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Ardea albagreat egret

By Jessica Jones

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. (Connecticut Department of Environmental Protection, 2000)

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. (Connecticut Department of Environmental Protection, 2000)

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. (Gough, et al., 1998; Illinois Department of Natural Resources, 1998; Sheehey, 1998)

  • Range mass
    912 to 1140 g
    32.14 to 40.18 oz
  • Average length
    1 m
    3.28 ft
  • Average wingspan
    1.5 m
    4.92 ft

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. (Illinois Department of Natural Resources, 1998)

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. (Connecticut Department of Environmental Protection, 2000; Illinois Department of Natural Resources, 1998)

  • Breeding interval
    Great egrets breed once per year.
  • Breeding season
    Breeding season begins in mid-April.
  • Average eggs per season
    3-4
  • Average time to hatching
    23-24 days
  • Average fledging age
    2-3 weeks
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

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. (Connecticut Department of Environmental Protection, 2000; Illinois Department of Natural Resources, 1998)

  • 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). (Burger and Gochfeld, 1997)

  • Range lifespan
    Status: wild
    22.8 (high) years
  • Average lifespan
    Status: wild
    15 years
  • Average lifespan
    Status: captivity
    22 years
  • Average lifespan
    Status: wild
    274 months
    Bird Banding Laboratory

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. (Drummond, 2001; Illinois Department of Natural Resources, 1998; Kushlan, 1978)

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. (Chisholm, 2001; Oregon Zoo, 2002)

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. (Connecticut Department of Environmental Protection, 2000; Hill, 2001; Illinois Department of Natural Resources, 1998)

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. (Connecticut Department of Environmental Protection, 2000; Hill, 2001; Illinois Department of Natural Resources, 1998)

  • 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). (Connecticut Department of Environmental Protection, 2000; Illinois Department of Natural Resources, 1998)

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. (Connecticut Department of Environmental Protection, 2000)

  • 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. (Burger and Gochfeld, 1997; Connecticut Department of Environmental Protection, 2000)

Contributors

Alaine Camfield (editor), Animal Diversity Web.

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

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: 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: 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: 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.

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Classification

Classification

  • Kingdom Animalia animals
  • Phylum Chordata chordates
  • Subphylum Vertebrata vertebrates
  • Class Aves birds
  • Order Ciconiiformes storks and relatives
  • Family Ardeidae herons
  • Genus Ardea great herons
  • Species Ardea alba great egret