Michael D. Hoy 

District Supervisor

USDA-APHIS-Wildlife Services 

Almyra, Arkansas 

 

Human-Wildlife Conflicts

Landscapes

Herons and egrets commonly cause 

damage at aquaculture facilities and 

recreational fishing waters where fish are 

held at high densities. In one study, on 

average wading birds consumed from 4 to 

24 golden shiners per day at minnow 

production facilities in Arkansas. Great 

blue herons and great egrets commonly 

feed at catfish production facilities in 

Mississippi. The tendency for herons and 

egrets to congregate in large feeding 

flocks often leads to extensive loss of fish 

at aquaculture facilities.

Fish-eating birds also can have an impact 

on intensively managed sport fisheries. 

Damage occurs when herons and egrets 

feed on fish purchased and released for 

recreational sport fishing activities. Values 

of these fish can be quite high given the 

intensity of management activities and the 

direct relationship of fishery quality to 

property value. 

Livestock and Pets

Great blue herons are known to feed on 

fish in backyard water gardens. This can 

be a problem in urban areas as fish in 

these small ponds often are considered 

valuable pets.

Wildlife Damage Management 

Technical Series

U.S. Department of Agriculture

Animal & Plant Health Inspection Service

Wildlife Services

August 2017 Herons and Egrets

Figure 1. Great Blue Heron (Ardea herodias)

Quick Links

Human-Wildlife Conflicts 1

Damage Identification 2

Management Methods 2

Economics 4

Species Overview 5

Legal Status 9

Glossary & Key Words 10

Resources 11 

Appendix 12 
Human Health and Safety

Nesting colonies often cause problems in urban areas 

when urbanization spreads into lowland habitats where 

colonial nest sites have traditionally existed. Odor from 

deposited fecal material in these areas is a problem. 

Histoplasmosis is not commonly found in soils from heron/

egret rookeries, but proper conditions for this fungal 

disease exist in these areas. Rookeries near airports may 

pose a flight safety risk to aircraft.

Often, heron and egret damage initially is identified by the 

presence of birds feeding at the damage site. Further 

investigation will determine that fish are missing or 

damaged (Figure 2). Damage often includes puncture 

holes or slices on the back or sides of a fish. 

Occasionally, damage at aquaculture facilities is not 

realized until harvest when fish production falls short of 

expectations. This is often the case if ponds are not 

regularly frequented by humans or if birds are feeding at 

night.

Integration of multiple control methods is essential in 

developing a strategy to manage heron and egret damage. 

If implemented in a timely and persistent manner, all 

methods discussed below will provide effective control of 

wading bird damage. Reliance on one method rarely works 

to prevent or control extensive bird damage. When 

developing a control program, realize that every damage 

situation is unique. Incorporate the uniqueness of the 

situation into your control program and use as many 

control strategies as possible to develop your management 

strategy.

Habitat Modification

Small, shallow impoundments are attractive feeding sites 

for wading birds and should be avoided. Herons and egrets 

will rapidly congregate if fish are left in these conditions for 

extended periods. Shallow water conditions are often 

necessary to harvest commercial fish and cannot be 

avoided. If this occurs, be prepared to implement 

frightening devices to disperse the birds.

Diseased fish are highly vulnerable to heron and egret 

depredation. Maintain quality fish health standards to help 

minimize wading bird depredation.

Figure 2. Great blue heron damage to fish.

Page 2

Damage Identification

WDM Technical Series─Herons and Egrets

Management Methods

Figure 3. Herons and egrets prefer vegetated banks.
Herons and egrets prefer to feed along vegetated banks 

where they are concealed from their prey (Figure 3). Pond 

banks without vegetation are less attractive to birds and 

will decrease the efficiency of wading bird feeding. 

Urban rookeries can be prevented by adequately thinning 

nesting habitat. Since herons and egrets are protected 

under the Migratory Bird Treaty Act, habitat management 

in active rookeries is prohibited. All habitat modifications to 

prevent future rookeries must be performed during the 

nonbreeding season. In some situations, it is possible to 

get a Migratory Bird Depredation Permit from the U.S. Fish 

and Wildlife Service (USFWS) to allow habitat modifications 

during the breeding season. Contact your local USFWS 

office for further guidance.

