Brian S. Dorr 

Research Wildlife Biologist 

USDA-APHIS-Wildlife Services 

National Wildlife Research Center 

Mississippi State, Mississippi 

 

Kristi L. Sullivan 

Extension Associate 

Department of Natural Resources 

Cornell University 

Ithaca, New York 

 

Paul D. Curtis 

Associate Professor 

Department of Natural Resources 

Cornell University 

Ithaca, New York 

Richard B. Chipman 

Rabies Management Program Coordinator 

USDA-APHIS-Wildlife Services 

Concord, New Hampshire 

Russell D. McCullough 

Regional Fishery Biologist 

New York State Department of Environmental Conservation 

Bureau of Fisheries 

Albany, New York

Human-Wildlife Conflicts

Fisheries

The history of conflict between doublecrested cormorants (Figure 1) and human 

interest in fisheries is long and convoluted. 

Following a low point in the 1970s, 

populations of cormorants expanded in 

North America, as did concerns about 

impacts on fisheries. By the late 1990s, 

natural resource agencies in 27 states 

reported losses of free-ranging fish stocks 

to cormorants. Agencies in 10 states, 

ranging from the Southwest to the 

Northeast, considered cormorant 

predation to be of moderate to major 

concern to fishery management. 

Wildlife Damage Management 

Technical Series

U.S. Department of Agriculture

Animal & Plant Health Inspection Service

Wildlife Services

August 2016 Double-crested 

Cormorants

Figure 1. Double-crested cormorant 

(Phalacrocorax auritus)

Quick Links

Human-Wildlife Conflicts 1

Damage Identification 3

Management Methods 4

Economics 9

Species Overview 9

Legal Status 13

Glossary & Key Words 15

Resources 16 

Appendix 17 
Overall, double-crested cormorants are not major 

consumers of commercial and sportfish species. However, 

exceptions have been recorded at specific sites with 

documented impacts on local fisheries (see Damage to 

Fisheries section). Cormorants often congregate and can 

have significant local impacts where high concentrations of 

fish occur, such as stocking release sites, private fishing 

ponds, aquaculture ponds, reservoirs, spawning sites, and 

other areas. 

Landscapes 

Double-crested cormorants can have a significant impact 

on vegetation at breeding sites through normal nesting 

activities. Their guano is acidic and can change soil 

chemistry, killing ground vegetation and irreversibly 

damaging nest trees. Cormorants also destroy vegetation 

directly by stripping leaves and small branches from trees 

for nesting material. At times, the weight of the birds and 

their nests can even break branches. Loss of trees can 

lead to increased erosion, particularly on sand spits and 

barrier beaches. 

In one example on Little Galloo Island in Lake Ontario, all 

of the trees died over time due to a combination of 

defoliation and guano. Damage to vegetation can occur 

relatively quickly after cormorants move into an area. For 

instance, in the St. Lawrence estuary, cormorants on 

several islands caused irreversible damage to trees in less 

than 3 years. After cormorants started nesting on Young 

Island at Lake Champlain in 1982, all but one nesting tree 

was killed by 1996. 

In some cases, cormorant colonies have significantly 

affected rare plant communities. For example, the islands 

in western Lake Erie are home to rare Carolinian 

woodlands with stands of Kentucky coffeetree. Large 

cormorant colonies there could threaten the continued 

existence of these plants. 

In the Green Bay area of Wisconsin, vegetation on several 

islands has been impacted by cormorants. Habitat 

changes have allowed other ground nesting species to 

occupy these islands, which can perpetuate damage even 

in the absence of cormorants. In the southeast on Lake 

Guntersville, Alabama, cormorant breeding colonies have 

also caused nearly complete loss of trees on once forested 

islands (Figure 2). 

The interactions between colonial water-birds and 

vegetation are natural occurrences that have taken place 

throughout history. Succession of plant and avian 

communities caused by these changes may not be 

negative from a conservation or management perspective. 

However, in human-altered ecosystems where alternative 

habitat is limited or unavailable, cormorants can affect the 

persistence of plant communities and other wildlife 

species that rely on these habitats. 

The strong odor of droppings near roosts and nesting 

areas, along with the loss of vegetation, may reduce 

nearby property values. Tourists attracted to the natural 

beauty of waterfront areas may view the areas as 

unattractive once cormorants take up residence. On a local 

scale, decreasing property values and reduced tourism and 

recreation may cause economic losses for area residents 

and businesses that rely on income from tourism. 

Human Health and Safety

Humans should avoid direct contact with excrement from 

wildlife, including droppings from cormorants. Cormorants 

can present a bird-strike hazard when their populations 

and nesting or foraging habitats occur in or near the flight 

Figure 2. Impacts of breeding double-crested cormorants on trees in 

Guntersville Lake, Alabama

Page 2 WDM Technical Series─Double-crested Cormorants
paths of planes. Although only 4 to 5 incidents with cormorants are reported per year in the Federal Aviation Administration wildlife-aircraft strike database, damage can be 

severe due to the cormorant’s large size and weight. 

