Egretta thula
snowy egret

Egretta thula is found throughout North, Central, and South America as well as the Caribbean. It breeds in coastal and inland wetlands, but its range limits have changed over time due to the effects of hunting and habitat loss. Small breeding populations are located in Nova Scotia, Canada, and more heavily populated locations are found across the United States. Egretta thula is common among northern Nevada, Utah, and southeastern states, especially Florida and states bordering the Gulf of Mexico. This egret is most prevalent throughout Mexico, Central America, and South America. Egretta thula is a partially migratory species, as it relocates from its northern habitats of the United States and Canada to its winter ranges located in Mexico, Central America, South America, the West Indies, and Bermuda. Snowy Egrets begin their northward migration in early March and depart in September to migrate to their wintering areas. (Parsons and Master, 2000)

Egretta thula generally prefers an environment of shallow water inlets for feeding purposes. Salt-marsh pools, tidal channels, shallow bays, and mangroves are among the most preferred habitats in North America. Habitats are most common among coastal areas and islands due to the availability of stable and abundant food sources. During the winter months, egrets migrate to the Caribbean to nest and roost in the mangroves. The Caribbean is home to other favorable egret habitats including salt-water lagoons, freshwater swamps, grassy ponds, beaches, shallow reef areas, flooded rice fields, and wet grassy meadows. Throughout Central America, E. thula prefers mainly lowland areas near freshwater swamps, lakes, and large river mouths. South American species also prefer coastal mangroves, mudflats, and swamps rather than highland areas. (Howell and Webb, 1995; Parsons and Master, 2000)

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. (Chandler, 1997; Howell and Webb, 1995; Parsons and Master, 2000)

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. (Chandler, 1997; Parsons and Master, 2000)

Egretta thula walks upright with its wings held close to its body. This upright posture is ideal for foraging, because it allows the egret to make quick directional changes to catch its prey. They are most active at dawn and dusk (crepuscular); they have flying capabilities but do not swim. Snowy egrets engage in various self-maintenance behaviors that include grooming their wings, head-scratching to remove insects on their body, and bathing. Egretta thula spends most of the day resting. Males protect the nesting territories. Egretta thula is a highly social bird that engages in group foraging with other aquatic bird species. Group interaction with other bird species is also common in nesting territories. Snowy egrets avoid predators such as owls, hawks, poisonous snakes, and raccoons. (Parsons and Master, 2000; Robbins, 1966)

Home Range

We do not have information on home range for this species at this time.

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. (Howell and Webb, 1995; Parsons and Master, 2000)

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. (Howell and Webb, 1995; Parsons and Master, 2000)

Egretta thula has shown an increased preference for island nest sites in urbanized, coastal estuaries. Egrets choose urbanized locations over isolated locations, because isolated locations have more predators. Egrets use flight to escape predation from terrestrial animals and they are known to have innate recognition and avoidance of poisonous snakes.

Known predators include: Procyon lotor (racoon), Bubo virginianus (great-horned owl), Strix varia (barred owl), Corvus brachyrhynchos (American crow), Corvus ossifragus (fish crow), Alligator mississippiensis (American alligator), Elaphe obsoleta (rat snake) and Buteogallus anthracinus (common black-hawk). (Parsons and Master, 2000)

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. (Robbins, 1966)

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

In the United States from 1880 to 1910, adult egrets were shot by plume hunters. Egretta thula was hunted for its delicate back plumes that were used to decorate women's hats and clothing. In 1886, plumes were valued at $32 per ounce, which was twice the price of gold at the time. In 1910, most hunting ceased due to citizens' requests to stop the slaughter of egrets. However, hunting still continued in Central and South America due to the European demand for plumes. (Parsons and Master, 2000)

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. (Parsons and Master, 2000)

Similar species to Egretta thula include Egretta caerulea, little blue heron, and Egretta garzetta, little egret. Little blue herons have completely white plumage, but can be distinguished from E. thula by their gray lores. Little egrets are larger and stockier than E. thula and also have longer legs, bill, and neck. (Parsons and Master, 2000)