Cormorants are slender birds with webbed feet and a long sturdy beak with a hook at the end. Six species reside in North America:
- 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 penicillatus).
This page will focus on the most populous and widely dispersed cormorant, the double-crested cormorant.
The US Fish and Wildlife Service (USFWS) has the primary responsibility and authority for managing migratory bird populations in the United States. This authority was established by the Migratory Bird Treaty Act of 1918, a treaty between the United States and Great Britain (on behalf of Canada) to:
- ensure the conservation and management of migratory birds internationally
- sustain healthy migratory bird populations for consumptive and non-consumptive uses and
- restore declining populations of migratory birds.
In 1972, the US Convention with Mexico was amended and the double-crested cormorant was added to the list of Migratory Birds and given protection in the United States under the Migratory Bird Treaty Act. Under this protection, cormorants cannot be captured or shot, and their nests and eggs cannot be disturbed unless a permit is first obtained from the USFWS.
Depredation permits to take cormorants have been issued by USFWS since 1986 and may allow for the taking of eggs, adults, young, or active nests.
USDA APHIS Wildlife Services
Although the USFWS has primary responsibility for managing cormorants, the USFWS does not conduct on-the-ground management activities when cormorants cause damage. The US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services (WS) is the primary federal agency involved with on-the-ground management. Their job is to help states, organizations, and individuals resolve conflicts between people and wildlife on public and private lands by collecting information, documenting damage, and recommending or implementing options for wildlife damage management.
In March 1998, the USFWS issued an Aquaculture Depredation Order, allowing people engaged in commercial aquaculture to shoot cormorants without a federal permit at freshwater aquaculture facilities, or state-operated hatcheries in Minnesota and 12 southeastern states. The Depredation Order allowed shooting of cormorants during daylight hours when necessary to protect aquaculture/hatchery stock, if these actions were taken in conjunction with a non-lethal harassment program approved by WS.
State Wildlife Management Agencies
State wildlife management agencies also are actively involved in management of double-crested cormorants. In many states, double-crested cormorants are protected by state migratory bird legislation in addition to the Migratory Bird Treaty Act. Cormorant control programs are being implemented in states where birds are negatively affecting fish populations, vegetation, and other colonial water-birds. In New York and Vermont, for instance, programs are underway to prevent the spread of cormorants to other nesting islands in Lake Ontario, Oneida Lake, and Lake Champlain. Until recently, a federal permit issued by the USFWS was required before any state agency could implement a control program. As populations of cormorants in many states increased, the existing permit requirements left little flexibility for states to efficiently deal with conflicts on a local level.
In 1999, the USFWS with WS as a cooperator, recognized the need to respond to new challenges facing resource managers, and began developing an Environmental Impact Statement (EIS) on double-crested cormorant management “to address impacts caused by population and range expansion of the double-crested cormorant in the United States.” This document, approved in 2003, was developed to address growing concerns from the public and natural resource management professionals about the effects of double-crested cormorants on local fish populations, other bird populations (including threatened and endangered species), vegetation and habitat, private property, and economic opportunities. The goal of the EIS was to develop management options to reduce conflicts with double-crested cormorants and enhance the flexibility of land management agencies to deal with problems on a more local level, while ensuring the long-term sustainability of cormorant populations.
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.
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.
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.
When away from the roost, cormorants are usually silent, but they may make hoarse, grunting alarm notes at roost sites.