Exclusion

Total exclusion is the complete enclosure of an area with 

netting or wire mesh caging to eliminate bird use (Figure 

4). Exclosures are the only way to completely restrict heron 

and egret access to ponds and raceways. It is effective, but 

due to cost and structural problems in spanning large 

distances, it is generally considered impractical to totally 

exclude birds at water holding structures larger than 5 

acres. In addition, exclosures are difficult to incorporate 

into a commercial aquaculture facility as they can interfere 

with fish management practices. 

Total exclosures are recommended for protection of fish in 

urban water gardens. The small ponds and high value fish 

make this control method cost effective. However, the 

exclusion system may be aesthetically unacceptable to the 

landowner.

Partial exclusion is the limited enclosure of an area with 

wire or string lines to discourage bird use (Figure 4). The 

lines are run laterally or set in a grid pattern across ponds 

or raceways to impede access by birds. Partial exclusion is 

usually less expensive than total exclosure, but will not 

eliminate heron and egret use of the site. As with total 

exclusion, overhead wire systems are impractical for large 

ponds due to the difficulty in spanning large distances. 

Overhead wire exclosures are easier to incorporate with 

fish management practices and are easier to maintain 

than complete enclosures. Overhead wire systems are 

considered cost effective for small ponds (less than 5 

acres). It is recommended that high-value fish subject to 

predation by herons and egrets be raised in small ponds 

with overhead wire systems.

All exclusion systems must be structurally sufficient to 

withstand the weight and impact of birds. Consider 

weather conditions; the infrastructure should be strong 

enough to support accumulations of ice and snow.

U.S. Department of Agriculture Page 3

Figure 4. A total exclosure eliminates access by birds completely (a), 

whereas overhead lines or wires provide only partial exclusion (b).

A

B
Perimeter fencing and wires have been used with limited 

success to exclude herons and egrets from ponds. Wading 

birds quickly acclimate to barriers and jump over wires to 

feed on fish. Electric perimeter wires also have proven to 

be ineffective and impractical for most situations.

Frightening Devices

Frightening devices are effective tools for dispersing large 

concentrations of herons and egrets from damage sites. 

Many visual and noise-making devices are commercially 

available for scaring birds, including gas-operated 

exploders, pyrotechnics, electronic noise makers, bird 

distress calls, effigies, eyespot balloons (Figure 5), 

reflective tape, and water spray devices. Methods for 

incorporating these devices into a bird scaring program are 

described in the Bird Dispersal Techniques publication of 

the Wildlife Damage Management Technical Series. As 

discussed previously, it is important to use a variety of 

frightening devices in a timely and persistent manner.

At large aquaculture facilities, the effectiveness of these 

devices is compromised over time as herons and egrets 

become habituated to the deterrents. At this point, 

frightening devices will simply push herons and egrets from 

one pond to another nearby pond where they will continue 

feeding. Lethal control may be necessary to enhance the 

overall effectiveness of a bird scaring program at these 

sites. See the Shooting section for more details.

At urban rookeries, frightening devices can be used to 

relocate birds prior to nesting. Once active nests are 

established, it is illegal to intentionally disperse birds from 

a nest site. Contact the USFWS for further clarification.

Repellents

None are registered.

Fertility Control

None are available.

Toxicants

None are registered.

Trapping

Allowed with permits, but typically ineffective at controlling 

damage.

Shooting

It is illegal to shoot herons and egrets without a permit 

from the USFWS. A permit can be obtained by commercial 

fish farms to augment their on-going nonlethal harassment 

programs. Contact USDA APHIS Wildlife Services or your 

state wildlife agency for more information.

Heron and egret damage is difficult to quantify. The relative 

abundance of fish among aquaculture ponds is highly 

variable. Therefore, it is difficult to assess the overall 

impact of bird depredation until harvest. 