Newcastle disease, a viral disease that can affect all bird 

species, was first recognized in double-crested cormorants 

in the St. Lawrence River Estuary, Quebec, in 1975. In 

1992, double-crested cormorants in 7 states died from the 

disease. This widespread epidemic affected cormorants 

from the interior population, causing juvenile mortality 

rates ranging from 10 to 90%. By the late 1990s, outbreaks had occurred in cormorant populations across 

North America. The frequency of outbreaks in cormorants 

seems to be increasing since 2003, although the cause is 

unknown. Symptoms include lethargy, twisting of the head 

and neck, lack of muscular coordination, tremors, incomplete paralysis, and weakness of the legs and wings. 

Possible transmission of Newcastle disease from freeranging, wild birds to poultry is a concern, although there 

have been only 2 or 3 reported incidents worldwide possibly linking double-crested cormorants and other related 

waterbird species to outbreaks in domestic poultry. No 

extensive mortality to Newcastle diseases has been reported in other wild birds that share habitat with infected double-crested cormorants. Infections identical to those found 

in cormorants, however, have been isolated from American 

white pelicans and ring-billed gulls. 

People also can contract Newcastle disease. Symptoms, 

including conjunctivitis, fever, headache, and malaise usually are mild and last 3 to 4 days. Newcastle disease is 

transmitted through bird guano, or by humans who have 

been in contact with infected birds. Therefore, people working with double-crested cormorants should take measures 

to prevent infecting other birds, wild or domestic. After handling cormorants, disinfect hands, footwear, and equipment, and wash all clothing. 

Nuisance Problems 

Cormorants may foul docks and navigation devices with 

feces while roosting or drying their wings when foraging. 

Damage to Fisheries 

Flocks of foraging cormorants are easy to identify and often are reported by local anglers. Damage typically is reported by anglers as reduced catch or by aquaculture producers as reduced harvest. In recreational fisheries, state 

agencies also may report declines in sport fish numbers 

during monitoring efforts. 

Cormorant diet studies often have concluded that cormorants have little impact on recreational or commercial fishing because these fish make up a small percentage of cormorant diets. Diet studies by themselves, however, typically do not measure impacts to fish populations. Many diet 

studies are conducted during periods when sportfish are 

not normally consumed by cormorants and after sportfish 

populations have declined, which can contribute to low 

estimated consumption rates. Cormorants also are opportunistic predators whose diet varies considerably with local 

prey availability. For example, investigators found that the 

percent of sport and commercially significant species in 

the diet of double-crested cormorants feeding at a Wyoming river varied from less than 1% to 93%. On Lake 

Champlain in Vermont and New York, diet studies conducted before and after establishment of alewives showed a 

shift in diet from primarily yellow perch to alewife. At Rice 

Island in the Columbia River estuary, salmonids, some of 

which are federally-listed as threatened or endangered, 

were the most important prey of double-crested cormorants. 

Cormorants typically prey on specific size and age classes 

of sportfish. When they consume a large percentage of 

specific age-class fish, they may limit recruitment, even 

when consumption of sportfish is a relatively small percentage of total diet. This is particularly important if sportfish 

populations are low. In addition to rigorous diet studies, it 

is important to have information on the number of cormorants foraging, fish abundance, and age-specific fish mortality to fully understand the impacts of cormorants and 

effects of management if implemented. For example, in the 

Eastern Basin of Lake Ontario, 

Damage Identification

U.S. Department of Agriculture Page 3
researchers found a 36% reduction in 3- to 5-year old 

smallmouth bass resulted in an estimated 78% decline in 

recruitment to fishable stock from 1976 to 1998. In 

Brevoort Lake, Michigan, cormorant consumption of 

walleye, although less than 6% of the total diet, 

represented 55% of a year-1 walleye age class. Successive 

years of cormorant predation on a small number of age 

cohorts potentially can cause recruitment bottlenecks of 

harvestable fish age and size categories. 

Researchers have studied the walleye population, 

recreational fishery, and cormorant diet at Oneida Lake, 

New York, for decades. Based on over 40 years of fish 

population data, they concluded that cormorant predation 

likely was a significant source of sub-adult walleye 

mortality that negatively affected recruitment to the fishery. 

