NATURE’S NOTEBOOK

The most widespread cormorant in North America

Double-Crested Cormorant

It’s a common sight along the coastal waters of Southwest Florida—a large black bird resting on a branch, long wings outstretched to soak up the sun. It’s likely a double-crested cormorant (Phalacrocorax auritus), whose plumage is structured for easy underwater hunting, not for repelling water.

The double-crested cormorant is a large, heavy-bodied and dark seabird, ranging from 26 to 32 inches long with a wing span of 4.5 feet. It has a hook-tipped dark bill, orange gular patch and blue eyes. The cormorant can be distinguished from the similar-looking anhinga by its hooked and heavier bill.

The juvenile cormorant has a pale throat and breast, brown upper parts and yellowish gular patch. A 1-year-old cormorant appears dark brown above and tawny underneath.

In flight the cormorant has a rapid wing beat and a strong direct flight. It flies in a goose-like V formation or in a single-file line when traveling between roosting and foraging locations. It swims with its neck and head above water when it’s not swimming underwater hunting for fish.

The cormorant is found throughout most of North America. It can be observed in Florida along both the Gulf and Atlantic coasts, as well as inland. It inhabits open water in both freshwater and saltwater. The Florida subspecies is the smallest. It is common to abundant throughout Florida. During the winter it migrates from northern climes and breeds in Florida. Another subspecies is the great cormorant, which is larger and occasionally can be seen during the winter near east coast inlets.

The cormorant is a colonial breeder with nests found in mangroves, Australian pines, cypress swamps, shrubs and on the ground. Large colonies are found both in inland swamps and coastal islands. It can also be observed nesting in standing dead trees located in phosphate mine impoundments. Nests in

trees can be six to 150 feet above the ground or water. Nesting in Florida can happen at any time of the year, with peak nesting occurring from March through August. The cormorant produces only one brood per year. The earliest breeders are the oldest and most experienced nesters. Their courtship is complex, with the male chasing the female, rapidly swimming in a zigzag motion until his head is submerged and splashing the female vigorously with both wings. The male will also dive and surface with vegetation, then tossing it in the air or just dropping it near the female. Flimsy platform stick nests are built by both sexes with hundreds of other cormorant nests mixed in with many heron and egret nests. Their nests are lined with finer materials. The breeding pairs are monogamous and share incubating duties for 25 to 29 days, tending to three or four bluish-white eggs that are 2.4 inches long. The parents exchange incubation time on the nest every hour or so. The young hatch asynchronously (hatching several days apart from each other). They are altricial in that they are immobile, downless, eyes are closed and they have to be fed. The hatchlings are cared for by both parents until they fledge in 35 to 42 days. The young are brooded continuously for 12 days. They can maintain their body temperatures after 14 to 15 days. The eggs and young are aggressively protected from crows, gulls and other predators. The young are fed regurgitated fish and aquatic invertebrates, offered in a tureen-like bill. The only time a cormorant can be heard is in the breeding colonies. At the nest the adult makes deep, guttural grunts. The cormorant feeds by surface diving or dipping. The microscopic structure of cormorant feathers makes the plumage “wettable” and not water repellant. This decreases buoyancy and aids the underwater pursuit of fish. Hence, the

The microscopic structure of cormorant feathers makes the plumage “wettable” and not water repellant.

cormorant is a fast and efficient swimmer underwater. It will dive as deep as 100 feet to capture and secure fish with its hooked bill. It surfaces to manipulate and swallow its prey. It can swallow large fish, including catfish with large pectoral fins. Some fishermen are not fond of the cormorant as it will try to take their fish before they are landed.

Because of the structure of its feathers, cormorants, like anhingas, are often observed in spread-wing postures drying their wing feathers. This posture for cormorants is just for drying wing feathers, whereas it is also for thermoregulation for the anhinga.

Double-crested cormorant populations seriously declined from the 1800s through the mid-1900s as a result of persecution and introduced predators. Major declines happened again from 1950 to 1970 because of pesticide abuse. Their population has strongly rebounded since 1970 along the Atlantic coast and the interior of North America. There are an estimated 350,000 breeding pairs in North America.