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Species in this Guide: 636
Plum Island Ecosystems LTER, Rowley, Massachusetts
Created by: Samuel Kelsey and Samantha Bond
Snowy Egret - Egretta Thula  Egretta thula         View on EOL
Overview

Taxon Biology

Smaller (20-27 inches) than North America’s other light-colored herons and egrets, the Snowy Egret is most easily identified by its black bill, black legs, yellow feet, and regal breeding plumes. Other field marks include an all-white body, short tail, and small yellow skin patch on the face. Male and female Snowy Egrets are similar to one another in all seasons. The Snowy Egret breeds along the east coast of the United States north to Maine and locally in the interior southeast and west. Coastal birds are non-migratory, while interior birds migrate to the Atlantic and Gulf coasts, the Pacific coast of California and in the interior from northern Mexico south to Panama. Other non-migratory populations occur along both coasts of Mexico and Central America as well as in the West Indies. Snowy Egrets live in and around small bodies of water. In summer, Snowy Egrets nest in colonies, called ‘rookeries,’ in trees surrounding lakes and ponds. This species utilizes similar habitats during the winter. Snowy Egrets mainly eat fish, but may also take crustaceans and small vertebrates (such as frogs, lizards, and mice) when the opportunity arises. Snowy Egrets may be best observed wading in shallow water, where they may be seen plunging their bills into the water to catch fish. It is also possible to see Snowy Egrets at their rookeries, especially when they return to roost at sunset, or while flying with their feet extended and their necks pulled in. Snowy Egrets are primarily active during the day.

Threat Status: Least concern
Publisher: Smithsonian Institution, Contributor: Smithsonian Institution, Creator: Reid Rumelt, Author: Reid Rumelt, Provider: DC Birds  Source: Unknown   CC License: by-nc-sa

Distribution

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: northern California, southern Idaho, Kansas, lower Mississippi Valley, and Gulf and Atlantic coasts north to Maine, south through Mexico and the Antilles to South America (to southern Chile and central Argentina). See Spendelow and Patton (1988) for information on the distribution and abundance of coastal U.S. breeding colonies. NON-BREEDING: northern California, southwestern Arizona, Gulf Coast, and South Carolina southward through the breeding range. In the U.S., areas with the highest densities in winter include the Gulf Coast along the Texas-Louisiana border, the mouth of the Mississippi River, the lower Colorado River, and Florida (Root 1988). Wanders irregularly outside usual range; rare straggler to Hawaii.Provider: NatureServe  Source: NatureServe   CC License: by-nc

Conservation

Conservation Status

Populations appear to be declining along the Atlantic coast due to pollution and competition with other bird species. Egretta thula is at risk because of chemical contamination and the decline of wetland environments. Snowy egrets depend on wetland areas for food. Eggs in agricultural areas are contaminated by pesticides, which cause death. Egrets have also died from consumption of styrofoam, plastics, and lead found in the environment. Oil spills have also caused mortality. Egretta thula has been protected in North America since 1916 under the Migratory Bird Treaty Act. The Migratory Bird Treaty Act prohibited the hunting of egrets for their plumes, thus allowing them to return to their previous levels of abundance.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: appendix iii

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Management

Global Protection: Unknown whether any occurrences are appropriately protected and managed

Needs: Protect breeding sites and foraging areas.
Provider: NatureServe  Source: NatureServe   CC License: by-nc

Threats

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Threats include clearing of flood plain forests, loss and degradation of wetlands. Reduced reproductive success in Idaho was attributed to DDE residues accumulated in the nonbreeding season in Mexico (Findholt 1984).
Provider: NatureServe  Source: NatureServe   CC License: by-nc

Physical Description

Diagnostic Description

Differs from great egret in being much smaller (length 61 cm vs. 99 cm) and in having a black bill rather than a yellow one. Differs from immature little blue heron in having predominantly dark legs (vs. dull yellow), a slimmer mostly black bill (vs. two-toned with gray base and dark tip), and usually paler wing tips. Differs from cattle egret in being larger (length 61 cm vs. 51 cm), slim rather than stocky, and in having a black bill (vs. yellow or red-orange) and predominantly dark legs (vs. yellow or dusky-red). Differs from rare white-phase adult reddish egret in having yellow toes and lacking a two-toned pink-and-black bill.
Author: Hammerson, G., Provider: NatureServe  Source: NatureServe   CC License: by-nc

Morphology

Egretta thula is a medium-sized heron with a delicate build. Adult egrets generally measure between 56 to 66 cm and have a wingspan of approximately 100 cm. Egrets average 370 g in weight and the males tend to be slightly larger than the females. Egretta thula has entirely white plumage, a long, slender black bill, bright yellow lores, and long, slender black legs with bright yellow feet. Eyes are yellow. Breeding adults develop long, delicate plumes off their breast and are also characterized by their change in foot color, from yellow to orange. There are no overall differences in appearance between breeding populations, however, populations studied in North America and Central America are found to have a larger bill than egrets of South America.