In recent years, several large studies of fishery-cormorant 

interactions have been conducted. In the eastern basin of 

Lake Ontario, declines in 2 important recreational fish 

species, smallmouth bass and yellow perch, coincided with 

increases in cormorants. A program to manage cormorants 

was implemented in 1999 that included egg-oiling, nest 

destruction, culling of breeding adults, and prevention of 

new colonies. These efforts resulted in a 50% decline in 

nesting numbers and a large reduction in numbers of fish 

fed to chicks. Smallmouth bass and yellow perch 

populations have remained consistently above low levels 

observed during peak cormorant nesting years. Cormorant 

management likely contributed to increased smallmouth 

bass and yellow perch abundance, but fish populations 

also may have been influenced by other contributing 

factors such as a recent increase in invasive round goby in 

the cormorant diet. In the Les Cheneaux Islands area of 

Michigan, a similar cormorant management effort using 

egg-oiling to limit reproduction and lethal control of adults 

on breeding colonies was implemented to improve the 

yellow perch fishery. Monitoring indicated that the yellow 

perch population improved to historical levels, an 

improvement that has been sustained for more than 5 

years. In Brevoort Lake, Michigan, a program of nonlethal 

harassment supplemented by limited lethal take of spring 

migrating cormorants to limit foraging on spawning walleye 

resulted in increased walleye survival and abundance. The 

above cases independently provide evidence that 

cormorants were impacting local fisheries and that 

management can improve fish stocks. The strength of 

evidence varies for each location, however, and in most 

cases results are confounded by other factors

The above management outcomes reflect situations in 

which long-term fishery data indicated cormorant predation 

was an issue; expertise and institutional commitment also 

supported multi-year management, research, and 

monitoring programs. Impacts of cormorants on fisheries 

typically are highly variable due to site-specific conditions. 

Aquatic systems are extremely complex, and the impacts of 

any single predator species are difficult to demonstrate 

with a high degree of certainty. 

In addition, cormorants and other birds can serve as 

potential vectors of diseases in fish. For example, 

cormorants likely are involved in the transmission of 

whirling disease in trout, but their role in the spread of 

disease is not understood.

A key to damage prevention is the integration of multiple 

methods that are complementary; a single technique used 

in isolation seldom is successful. Habitat management is 

the foundation of integrated wildlife management because 

it provides long-term protection and enhances the 

effectiveness of other control techniques, such as 

frightening devices. 

It is important to monitor the situation and apply control 

methods before or as soon as damage begins and only if 

damage is likely to be substantial. Money often is wasted 

when control techniques are implemented after substantial 

damage has been inflicted or the overall damage inflicted 

is minor and the cost of control exceeds the losses. 

Habitat Modification

Nest trees can be removed or destroyed with the hope that 

adult birds will either leave the area or fail to rebuild and re

-nest successfully that season. Removal of nest trees may 

Page 4 WDM Technical Series─Double-crested Cormorants

Management Methods
discourage cormorants from nesting in new areas, especially early in the nesting season. Removal of trees may not 

be a viable option where aesthetic or habitat impacts are a 

concern.

Fisheries Management

Hatchery-raised fish are particularly vulnerable when large 

numbers are released in a lake at once, or when spawning 

behavior or natural movements, such as runs of salmon 

smolts, concentrate fish in small areas. Release fish at 

night so they have time to disperse before cormorants 

begin feeding in the morning. In lakes, release fish in deep 

water, rather than from shore to reduce predation. In 

streams, stock fish early in the season before cormorants 

return from their wintering grounds. Fish also are vulnerable to cormorants when harvest methods congregate them 

in enclosed areas that cormorants can access. Use exclusion and frightening devices to reduce predation when 

stocking or harvesting fish. 

Exclusion

Physical barriers such as netting or grid wire systems can 

prevent cormorants from preying on fish in hatcheries or 

aquaculture ponds (Figure 3). Nets are effective when their 

edges extend to the ground surrounding the pond to prevent cormorants from walking under the netting and into 

the water. While physical barriers can be effective, they 

can be impractical and cost may be prohibitive for large 

ponds. In some instances, space may be limited for net 

supporting structures, and netting may interfere with machinery needed for daily operations. 

Overhead-wire systems make it difficult for cormorants to 

land on and take off from ponds. Although these systems 

are effective at preventing large flocks from landing, individual birds often learn to fly between the lines, or land on 

levies and walk into the pond despite the wires. Wire systems also can protect nesting colonies of other waterbirds. 

Along with gulls, cormorants can out-compete common 

terns for favored nesting islands. 

Wires suspended above nesting colonies of terns can enhance success and productivity by discouraging larger 

birds from nesting. This method effectively reserves nesting space for common terns until they are able to establish 

and defend a colony. Wires may reduce access to people 

and present hazards to non-target species such as swallows, osprey and bald eagles.

Ropes with plastic floats, sometimes called bird balls, are a 

less expensive and less labor-intensive alternative to wire 

systems. Floating ropes can be strung parallel to each other about 50 to 55 feet apart. The success of both wire systems and floating ropes depends on the availability of alternative foraging areas nearby. Birds that are able to find 

other food sources easily are more likely to be deterred. 

Changes in aquaculture practices may reduce depredation 

by cormorants and other fish eating birds. For example, in 

split-pond production systems (Figure 4), production of fish 

occurs in a much smaller area of the pond, making harassment of birds more effective and the use of physical barriers feasible. 

Frightening Devices

Harassment, or scare tactics, applied in an integrated and 

consistent fashion can discourage cormorants from using 

specific sites. Birds can be hazed at fish hatcheries and 

aquaculture facilities, as well as roosting and nesting sites 

on larger bodies of water. Harassment is most effective 

when the birds are not nesting or before birds have become habituated to a location. Cormorants learn quickly, 

U.S. Department of Agriculture Page 5

Figure 3. Overhead wires can be useful in protecting hatcheries from bird 

predation.
so frightening devices often do not deter the birds for long. 

For best results, use a variety of techniques and change 

the location and combination of devices frequently. 