Loss estimation requires knowledge of the number of birds 

present, feeding duration, number of fish taken, and the 

crop value. One study assessed esophageal and stomach 

contents of 4 species of herons in Arkansas and found 

losses of golden shiners ranged from $0.10 to $0.62 per 

feeding. Based on 2 feedings per day, a flock of 100 

wading birds present on a fish farm for a 3-month period 

Page 4 WDM Technical Series─Herons and Egrets

Figure 5. “Eye-spot” balloons may help protect small areas from heron and 

egret damage for a limited period of time.

Economics
resulted in losses from $1,800 to $11,160, depending on 

the species composition. 

Indirect economic impact can occur when herons carry 

unwanted fish and vegetation into the aquaculture facility. 

Cross contamination of fish from nearby ponds can lead to 

unwanted polyculture and decreased crop values. Birds 

also have been implicated in the spread of fish diseases 

between pond complexes. 

Identification

Herons and egrets are freshwater or coastal birds of the 

family Ardeidae. The most common species include:

 Great blue heron (Ardea herodias)

 Great egret (Casmerodius albus)

 Snowy egret (Egretta thula)

 Little blue heron (Egretta caerulea)

 Cattle egret (Bubulcus ibis)

 Green heron (Butorides virescens)

 Black-crowned night-heron (Nycticorax nycticorax)

 Yellow-crowned night-heron (Nycticorax violaceus)

Physical Description

Herons and egrets are medium to large sized birds with 

characteristic long legs, necks, and pointed bills. Legs are 

extended and heads retracted during flight. They are 

sexually monomorphic and typically colonial nesters. The 

great blue heron (Figure 1) is approximately 4 feet tall with 

blue-grey plumage and weighs between 5 and 6 pounds.

Great egrets (Figure 6) are slightly smaller than great blue 

herons and are white with black legs. 

Snowy egrets (Figure 7) are approximately 27 inches tall 

and are white with black bills and legs and characteristic 

yellow feet. 

Little blue herons (Figure 8) are similar in size to snowy 

egrets, but blue grey with a maroon neck. Immature little 

blue herons are dusky white with dull green legs. 

Cattle egrets (Figure 9) are slightly smaller than snowy 

egrets and are white with yellow bills and dark yellow or 

coral legs.

Green-backed herons (Figure 10) are approximately 28 

inches tall, with a blue-green back and chestnut neck. 

Night-herons are similar in size to snowy egrets but grey, 

short-legged and thick-billed. Black-crowned night-herons 

have a black back and neck (Figure 11). 

Yellow-crowned night-herons (Figure 12) are similar to 

black-crowned, but have a white cap and cheek patch.

U.S. Department of Agriculture Page 5

Figure 6. Great egret walking through water. Species Overview

Figure 7. Snowy egret with characteristic yellow feet.
Page 6 WDM Technical Series─Herons and Egrets

Figure 10. Green-backed heron. 

Figure 8. Little blue heron.

Figure 11. Black-crowned night heron in water. 

Figure 9. Cattle egret.

Figure 12. Yellow-crowned night heron showing white cheek patch and cap.
Range

The great blue heron can be found in wetland areas across 

most of the U.S. and lower Canada (Figure 13). The great 

egret occurs along coastal U.S. with many wintering areas 

in South and Central America (Figure 14). The cattle egret 

appeared in North America in the 1950s; by the 1990s, it 

had become common in many regions. For range 

information on other species, please see The Birds of 

North America Online.

Tracks and Sign

Herons and egrets are most frequently identified by 

sightings near water or concentrations at communal 

roosts. For sign associated with aquaculture damage, see 

section on Damage Identification.

Voice and Sounds 

Herons and egrets have distinctive vocalizations, but these 

generally are not beneficial for identification. The most 

common sounds associated with great blue herons are 

squeaking roh-roh-rohs when landing or a series of 

clucking go-go-gos building to a rapid frawnk squawk. 

Great egrets make dry, croaking sounds, nasal squeals and 

other harsh calls. For vocalizations of other species, please 

see The Birds of North America Online.