Average mass: 370 g.

Average length: 56-66 cm.

Average wingspan: 100 cm.

Sexual Dimorphism: male larger

Average mass: 314 g.
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Size

Length: 61 cm

Weight: 371 grams
Author: Hammerson, G., Provider: NatureServe  Source: NatureServe   CC License: by-nc

Ecology

Associations

Egretta thula serves as a biological indicator of ecosystem health and habitat quality. In marshes, bays, and swamp habitats, the absence of egrets may reflect disturbances in the ecosystem, such as pollution, contamination of water, habitat loss, or human disturbance. In some habitats, researchers have sampled eggs and feathers to test levels of environmental contamination. Egrets are positioned at the top of the food chain, thus their decline may also infer a decline of other species, such as fish or insects. Egretta thula is a highly social bird and will not attack humans or disturb other bird species in its habitat.
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

General Ecology

Usually occurs in loose groups. Roosts usually communally.
Author: Hammerson, G., Provider: NatureServe  Source: NatureServe   CC License: by-nc

Habitat
Systems
  • Terrestrial
  • Freshwater
  • Marine
Author: BirdLife International, Compiler: BirdLife International, Provider: IUCN  Source: International Union for Conservation of Nature and Natural Resources   CC License: by-nc-sa

Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Migratory in north. Northern birds winter largely in Middle America (Stiles and Skutch 1989).
Author: Hammerson, G., Provider: NatureServe  Source: NatureServe   CC License: by-nc

Population Biology

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300
Provider: NatureServe  Source: NatureServe   CC License: by-nc

Trophic Strategy

Egretta thula prefers foraging habitats near bodies of shallow water, which are ideal for food sources. Its broad diet consists of earthworms, annelid worms, aquatic and terrestrial insects, crabs, shrimp, crayfish, snails, freshwater and marine fish, frogs, toads, lizards and snakes. The egret's diet is generally composed of 75% fish and 25% crustaceans. This egret has the widest range of foraging behaviors when compared to other herons. Food capturing is performed by pecking, walking slowly or quickly, running, hopping, hovering, and "disturb and chase" behaviors. Snowy egrets primarily feed during the early morning and evening hours. Egrets occasionally engage in group flights to fly to far-away foraging environments. Otherwise, egrets independently fly approximately 3 km from their colonies to foraging sites. However, foraging in larger groups allows for greater success in finding substantial food sources and helps provide protection from predators.

Animal Foods: amphibians; reptiles; fish; insects; mollusks; terrestrial worms

Primary Diet: carnivore (Piscivore )
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Life History and Behavior

Behavior

Egretta thula communicates through sound vocalizations and posture. Young birds produce soft, buzzing calls and mature birds produce high and low-pitched calls. High-pitched calls signify plentiful foraging sites and low-pitched calls signify aggressive situations. Greeting calls are common among egrets. Only males tend to use high sound vocalizations, especially to attract a female mate. Communication sounds are also used to defend the territory surrounding the nest. An egret's upright posture with fully erect feathers marks the onset of an attack on another bird.

Communication Channels: visual ; acoustic
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Cyclicity

Comments: Forages during daylight (Powell 1987).
Author: Hammerson, G., Provider: NatureServe  Source: NatureServe   CC License: by-nc

Life Cycle

Female egrets generally lay 3-6 eggs and both parents incubate the eggs for approximately 22-25 days. Upon hatching, the young nestling is a grayish color. It has a dark blue area around the eyes and the bill is a pale, pinkish gray. Once the eggs are fully hatched, the adults remove the eggshells from the nest. The hatchlings are covered in white down except for their wings. Pinfeathers appear by the first week. Juvenal feathers emerge on the body and wings by 2 to 3 weeks of age. Leg color varies from yellow to black. The hatchlings have a yellow colored bill tipped with black until five weeks of age, when the entire bill changes to black. Both parents brood their semialtricial young for the first 10 days. After 10 days, only one parent remains in the nest for 50% of the time. This generally lasts until the nestlings become 14 days old. The nestlings leave the nest after two weeks, but some may leave the nest as early as 10 days (Howell 1995; Parsons 2000).
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Life Expectancy

Egretta thula has a 71.6% mortality rate during its first year and a 31.4% mortality rate during years 2 to 17. The oldest egret was recorded in Utah and lived 22 years, 10 months. Snowy egrets generally live between 2 and 17 years. Egretta thula has been subject to nematode parasitism, which causes death. Starvation and inclement weather are likely causes of death for young nestlings.

Range lifespan

Status: wild:
22 (high) years.

