Ardea alba

Geographic Range

Great egrets are found in the Nearctic as far south as Texas, the Gulf coast states, and Florida up the Atlantic coast to Maine and southern Canada, and west to the Great Lakes.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

The ideal location for great egrets is near any form of water. Streams, lakes, ponds, mud flats, saltwater and freshwater marshes are inhabited by this beautiful bird. Wooded swamps and wetlands are the preferred location for great egrets and other heron species.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal
• brackish water brackish water

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

• Other Habitat Features
• riparian riparian
• estuarine estuarine

Physical Description

Great egrets are less then 1 meter long from bill to tail, 1 meter tall, have a wingspan of 1.5 meters, and weigh about 912 to 1140 g. On average, males are larger than females. They are completely white with a long yellow bill and dark gray legs. During flight their neck is usually in an “S” shaped curve. They are very elegant birds with plumage resembling lace.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• ornamentation ornamentation

Development

Nestlings are virtually helpless and covered with a layer of long white down feathers and begin to fly at about 42 days after hatching (Illinois Department of Natural Resources [INHS] 1998).

Reproduction

Great egrets are seasonally monogamous animals. Male egrets are responsible for selecting a territory and performing a series of rituals in order to attract a female. Copulation occurs within the males’ territory.

• Mating System
• monogamous monogamous

Typically, great egret nests are built with other heron nests in a colony in wetlands and wooded swamps. Nests are a flimsy platform constructed of sticks, twigs, and stems built as high as possible. The eggs are a pale greenish blue, and are incubated by both the male and female for about 23 to 24 days. Nestlings usually fledge 2-3 weeks after hatching. With a clutch size of only 3-4 eggs, great egrets will lay replacement eggs if any of the first eggs are damaged. Great egrets are capable of reproducing after two years and raise one brood per year. The breeding season begins mid-April.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Both male and female great egrets participate in incubating and feeding the semi-altricial young. Nestlings are initially fed by regurgitation, followed by bill-grabbing, where the parent holds prey over the nestling to grab at as it eats.

• Parental Investment
• no parental involvement
• pre-fertilization
• pre-hatching/birth
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female

Lifespan/Longevity

Great egrets have a lifespan of about 15 years in the wild (22 in captivity).

Behavior

Great egrets are very territorial when it comes to courtship, nesting and feeding. They are diurnal feeders and at dusk they gather from surrounding areas to form communal roosts. Post-breeding dispersal is very common among great egrets. After the young hatch, they accompany the adults on long journeys. Many heron species rob other species in order to obtain more food. Great egrets steal a very high percentage of their food from other smaller herons. They also fight for food within their own brood. For many avian species food availability has an effect on aggression. However, it has been found that great egrets are highly aggressive in many situations even when food is not limited.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• territorial territorial
• colonial colonial

Home Range

There is no information available on the home range for this species at this time.

Communication and Perception

Great grets communicate through elaborate courtship rituals, and with vocalizations that are a harsh low “corr”. Much of the way these birds communicate is illustrated by their elaborate courtship dances, and territoriality. When defending their territory they may squawk harshly, leap at, or jab their beak at the intruder.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Frogs, snakes, crayfish, fish, mice, crickets, aquatic insects, grasshoppers, and many other insects constitute the typical diet of a great egret. Other large wading birds have similar feeding habits and compete with great egrets for food resources.

As opportunistic predators, great egrets usually feed on smaller aquatic and terrestrial insects and vertebrates and are considered to be heterotrophs. Wading slowly through the water, they are extremely successful at striking and catching fish or insects. Studies found that, standing still, great egrets were able to ingest more prey of intermediate size than if they moved around. This suggests that their goal is not to catch the largest quantity of food, but to catch high quality food.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• mammals
• amphibians
• reptiles
• fish
• insects
• aquatic crustaceans

Predation

Adult great egrets have no non-human predators and now have some legal protection against humans. However, eggs and nestlings are exposed to numerous predators including crows (family Corvidae ), vultures (family Cathartidae ), and raccoons ( Procyon lotor , which are the most threatening).

Ecosystem Roles

As predators great egrets affect the populations of their prey.

Economic Importance for Humans: Positive

Prior to the 20th century there was great demand for the lacey plumage of great egrets for women's hats and other fashionable garments.

• Positive Impacts
• body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse affects of great egrets on humans.

Conservation Status

Prior to the 20th century, the population of great egrets was nearly decimated by the demand for their lacey plumage for women’s hats and other fashionable garments. With great concern for the welfare of great egrets, legal restrictions were placed on the harvesting of this animal. Great egrets were placed under the protection of the Migratory Bird Treaty Act in 1918. By the mid 1900's populations of great egrets were steadily on the rise. Today, populations are doing well. However, there are still many human-induced threats to the survival of great egrets. Loss of habitat, water pollution, and various air pollutants all contribute to the dangers faced by great egrets. Hydrocarbons are especially problematic because they cause great egrets to lay thinner eggs that are more susceptible to cracking or damage before the young hatch. Mercury has been found at high levels in the feathers of numerous avian species including great egrets. The amount of mercury found depends on age, sex, geographic location, and mercury concentrations in the habitat around them including the air, soil and organisms they consume. These contaminations have also been found to negatively effect behavior, physiology, and reproduction.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Alaine Camfield (editor), Animal Diversity Web.

Jessica Jones (author), Western Maryland College, Randall L. Morrison (editor), Western Maryland College.

References

Burger, J., M. Gochfeld. 1997. Risk, mercury levels, and birds: relating adverse laboratory effects to field biomonitoring. Environmental Research , 75: 160-172.

Chisholm, D. 2001. Showy snowy and great egrets!. Photographic Society of America Journal , November 67: 32.

Connecticut Department of Environmental Protection, 2000. "Wildlife in Connecticut" (On-line). Accessed 11/20/2003 at http://dep.state.ct.us/burnatr/wildlife/factshts/gegret.htm .

Drummond, H. 2001. A revaluation of the role of food in broodmate aggression. Animal Behaviour , 61 61: 517-526.

Gough, G., J. Sauer, M. Iliff. 1998. "Patuxent Bird Identification Infocenter" (On-line). Accessed 11/20/2003 at http://www.mbr-pwrc.usgs.gov/Infocenter/infocenter.html .

Hill, K. 2001. "Smithsonian Marine Station at Fort Pierce" (On-line). Accessed 11/20/2003 at http://www.sms.si.edu/IRLSpec/Ardea_alba.htm .

Illinois Department of Natural Resources, 1998. "Illinois Natural History Survey" (On-line). Accessed 11/20/2003 at http://www.inhs.uiuc.edu/chf/pub/ifwis/birds/great-egret.html .

Kushlan, J. 1978. Nonrigorous foraging by robbing egrets. Ecology , 59, No. 4 59: 649-653.

Oregon Zoo, 2002. "Oregon Zoo Animals:Great Egret" (On-line). Accessed 11/20/2003 at http://www.zooregon.org/Cards/Cascades/great_egrets.htm .

Sheehey, A. 1998. "A Field Guide to the Birds of Kern County" (On-line). Accessed 11/20/2003 at http://www.natureali.com/GrEg.htm .