Auditory 

Devices that make noise, including pyrotechnics such as 

shell crackers, screamers, whistling or exploding 

projectiles, bird bangers, propane cannons, and live 

ammunition, have been used to disperse cormorants with 

varying success. Live ammunition, while technically not a 

pyrotechnic, often is the least expensive and most readily 

available form of frightening device. Other methods may be 

more effective, but take care to avoid injuring or killing 

cormorants and other protected species. 

Hand-held lasers have been used successfully to disperse 

roosting cormorants and are most effective in low light 

conditions (twilight, nighttime, overcast skies). In addition, 

lasers are silent and can be used to move cormorants with 

minimal disturbance to non-target species. The regular 

presence of humans may frighten cormorants from smaller 

aquaculture or hatchery facilities, as well as from roosting 

sites and potential colonies. Encourage frequent human 

activity near valuable fish stocks to reduce depredation on 

fish. 

Visual

Visual harassment techniques (e.g. scarecrows, human 

effigies, and balloons) also have been tried with varying 

degrees of success. Mylar® tape (Figure 5) suspended on 

stakes near roosting and loafing sites has been effective in 

reducing cormorant use of areas. In addition, boats can be 

used to chase cormorants and successfully disperse roosts 

and flocks from ponds and larger bodies of water. 

Use of limited lethal control with harassment techniques 

may improve the effectiveness of harassment and is 

sometimes necessary to prevent acclimation to non-lethal 

methods.

Further effort in evaluation of novel non-lethal methods is 

being pursued. Researchers in Canada used a tethered 

raptor with some success to disperse nesting cormorants 

from a colony site. Drones are being investigated for their 

potential use in dispersing nesting cormorants from 

bridges, and to harass birds on ponds. 

Page 6 WDM Technical Series─Double-crested Cormorants

Figure 4. Aquaculture practices ,such as split pond catfish aquaculture 

designs, may reduce bird depredation on fish stocks.

Figure 5. Irri-TapeTM is Mylar-style tape used to frighten cormorants.
Repellents

None are registered.

Nest Removal and Treatment

Nests can be removed or destroyed to limit reproduction 

and disperse nesting birds. Nest destruction is relatively 

labor-intensive, although it can be practical on smaller colony sites. It requires more effort in colonies that are already established. High-pressure water sprays have been 

used to destroy cormorant nests in trees. Nest removal 

may be useful for discouraging cormorants from nesting in 

new areas, especially if nests are destroyed early in the 

nesting season. To be effective, control must be repeated 

throughout the nesting season, and likely on an annual 

basis. Nest removal may shift cormorants to other locations where they may cause continued conflicts.

Egg addling can be used to prevent or reduce population 

growth, and may be useful for eliminating colonies at specific locations, especially if combined with other harassment or population reduction methods. Eggs can be oiled 

(Figure 6) by spraying with food-grade corn oil to prevent 

the exchange of gases through the shell, causing asphyxiation of the embryo. Eggs also can be addled by vigorously 

shaking or puncturing them with a sharp small rod. The 

benefit of egg addling over destroying eggs is that cormorants will continue to incubate the eggs and are less likely 

to attempt to re-nest. Management strategies that include 

egg-oiling are best suited to situations where the presence 

of cormorants can be tolerated, and rapid population reduction is not the goal. Cormorants often re-nest, so some 

reproduction may still occur if persistent effort is not applied. In some states, a pesticide applicators license may 

be required for oiling eggs. 

Any technique that involves egg or nest destruction, or removal of cormorants likely will require federal and state 

permits or come under the authority of federal Aquaculture 

or Public Resource Depredation Orders.

Fertility Control

Currently no methods of surgical or chemical sterilization 

or immuno-contraception are available or practical for controlling cormorants. 

Toxicants

None are registered.

Trapping

Net Traps

Spring-loaded net traps (clap net traps) can be used to 

capture nesting colonial waterbirds. Place dummy eggs in a 

nest and set the trap so that it closes over a bird that 

comes to the nest. Monitor the nest from a nearby blind so 

the trapped bird can be removed from the trap quickly to 

prevent injury. After the bird is caught and euthanized or 

released, put the actual eggs back in the nest. Other lessused capture techniques for cormorants at their nests include swim-in traps, rocket and cannon nets, and net 

launchers. 

Foot-hold Traps

Place modified foot-hold traps at nests to capture adult 

birds during the breeding season in April and early May. 

U.S. Department of Agriculture Page 7

Figure 6. Spraying oil on eggs in double-crested cormorant nests. The typical 

3-person team has a backpack sprayer for food grade corn-oil, a person 

marking each nest with paint, and a data recorder.
Use a No. 3, padded-jaw, foot-hold traps that has been 

modified by replacing factory coil springs with weaker No. 

1.5 trap springs (Figure 7). Replace the trap chain with 

aircraft cable and a shock cord to minimize injury to 

trapped birds. Place dummy eggs in the nest during 

trapping (Figure 8). After the bird is caught and euthanized 

or released, put the actual eggs put back in the nest. 