Typical lifespan

Status: wild:
2 to 17 years.
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Reproduction

Breeding begins in late March or early April when the male egrets perform flight displays and sound vocalizations to attract female mates. The most common courtship display is the "Stretch" display, in which the male pumps his body up and down with his bill pointed towards the sky. The male then produces a call to attract females. The changing foot color from yellow to reddish orange indicates the beginning of breeding behaviors. Breeding adults are also characterized by the distinctive display of long, delicate plumes off their breasts. Once a male finds a mate, the pair performs sexual displays and eventually builds a nest for their offspring.

Mating System: monogamous

The male and female pair-bond is maintained through a series of sexual displays. Breeding begins in March or early April. Female egrets usually build nests in the territories defended by the males. Nests are often built in isolated, estuarine habitats and can be located either on the ground or as high as 30 feet in the trees. The nests are composed of woven twigs and small sticks that female egrets collect from the ground or steal from other nests. Egretta thula may also reuse old nests. These egrets are highly social nesters and build nests close to other egrets or herons. No preliminary rituals are performed prior to copulation, which takes place in the nest. Males stand on the backs of females and cloacal cavities come into contact during copulation to fertilize the eggs. The average duration of contact is 10 seconds. Females lay 3-6 eggs at a time (on average); eggs have a pale, greenish blue color. Incubation lasts 24 days on average and the chicks usually fledge 14 days after hatching. Young reach reproductive maturity after 1 to 2 years.

Breeding season: The breeding season begins in March or early April.

Range eggs per season: 2 to 8.

Average eggs per season: 3-6.

Range time to hatching: 22 to 29 days.

Average time to hatching: 24 days.

Range fledging age: 10 to 25 days.

Average fledging age: 14 days.

Range age at sexual or reproductive maturity (female): 1 (low) years.

Average age at sexual or reproductive maturity (female): 2 years.

Range age at sexual or reproductive maturity (male): 1 (low) years.

Average age at sexual or reproductive maturity (male): 2 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization (Internal )

Average eggs per season: 4.

Both parents incubate the eggs and feed the nestlings by dropping food into the nest. Once the eggs hatch, parents remove the eggshells from the nest. Both parents brood their altricial young continuously until the hatchlings are 10 days old. From 10 to 14 days, only one parent is present in the nest to brood the young. After 10 days, parents are only in the nest 50% of the time. However, when storms occur, the young are brooded continuously. During the first five days after hatching, parents feed their young by regurgitating food onto the nest floor for the hatchlings to eat. Sometimes the parents' bill is placed directly into the hatchlings' mouth and food is regurgitated. The younger nestlings are fed before the older hatchlings. Adults keep the nest clean by dumping waste over the sides of the nest.

Parental Investment: no parental involvement; altricial ; pre-fertilization; pre-hatching/birth (Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Molecular Biology and Genetics

Molecular Biology
The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 7 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

KBAR822-06|MACN-Or-ct 1567|Egretta thula| ------------------------------------------CTATACCTAATCTTCGGAGCATGGGCCGGTATAATTGGAACCGCCCTC---AGTCTCCTTATCCGAGCTGAACTTGGCCAGCCAGGAACGCTCCTAGGAGAC---GACCAGATCTATAATGTGATCGTCACCGCTCATGCCTTCGTAATAATCTTCTTCATAGTTATACCAATCATAATTGGGGGATTCGGAAACTGACTAGTACCACTCATA---ATTGGTGCCCCCGACATAGCATTCCCACGCATAAACAACATAAGTTTCTGACTCCTTCCACCATCATTTATACTCCTACTAGCCTCATCCACAGTCGAAGCAGGAGCAGGTACGGGCTGAACAGTCTACCCACCCTTAGCTGGCAACCTAGCCCATGCCGGAGCCTCAGTTGACCTA---GCCATCTTCTCCCTCCACTTAGCAGGGGTGTCTTCCATCCTAGGAGCAATCAACTTCATTACAACCGCCATCAACATAAAACCCCCAACCCTATCACAATACCAAACTCCCCTATTTGTATGATCCGTCCTAATTACCGCCGTTCTACTTCTACTTTCACTCCCAGTTCTCGCTGCA---GGTATTACAATACTACTAACTGATCGAAACCTAAACACCACATTCTTTGACCCCGCTGGAGGTGGCGACCCAGTCCTCTATCAACACCTATTCTGATTCTTCGGCCACCCAGAAGTCTATATTCTAATCCTA-------------------------------------------------------------------------------------------------------------------------------------------------------
-- end --

Download FASTA FileCompiler: Sujeevan Ratnasingham, Compiler: Paul D.N. Hebert, Provider: Barcode   Source: Barcode of Life Data Systems   CC License: by

Relevance to Humans and Ecosystems

Benefits

There are no known adverse affects of snowy egrets on humans.
Editor: Phil Myers, Museum of Zoology, University of Michigan, Editor: Alaine Camfield, Animal Diversity Web, Author: Andrea Weslosky, University of Michigan, Provider: The Regents of the University of Michigan and its licensors   CC License: by-nc-sa

Show/Hide iNaturalist Observations Map for this species. Source: iNaturalist