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April 2020

Vol. 48, No. 2

Front Cover: April 2020

Snowy Egret by John Sill


Snowy Egret by John Sill © Massachusetts Audubon Society. Courtesy of the Museum of American Bird Art.

ABOUT THE COVER ARTIST

John Sill is a freelance wildlife artist living in the mountains of North Carolina. He was the illustrator for the Bird Identification Calendar for Mass Audubon for many years. His work has appeared in Birds In Art at the Leigh-Yawkey Woodson Art Museum, Wausau, Wisconsin, and in Art of the Animal Kingdom at the Bennington Center for the Arts in Vermont. He continues to illustrate the "About" and "About Habitats" series of natural history books for children written by his wife Cathryn.

Snowy Egret

The Snowy Egret (Egretta thula) in its elegant breeding plumage is as bright and spectacular as its early human history is dark and unsettling. During the last two decades of the nineteenth century and the first decade of the twentieth, Snowy Egrets were relentlessly hunted during breeding season for their nuptial plumes to decorate ladies’ hats. The Snowy Egret was pushed to the brink of extinction. The passage of the Migratory Bird Treaty Act of 1918 ended the slaughter of the plume trade in the United States but it continued in South America for some time. The recovery of the species has been remarkable. In Massachusetts, it was a rare vagrant until the 1950s when Snowy Egrets first nested, and they have gradually increased in numbers since then.

The Snowy Egret is a medium-sized heron with white plumage. Breeding adults have black bills and legs and bright yellow feet and lores. Nonbreeding birds have greenish yellow feet, the color extending up the back of the legs, and have gray in the bill. During breeding season, adults have long, elegant, plumes on their breast, back, and crown that are the basis for the spectacular nuptial displays that characterize the species, and at the height of the breeding season, the yellow of the lores and feet turn orangish to bright red. Immature Little Blue Herons also have white plumage but have gray lores, a gray bill tipped with black, and lack the yellow slippers. Two poorly defined subspecies are generally recognized. E. t. thula is found in eastern North America, Central, and South America; E. t. brewsteri, with a larger bill, is restricted to western North America. Individual variations in all populations make regional comparisons difficult.

Some Snowy Egret breeding populations are migratory, for example, in the East along the coast from Maine to Maryland. Year-round populations are found along the coast from Maryland south through Florida and the Caribbean Islands, west along the Gulf Coast to Texas, on both coasts of Mexico, and Central America. Migratory breeding populations also occur in scattered small areas across the United States with several located in the Great Lakes region. Other such populations occur in larger areas across East Texas and Oklahoma, east to Georgia, and in the west across Nevada and into several other western states. Several populations of year-round breeders also occur in California. Most wintering birds occur along the coast of California and in patches throughout Mexico and Central America. In late summer after breeding, Snowy Egrets may disperse widely; they have been recorded throughout the United States and southern Canada. In Massachusetts, the Snowy Egret is considered a locally common breeder and a common to occasionally abundant migrant. It can also be a common summer visitor. Snowy Egrets arrive in Massachusetts from late March to May, with numbers peaking in late August and early September. In the fall, they leave by November.

Snowy Egrets are probably seasonally monogamous. Pair formation occurs at the nest site where males perform a variety of nuptial displays that often showcase their remarkable plumes. The most prominent is the stretch display with bill pointed skyward and the body pumped up and down while uttering a wah-wah-wah call. Aerial displays include a version of the stretch display, and circle and tumbling flights. One bird may jump over the other. Males also give a gurgling call. Aggressive displays include crest-raising accompanied by rasping calls. Attacks may be made with body held forward and plumes fully erected.

Snowy Egrets breed in mixed species colonies, often on isolated offshore islands near their estuarine tidal foraging areas. They frequently utilize dredge-spoil islands. Away from the coast, they may nest on islands in freshwater lakes, marshes, swamps, and along rivers. Breeding colonies in Massachusetts are largely on offshore islands. Most nests are on large tree branches six feet or more from the ground, but also occur in shrubs and occasionally on the ground. Females do most of the nest building, often with material brought in by the male. The nest is composed mostly of sticks and twigs and is lined with grass and moss, typically with a shallow depression. Both parents incubate the 3–5 greenish blue eggs for the 22–24 days until hatching. At hatching, chicks are covered with down but are helpless. Both parents incubate the chicks for about 10 days until the chicks can leave the nest. Both parents feed the nestlings, initially regurgitating well-digested food onto the floor of the nest and later directly into the chick’s bill. The chicks often disperse at about age two weeks and remain in or near the colony for up to two months.

Snowy Egrets often forage in mixed-species flocks in salt marshes and tidal pools, channels, and flats and in the South among mangroves. They are more versatile feeders than any other North American heron with a broad spectrum of foraging behaviors that include disturbing and chasing, standing, walking slowly or quickly, running, hopping, foot-stirring, and in flight, hovering and dipping. They also leapfrog feed, where birds at the rear of the foraging flock fly to the front. Many of their foraging behaviors take advantage of their bright yellow feet, which apparently act as lures to prey. Snowy Egrets feed mostly on small fish and crustaceans but take a wide variety of prey, including earthworms, insects, frogs, snakes, and crabs.

Nesting Snowy Egrets experience nest predation by raccoons, snakes, owls, and crows. Islands have become the favored location for breeding colonies in Massachusetts due to limited access by mammalian predators. Nestlings are also at risk from pesticides and storms, and other heron species may occasionally lay their eggs in Snowy Egret nests. Individual breeding colonies are subject to fluctuations in breeding success, but the dramatic population recovery in the twentieth century and the shift to predominantly island breeding suggests that the Snowy Egret is adaptable and likely secure.

William E. Davis, Jr.


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