Spotlights and Long-handled Nets

At night, cormorants can be disoriented by shining a 

spotlight on them and captured with a long-handled net on 

foot or by boat. This method works best on dark nights with 

low ambient light.

Shooting

Shooting allows for relatively rapid reduction in cormorant 

numbers. Shooting can be most effective on breeding 

colonies, where large numbers of birds congregate each 

day. Open-water shooting and removal at night roosts also 

can be used to protect specific sites. Cormorants respond 

well to both floating and silhouette decoys, which can 

make shooting more effective and reduce non-target take 

(Figure 9). 

Use a 12-gauge shotgun with No. 4 or 6 non-toxic shot size. 

Qualified agency personnel may also use suppressed 0.22-

or 0.177-caliber rifles on nesting colonies. Shooters should 

be knowledgeable in waterbird identification to prevent 

killing non-target species. Shooting adult cormorants not 

only removes birds, but also harasses the remaining birds. 

Shooting can be combined with pyrotechnics to enhance 

the effectiveness of non-lethal control options. Remove 

carcasses by hand and dispose of them using approved 

methods.

Handling

Relocation

Capture and relocation is not practical or effective, and 

thus is not recommended.

Translocation

Capture and translocation usually is not practical for 

cormorant management. Cormorants often move to 

different roost or nesting locations due to management 

activities such as hazing. While translocation from, for 

example, a hazed site is desirable, translocation to other 

sites can have an unpredictable outcome (i.e. positive, 

negative, or neutral).

Page 8 WDM Technical Series─Double-crested Cormorants

Figure 7. No. 3 padded-jaw foothold trap. All 4 springs should be removed 

and replaced with 2 springs suitable for a No. 1.5 paddle-jaw foothold.

Figure 8. No. 1.5 foothold trap in place over dummy eggs in a cormorant 

nest.
Euthanasia

Shooting is the most common method of euthanasia for 

double-crested cormorants. If a bird requires euthanasia 

while in hand, cervical dislocation is the most practical 

technique.

Disposal

Check your local and state regulations regarding carcass 

disposal. Recovered banded cormorants should be reported by calling 1-800-327-BAND. 

Cormorants may be managed whenever their damage justifies the granting of the permits necessary to control them. 

Adult cormorants eat approximately 19 ounces of food per 

day, so local impacts of large flocks on fisheries can be 

substantial. Although cormorants frequently are blamed for 

reductions in fish harvests, this is not always substantiated. Sometimes other factors, such as pollution, invasive 

species, and habitat loss may be the primary factor or contributing factors in the decline of fisheries. 

Identification

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 double-crested cormorant 

(Phalacrocorax auritus; Figure 1), great cormorant 

(Phalacrocorax carbo), neotropic cormorant (Phalacrocorax 

brasilianus), red-faced cormorant (Phalacrocorax urile), 

pelagic cormorant (Phalacrocorax pelagicus), and Brandt’s 

cormorant (Phalacrocorax penicillatus). This chapter will 

focus on the double-crested cormorant, which is the most 

numerous and widely dispersed of the species. 

Physical Description

The double-crested cormorant (Figure 1) is a long-lived, 

colonial-nesting waterbird 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. Some 1- to 2-year-old juvenile cormorants have grey or tan plumage on their neck and 

breast. 

Double-crested cormorants are 29 to 36 inches long with a 

wingspan of 45 to 52 inches. They and weigh about 4 to 6 

pounds. On average, double-crested cormorants live about 

6 years, but a few over 22 years have been reported.

Range

The double-crested cormorant is found in association with 

water bodies across the continental U.S. and along the 

southern coast of Alaska (Figure 10). 

U.S. Department of Agriculture Page 9

Figure 9. Floating and silhouette decoys used in double-crested cormorant 

control. 

Economics

Species Overview
The breeding range of the cormorant is divided into 5 

geographic areas: Alaska, the Pacific coast, southern U.S., 

interior U.S. and Canada, and northeast Atlantic coast. A 

small number of double-crested cormorants breed in the 

southeastern U.S. Populations in the interior U.S. and 

Canada, northeast Atlantic coast, and southern U.S. have 

been increasing and expanding their range since 1980. 

Tracks and Sign

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, guano deposits, and their coarsely constructed 

stick nests in trees or on the ground. 

Voice and Sounds

Cormorants usually are silent, but make hoarse, grunting, 

and guttural calls at breeding colonies and roost sites.

Reproduction

Cormorants are monogamous and breed in colonies ranging from several to over 10,000 pairs (Figure 11). Most 

double-crested cormorants return to the same location to 

breed year after year. Young cormorants often return to the 

colony where they hatched or to nearby areas to breed. 

Most cormorants are sexually mature by their third year, 

but a small number breed a year sooner. 

Normally cormorants have only 1 clutch per year, although 

they readily re-lay if eggs are taken by predators or destroyed. Clutch sizes range from 1 to7, with 4 eggs being 

most common. Both sexes incubate the eggs and incubation lasts 25 to 28 days. Embryos are tolerant of cold but 

not of heat. Hatchlings are altricial and weak, but growth is 

rapid, with chicks reaching about 90% of fledgling mass in 

24 days. Young birds can walk by 3 weeks and begin to fly 

at 6 to 8 weeks. Fledglings are completely independent 

about 10 weeks after hatching.