U.S. Department of Agriculture Page 7

Figure 13. Breeding, non-breeding, and year-round ranges of the Figure 14. Distribution of great egret.

great blue heron.
Reproduction

The size of the clutch, length of incubation, and age at 

which birds reach sexual maturity varies by species. Great 

blue herons breed from March to May in the northern part 

of their range. Females lay 3 to 6 eggs after mating. Those 

living farther north have the higher clutch sizes. Both sexes 

incubate the eggs, which hatch after 26 to 30 days. 

Parents feed the young by regurgitating food at the nest. 

The young fledge about 2 months after hatching and are 

sexually mature at about 22 months. Great egret females 

lay 3 to 4 eggs after mating. Both sexes incubate the eggs, 

which hatch in about 24 days. The young fledge about 2 to 

3 weeks after hatching and can reproduce after 2 years. 

For information on other species, please see The Birds of 

North America Online.

Mortality

Great blue herons commonly live more than 15 years and 

occasionally 24 years or more in the wild. More than half of 

the great blue herons born in any given year die before 

they are a year old. Great egrets have similar lifespans and 

mortality rates. For information on other species, please 

see The Birds of North America Online.

Population Status

The great blue heron and great egret suffered from heavy 

hunting pressure in the late 1800s and early 1900s for 

their breeding plumes. That, along with habitat loss due to 

drainage of wetlands, had a negative impact on their 

populations. According to the North American Breeding 

Bird Survey, populations of great egrets increased 

significantly from 1966 to 2010 in the U.S. The little blue 

heron, cattle egret, and green heron showed declines in 

population over the same years. For information on other 

species, please see The Birds of North America Online.

Habitat

Varies by species, but all are associated with wetlands 

throughout their life history. According to the Birds of North 

America online, the cattle egret’s preference for “lawns, 

fields, pastures and grazing animals is quite unlike other 

native North American herons and egrets, which generally 

feed in or along water and not in close association with 

livestock.”

Behavior

Foraging habits vary by species, but herons and egrets 

typically wade in shallow water in pursuit of prey. Feeding 

by hovering and diving by these species has been observed 

when fish are concentrated in deep, open water. Great 

blue herons are known to herd minnows toward shallows 

of aquaculture ponds to increase foraging efficiency.

Herons and egrets are diurnal sight feeders that return to 

roost at dusk. They will feed at night with favorable 

moonlight or when disturbed from feeding during the day. 

Night-herons are the exception, as they prefer to feed at 

night and roost during the day.

Herons and egrets are known to congregate in large flocks 

when fish are concentrated in shallow water.

Species in the Family Ardeidae are typically colonial 

nesters. Their rookeries are often found in densely 

vegetated, lowland habitats or wetland areas.

Page 8 WDM Technical Series─Herons and Egrets

Figure 15. Great blue heron eating a fish.
Food Habits

Herons and egrets discussed in this section are all 

piscivorous (Figure 15). They are opportunistic feeders, 

however, and will consume small amphibians, insects, and 

reptiles. Due to these food preferences, herons and egrets 

are attracted to shallow lakes and human-made 

impoundments. 

Native bird species are covered under the Migratory Bird 

Treaty Act (MBTA) and given federal protection. 

Depredation permits can be obtained through the U.S. Fish 

and Wildlife Service. In addition, individual states may 

require their own permits for legal take of these bird 

species.

U.S. Department of Agriculture Page 9

Legal Status
Page 10 WDM Technical Series─Herons and Egrets

Acknowledgements

Figure 1. Photo by Robert Burton, USFWS

Figure 2. Photo by USDA

Figure 3, 6 and 8. Photos by Steve Hillebrand, USFWS

Figure 4. Images from 1994 Prevention and Control of Wildlife Damage

Figure 5. Photo by John Humphreys, USDA-APHIS-WS

Figure 7. Photo by Jama Beasley, USFWS 

Figure 9 and 10. Photos by Lee Karney, USFWS

Figure 11. Photo by Erni, Shutterstock.com

Figure 12. Photo by Mark Musselman, National Audubon Society and USFWS

Figures 13 and 14. Maps from The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.

