrocorax auratus) gets its name from two tufts of feathers on the sides of the head just behind the eyes. The feathers curl around and meet at the back, but they are often matted down and resemble a bump.

Cormorants are adept at both flying and diving. Normally these activities require opposite adaptations, such as light-weight versus heavy. The cormorant has evolved feathers that lack the waterproofing of other diving birds, so they become heavier underwater. This allows them to submerge and catch fish, their primary diet, but once they’re done feeding, cormorants must find a perch to spread and dry their wings. It’s common to see them sitting upright on a dock, piling or stump with their wings outstretched. This is also the reason they must head south for the winter. Florida and Alaska’s Aleutian Islands are the Double-crested Cormorant’s only year-round range.

Cormorants are widespread across the continental United States with the heaviest concentrations on all the coasts plus the Great Plains, lower Mississippi Valley and Great Lakes. Check eBird for a current range map.

In some areas their population growth has been explosive which can affect local fisheries and fish farms. Fishermen have blamed them for declines in musky, Largemouth and Smallmouth Bass, Yellow and White Perch, and Walleye. An old stomach-content survey of cormorants, done over a two-year period in all four seasons, showed the birds predominantly prey on small minnows, including shiners, flatheads and dace. Directly ingesting game fish amounted to less than 5% of their diet, and that was limited to late summer. That leaves the potential problem of reducing the bait supply, but in areas like west-central New York, where the water is either weedy or deep, the minnows have plenty of hiding cover. It’s only along shorelines like the east end of Lake Ontario, where the water is shallow and relatively clear, that there is a real conflict.