Nesting Cover

Males typically show up first, unpaired, on the breeding 

grounds and establish territories. Pairs form and begin 

constructing elevated platform nests composed of twigs, 

branches, and other plant materials in April to May. These 

nests often reach a height of 12 to 20 inches and may be 

re-used in subsequent years.

Page 10 WDM Technical Series─Double-crested Cormorants

Figure 10. Range of double-crested cormorant.

Figure 11. After a dramatic decline from the 1950s to 1970s, numbers of 

double-crested cormorants and breeding colonies have increased.
Cormorants typically use islands from 1 to 15 acres, with 

larger colonies often at more remote locations. Cormorants 

nest in trees, on cliffs, or on the ground (Figure 12). After 

years of repeated nesting in the same location, their guano 

often kills trees and other vegetation.

Cormorants are attracted to nesting sites of other colonial 

waterbirds and may compete with gulls, terns, egrets, herons, and some waterfowl (Figure 13). Cormorant guano 

deposited under nest trees can kill understory vegetation 

important for nesting black-crowned night herons and other tree-nesting species. At West Sister Island National Wildlife Refuge in Lake Erie, which supports one of the largest 

great blue heron colonies in the Great Lakes, heron numbers have declined annually since the double-crested cormorant arrived in 1992, presumably due to a combination 

of nest site competition, loss of nesting sites, and increased in human activity. 

Mortality

Double-crested cormorants commonly live more than 8 

years and occasionally 22 years or more in the wild. Estimated first-year mortality is over 50%, but survival greatly 

increases to over 80% annually for older birds. Eggs and 

chicks are taken by a variety of predators, particularly gulls 

and crows. Disturbance to colonies can cause extensive 

chick mortality due to predation and exposure. Adults have 

few predators, with the exception of eagles. Humans also 

affect cormorants and a substantial number are killed by 

entanglement in fishing gear. 

Population Status

In 2005, the continental population of cormorants was 

estimated between 1,080,800 and 2,163,600, which is 

similar to the estimates of 1 to 2 million individuals in the 

1990s. A dramatic population decline occurred between 

the 1950s and 1970s, caused by human persecution and 

chemical contamination from DDT. Cormorant numbers 

began to rebound in the mid-70s after 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 (e.g. alewife in 

the Great Lakes, stocked lakes, and catfish aquaculture in 

U.S. Department of Agriculture Page 11

Figure 12. Double-crested cormorants nesting on a cliff.

Figure 13. Double-crested cormorants competing with a herring gull for its 

nest site.
the Southeast), and cormorants were given protection by 

both federal and state laws. 

The interior meta-population generally is considered the 

largest, with close to half a million individuals. In the Great 

Lakes region, the number of cormorants increased an 

average of 29% per year from 1970 to 1991, after which 

population growth slowed. The Great Lakes metapopulation currently is stable or declining and may have 

reached carrying capacity in the North Channel of Lake 

Huron and other areas. The U.S. Fish and Wildlife Service 

(USFWS) reported that this decline was more pronounced 

in the US Great Lakes, where more management occurs, 

relative to the Canadian Great Lakes. 

Habitat

During the breeding season, double-crested cormorants 

inhabit lakes, ponds, slow-moving rivers, lagoons, 

estuaries, and open coastlines. They need suitable nesting 

sites with feeding areas nearby. Cormorants may nest on 

the ground, on steep cliffs, or on rocky or sandy islands, 

but they prefer to nest in trees. Nesting trees and 

structures usually are located near water, on islands, in 

swamps, or along tree-lined lakes. Cormorants typically 

choose live trees for nesting, although the trees often die 

within 3 to 10 years because of the significant 

accumulation of guano deposited on and beneath them. 

Outside of the breeding season, cormorants use a variety 

of habitats including marine islands and coastal bays. 

Cormorants establish nighttime roosts and daytime resting 

or loafing areas on sandbars, rocky shoals, cliffs, offshore 

rocks, utility poles, fishing piers, wires, channel markers, 

pilings, and trees near their fishing grounds. 

Behavior

Cormorants are expert divers, with webbed feet, 

streamlined bodies, and feathers that hold water and 

reduce buoyancy. They typically dive 8 to 25 feet, although 

depths of up to 85 feet have been recorded. After feeding, 

cormorants characteristically dry their feathers by perching 

with their wings outstretched (Figure 14). 

Double-crested cormorants of the Atlantic coast and interior populations are seasonal migrants. They leave the 

Northeast in September and migrate south along coastlines and river valleys. The 2 primary migration routes are 

down the Atlantic coast and through the Mississippi and 

Missouri River Valleys to the Gulf Coast. Cormorants return 

to their northern breeding grounds in late March or April. 

Home ranges of cormorants are highly variable and can be 

very large. Breeding season home ranges of cormorants 

marked with satellite transmitters ranged from 7 to over 

11,583 square miles. Winter home ranges show similarly 

large variation in size, ranging from 31 to 6,753 square 

miles. 