Figure 15. Photo by Don Mammoser, Shutterstock.com

Portions of Prevention and Control of Wildlife Damage, 1994, Bird Damage at Aquaculture Facilities by W. Paul Gorenzal, 

Fred S. Conte, and Terrell P. Salmon were used in development of this publication. Special thanks to Thurman Booth, Brian 

Dorr, Harris Glass, Kris Godwin and Michael Kearby for their critical review.

Key Words

Aquaculture, Ardea herodias, Casmerodius albus, Egret, 

Fish predation, Heron

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. 

Citation

Hoy, M.D. 2017. Herons and Egrets. Wildlife Damage 

Management Technical Series. USDA, APHIS, WS National 

Wildlife Research Center. Fort Collins, Colorado. 12p.

Glossary

Piscivore: An animal that feeds on fish. 

Polyculture: The simultaneous cultivation of several crops 

or kinds of animals. 

Rookery: A colony of breeding birds; the nesting place of 

birds. For herons, it may be called a heronry.

Sexual Monomorphism: The males and females of a 

species show no differences in coloration, size or body 

structure other than their genitalia. 
U.S. Department of Agriculture Page 11

Resources

Glahn, J.F., D.S. Reinhold, and P. Smith. 1999. Wading bird depredations on channel catfish (Ictalurus punctatus) in 

northwest Mississippi. J. World Aquaculture Soc. 30:107-114.

Hoy, M.D., J.W. Jones, and A.E. Bivings. 1989. Economic impact and control of wading birds at Arkansas minnow ponds. 

Eastern Wildl. Damage Control Conf. 4:109-112.

Hoy, M.D. 1994. Depredations by herons and egrets at bait fish farms in Arkansas. Aquaculture 20:52-56.

Krebs, J.R., and B. Partridge. 1973. Significance of head tilting in the great blue heron. Nature 242:533-535.

Kushlan, J.A. 1976. Wading bird predation in a seasonally fluctuating pond. Au. 93:464-476.

Kushlan, J.A. 1978. Feeding ecology of wading birds. Pages 249-297 in A. Sprunt, J.C. Ogden, and S. Winckler, eds. 

Wading birds. Rep. No.7. Natl. Audubon Soc., New York.

McCrimmon, Jr., Donald A., John C. Ogden and G. Thomas Bancroft. 2011. Great Egret (Ardea alba), The Birds of North 

America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; accessed Sept. 17, 2015 from the Birds of North 

America Online at: http://bna.birds.cornell.edu/bna/species/570

Telfair II, Raymond C. 2006. Cattle Egret (Bubulcus ibis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell 

Lab of Ornithology; accessed Sept. 17, 2015 from the Birds of North America Online at http://bna.birds.cornell.edu/

bna/species/113

Vennesland, Ross G. and Robert W. Butler. 2011. Great Blue Heron (Ardea herodias), The Birds of North America Online 

(A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; accessed Sept. 17, 2015 from the Birds of North America Online at 

http://bna.birds.cornell.edu/bna/species/025

Internet Center for Wildlife Damage Management (http://icwdm.org)

National Wildlife Control Training Program (http://wildlifecontroltraining.com)

The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology
Appendix 

Page 12

 

 

Type of Control 

 

Available Management Options 

Exclusion  Total exclosures are recommended for protection of fish in urban water gardens.

 Overhead wires are more practical for larger areas.

Fertility Control None available.

Frightening Devices  Propane cannons, pyrotechnics, and other noise making devices.

 Various visual devices effective on small ponds including flash tape, mylar balloons, scarecrows 

and effigies.

 Distress calls generally ineffective.

Habitat Modification  Maintain water depth, promote steep pond banks, and eliminate vegetation at waterline at 

aquaculture facilities.

 Thin vegetation at roost sites.

Repellents None registered.

Shooting Allowed with proper Federal and State permits.

Toxicants None registered.

Trapping Allowed with proper permits, but generally not effective for controlling damage.

Damage Management Methods for Herons and Egrets