Identification | Biology | Damage ID | Management | Resources
Cormorants are slender birds with webbed feet and a long
sturdy beak with a hook at the end. Six species reside in North America, namely
the great cormorant (Phalacrocorax carbo),
double-crested cormorant (Phalacrocorax
auritus; Figure 1), neotropic cormorant (Phalacrocorax brasilianus), red-faced cormorant (Phalacrocorax urile), pelagic cormorant
(Phalacrocorax pelagicus), and
Brandt’s cormorant (Phalacrocorax
This module will focus on the most populous and widely dispersed cormorant, the double-crested cormorant.
The double-crested cormorant is a long-lived, colonial-nesting water bird native to North America. It usually is found in flocks, and sometimes confused with geese or loons when on the water (Table 1).
Double-crested cormorants have black plumage tinted with a greenish gloss on the head, neck, and underside. In breeding plumage, tufts or crests of feathers appear for a short time on either side of the head of adult birds, giving them their name. Their black bills are slender and cylindrical with a hooked tip and sharp edges. They have black, webbed feet set well back on their body, a long curving neck, orange facial skin, and an orange throat pouch like their pelican relatives (family Pelicanidae). Some 1- to 2-year-old juvenile cormorants may have grey or tan plumage on their neck and breast.
Double-crested cormorants have a body length of 29 to 36 inches, a wingspan of about 54 inches, and weigh 4 to 6 pounds. On average, double-crested cormorants live for about 6 years, but 19-year-old birds have been documented in the wild.
The great cormorant is the largest of the cormorants and can weigh over 7 pounds. Juveniles will have a brown neck and white belly. Adults will have a white throat and black head. During breeding season, adult head plumage will develop white streaks radiating from the throat.
The great cormorant resides on the east coast, preferring saltwater habitats. The double-crested cormorant has the largest range, with it being found in watered areas across the continental US and along the southern coast of Alaska (Figure 2). The neotropic cormorant lives in coastal Texas, and the red-faced cormorant, pelagic cormorant, and Brandt’s cormorant reside on the west coast of the US.
Although double-crested cormorants are widespread, some geographic areas have experienced significant population growth and conflict. The breeding range of the cormorant is divided into 5 geographic areas—Alaska, the Pacific coast, the southern United States, the interior United States and Canada, and the northeast Atlantic coast. Populations have been growing and expanding since at least the 1980s in the interior United States and Canada, northeast Atlantic coast, and the southern United States.
Within the interior United States and Atlantic coast regions, the occurrence and severity of cormorant impacts varies. For example, in the Great Lakes region, the number of cormorants increased an average of 29 percent per year from 1970 to 1991, after which population growth slowed. In some of these areas, cormorant populations may be at an all-time high. However, recent population increases may alternatively represent recovery toward pre-settlement numbers of cormorants in some regions, and a re-colonization in other regions after a long period of absence resulting from pesticide contamination and shooting.
Recent population increases follow a dramatic population decline that occurred between the 1950s and 1970s, caused by the effects of human persecution, and chemical contamination from DDT. Cormorant numbers began to rebound in the mid-70s when DDT was banned. Pollution control lowered the concentrations of toxic contaminants in the bird’s food. Food became more abundant throughout their winter and summer ranges (especially associated with the southern catfish industry), and cormorants were given protection by both federal and state laws. This combination of factors allowed populations of these adaptable birds to grow rapidly, and conflicts developed with the aquaculture and sport-fishing industries.
Voice and Sounds
When away from the roost, they usually are silent, but they may make hoarse, grunting alarm notes at roost sites.
Tracks and Signs
Cormorants have webbed feet, but rarely leave tracks on the rocky substrate used for nesting. The most obvious signs are visual observations of flocks of birds feeding or resting, or their coarsely-constructed stick nests.