Food Habits

Double-crested cormorants feed almost exclusively on fish 

(Figure 15). They typically prey on small (less than 6 to 8 

inches), bottom-dwelling, or schooling “forage” fish, especially those that are most abundant and easiest to catch. 

This includes fish such as alewife, gizzard shad, yellow 

perch, sculpins, and sticklebacks. 

Diets of cormorants vary considerably from site to site and 

throughout the year. Their ability to catch fish depends on 

several factors, such as distribution, relative abundance, 

behavior, and habitat. Their diet often reflects the number 

and type of fish present in a given area at a given time.

Page 12 WDM Technical Series─Double-crested Cormorants

Figure 14. Double-crested cormorants perch on trees, rocks, buoys, and 

other objects that overhang or project from water.
Typically, cormorants feed during the day in water less than 

25 feet, within a few miles of the shore and their breeding 

colony. To capture fish, cormorants dive below the surface 

and pursue prey underwater. Dives may last from 17 to 34 

seconds or more. The birds sometimes swim with their 

heads submerged, searching for prey. They grasp prey in 

their bills and sometimes swallow fish underwater. Cormorants swallow large fish or those that are difficult to handle 

(e.g., eels or spiny fish), at the surface. At times, they throw 

their prey into the air, catch it, and swallow it head first. 

Cormorants typically forage individually, but may gather 

into feeding flocks of hundreds of birds, especially when 

preying on small schooling fish. 

Adult cormorants feed regurgitated food to their nestlings. 

To feed very young chicks, an adult will arch its neck, take 

the head of the chick into its mouth, and regurgitate a semi

-liquid food. Older nestlings will thrust their heads into the 

adult’s throat and remove whole fish regurgitated into the 

neck pouch. 

The U.S. Fish and Wildlife Service (USFWS) has the primary 

responsibility and authority for managing migratory bird 

populations in the U.S. This authority was established by 

the Migratory Bird Treaty Act (MBTA) of 1918, a treaty between the U.S. 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 U.S. Convention with Mexico was amended, 

and the double-crested cormorant was added to the list of 

migratory birds and given protection in the U.S .under the 

MBTA. Under this protection, cormorants cannot be captured or shot, and their nests and eggs cannot be disturbed unless a permit is obtained from the USFWS. 

U.S. Department of Agriculture Page 13

Figure 15. Double-crested cormorants feed on a variety of fish species.

Legal Status

Depredation permits to take cormorants have been issued 

by USFWS since 1986, primarily to federal, state, and tribal agencies and aquaculture producers, and may allow for 

the taking of adults, eggs, young, or active nests. 

In March 1998, the USFWS issued an Aquaculture Depredation Order (AQDO), allowing people engaged in commercial aquaculture to shoot cormorants without a federal 

permit at freshwater aquaculture facilities, or stateoperated hatcheries in Minnesota and 12 southeastern 

states. The AQDO allowed shooting of cormorants during 

daylight hours when necessary to protect aquaculture and 

hatchery stock if these actions were taken in conjunction 

with a non-lethal harassment program reviewed by the 

USDA-APHIS-Wildlife Services (WS). 

USDA-APHIS Wildlife Services

Although the USFWS has primary responsibility for managing cormorants, the USDA-APHIS-WS is the primary federal 

agency involved with on-the-ground management activities 

when cormorants cause damage. Wildlife Services helps 

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 addition, the USDA-APHIS-WS-National 

Wildlife Research Center is the primary federal program 
Page 14 WDM Technical Series─Double-crested Cormorants

involved with research on assessment and tools and 

techniques associated with reducing conflicts. 

State Wildlife Management Agencies

State wildlife agencies also are involved in management of 

double-crested cormorants. Double-crested cormorants are 

protected by migratory bird legislation in many states in 

addition to the MBTA. Cormorant control programs are 

being implemented in states, however, where birds are 

negatively affecting fish populations, vegetation, and other 

colonial water-birds. In New York and Vermont, programs 

are underway to prevent the spread of cormorants to other 

nesting islands in Lake Ontario, Oneida Lake, and Lake 

Champlain. 

In 2003, the USFWS, in cooperation with WS, finalized an 

Environmental Impact Statement (EIS) on double-crested 

cormorant management to address growing concerns from 

the public and natural resource management professionals 

about the population and range expansion of the doublecrested cormorant in the U.S. and their effects on local fish 

populations, other bird populations (including threatened 

and endangered species), vegetation and habitat, private 

property, and economic opportunities.

Increased Local Control

The USFWS issued new regulations in August 2003 that 

enhanced the flexibility of management agencies to deal 

with problems on a more local level, while ensuring the 

long-term sustainability of cormorant populations. The 

regulations included a new Public Resource Depredation 

Order (PRDO) that allows state fish and wildlife agencies, 

federally-recognized tribes, and WS to use lethal control 

measures to manage double-crested cormorants to 

address conflicts in 24 states, including: Alabama, 

Arkansas, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, 

Kentucky, Louisiana, Michigan, Minnesota, Mississippi, 

Missouri, New York, North Carolina, Ohio, Oklahoma, South 

Carolina, Tennessee, Texas, Vermont, West Virginia, and 

Wisconsin. 

According to the PRDO, lethal control, including shooting, 

egg-oiling or destruction, and nest destruction, can be 

carried out to protect public resources including fish, 

wildlife, plants, and other wild species on public lands and 

waters. With appropriate landowner permission, control 

activities also can take place on private lands where 

double-crested cormorants are causing harm to public 

resources. 
U.S. Department of Agriculture Page 15

Acknowledgements

Figure 1. Photo by USFWS

Figure 2. Photo by Jerry Feist, USDA-APHIS-WS 

Figure 3. Image by Prevention and Control of Wildlife Damage (PCWD) 

Figure 4. Image courtesy of Craig Tucker, USDA, Agriculture Research Service, Warmwater Aquaculture Research Unit, 

 Stoneville, MS

Figure 5. Photo by Bird-X, Inc. 

Figure 6. Photo courtesy of the New York Department of Environmental Conservation 

Figure 7. Photo by Stephen M. Vantassel

Figure 8. Photo by Elizabeth Craig

Figure 9. Photo by Tony Aderman, USDA-APHIS-WS 

Figure 10. Map from The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology 

Figure 11. Photo by Charles D. Lovell, USDA-APHIS-WS

Figure 12. Photo by Donna A. Dewhurst, USFWS 

Figure 13. Photo by Brian S. Dorr, USDA-APHIS-WS

Figure 14. Photo by Stan Tekiela

Figure 15 Photo by Brian S. Dorr, USDA-APHIS-WS

We thank Katie C. Hanson-Dorr and Fred C. Cunningham for their helpful comments and suggestions on an earlier version 

of this publication. 

Glossary

Recruitment: In the fish industry, reaching a certain size or 

reproductive stage. 

Salmonids: Fish in the family salmonidae, including salmon, trout, chars, graylings, and freshwater whitefishes. 

Split-pond system: A hybrid of recirculating and pond aquaculture production 

Key Words

Aquaculture, Co-nesting species, Cormorant, Doublecrested cormorant, Egg-oiling, Fisheries, Hatcheries, Nest 

destruction, Phalacrocorax auritus, Sportfish, Vegetation 

damage, Wildlife damage. 

Disclaimer

Wildlife can threaten the health and safety of you and others in the area. Use of damage prevention and control 

methods also may pose risks to humans, pets, livestock, 

other non-target animals, and the environment. Be aware 

of the risks and take steps to reduce or eliminate those 

risks. 

Some methods mentioned in this document may not be 

legal, permitted, or appropriate in your area. Read and follow all pesticide label recommendations and local requirements. Check with personnel from your state wildlife agency and local officials to determine if methods are acceptable and allowed. 

Mention of any products, trademarks, or brand names 

does not constitute endorsement, nor does omission constitute criticism. 
Page 16 WDM Technical Series─Double-crested Cormorants

Resources

Cornell University Cooperative Extension Wildlife Control Information Website. http://wildlifecontrol.info/ Accessed October 27, 2014. 

Dorr, Brian S., J. J. Hatch and D. V. Weseloh. 2014. Double-crested cormorant (Phalacrocorax auritus), The Birds of North 

America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. 

http://bna.birds.cornell.edu/bna/species/441/articles/introduction Accessed October 27, 2014. 

USDA-APHIS, Wildlife Services, National Wildlife Research Center. 

http://www.aphis.usda.gov/wps/portal/aphis/ourfocus/wildlifedamage?1dmy&urile=wcm%3apath%3a%2FAPHIS_Conte

nt_Library%2FSA_Our_Focus%2FSA_Wildlife_Damage%2FSA_Programs%2FSA_NWRC Accessed October 27, 2014. 

US National Cooperative Extension website (eXtension). http://extension.org Accessed October 27, 2014. 

The Internet Center for Wildlife Damage Management. http://ICWDM.org Accessed October 27, 2014.

National Wildlife Control Training Program. http://nwctp.com Accessed July 27, 2015. 
Appendix 

Page 17

 

 

Type of Control 

 

Available Management Options 

Exclusion  Monofilament or wire lines

 Netting

Fertility Control None available

Frightening Devices  Propane cannons

 Pyrotechnics

 Mylar® tape at nest sites

 Lasers

 Boats

 Effigies

Habitat Modification  Remove nest trees on islands

 Release fish at night or offshore

 Split-pond aquaculture systems

Nest Removal and 

Treatment

 Nest destruction

 High-pressure water spray to destroy nests

 Oiling or puncturing to destroy eggs

Repellents None registered

Shooting  12-gauge shotgun with No. 4 or 6 non-toxic shot

 Qualified agency personnel may use suppressed .22– or .177-caliber rifles on nesting colonies

Toxicants None registered

Trapping  Modified No. 3, padded-jaw foothold traps

 Clap net traps, swim-in traps

 Spotlight and net by hand at night from ground or boat

 Rocket and cannon nets, net guns, and net launchers

Damage Management Methods for Double-crested Cormorants