The Great Egret, catalyst of the conservation movement and symbol of the National Audubon Society, is breeding farther north in Canada as the planet warms.
By Rex Graham
The large, stunning bird is the featured species at the 2017 Great Louisiana BirdFest April 7-9 at a nature preserve near Mandeville. Along the Great Lakes and adjoining waterways in Canada, Great Egret numbers rose 679% during the 10 years ending in 2008.
“Such northward expansion could portend changes in distribution coinciding with changing climate,” researchers with Mississippi State University, Canadian Wildlife Services and the University of Minnesota said in the journal Avian Conservation and Ecology.
The Great Lakes from the Pigeon River in western Lake Superior, lakes Superior, Huron, Erie and Ontario and the upper St. Lawrence River once formed the northern limit of the Great Egret territory. But no longer.
Worldwide distribution of Great Egret
Worldwide, there are 4 subspecies of Ardea alba. In the Americas, the birds have nested near wetlands and ponds and along rivers from North Dakota on the north to southern Argentina on the south. In Africa the egrets are found south of the Sahara to the southern coast of South Africa. They also are found along most of the Mediterranean Coast of Africa and Europe. They also are found in the southern half of Asia, from the southern border of Russia to Indonesia, New Guinea and Australia.
Because of their ubiquity, the Great Egret is a species of “least concern” and attracts almost no research interest.
New Jersey Audubon Society researchers attached a solar-powered tracking transmitter to an egret that was subsequently dubbed “Edward the Egret.” He and another Great Egret drone called Clarence carry radio transmitters as part of an Audubon project to explore conservation successes in the New York-New Jersey harbor area.
However, even a ho-hum citizen-science project can generate a surprise. For example, most of the Great Egrets that breed in the U.S., Europe and northern China migrate south in the winter. Since they are big birds that fly slowly, researchers assumed migration would occur at a leisurely pace.
However, one afternoon in November 2015, Edward flew from New Jersey out over the Atlantic Ocean, turned south, and flew 14 hours parallel to the coast for 385 miles. He didn’t stop until he reached the Mattamuskeet National Wildlife Refuge in North Carolina.
On Edward’s return trip to New Jersey, he flew non-stop 494 miles, much of it at night.
In the breeding season, males and females grow their famously beautiful white bridal plumes that are gracefully curved at the tips. Males spend the most time displaying than females, but both use a repertoire of elaborate stretches, bows, crouches and twig shakes.
The most famous display is called the snap. With its bridal plumes (called aigrettes) fanned, the bird straightens its usually curved neck horizontally. It abruptly crouches, claps its mandibles, and flips its bridal plumes upwards. The display is repeated over and over.
You can find egrets wherever there are fish in shallow fresh, brackish or salt water. They are also fond of commercial fish ponds. They are opportunists and eat small mammals, amphibians, reptiles, birds and fish from 1 cm Gambusia to 1 kg Carp.
From the U.S. to Southeast Asia, egrets and other waterbirds have suffered from the intensification of agriculture, which usually involves the drainage of wetlands.
The lower esophagus of a Great Egret holds a finite volume of food. Since an egret parent wants to carry the maximum sized meal to its chicks, each foraging trip is designed to catch the maximum amount food in sizes that their growing chicks can swallow.
A study of radio-tagged egrets in Kansas near the Arkansas River revealed that spillways and other weirs provide the most fish. They nab fish as they swim upstream in the shallow waters of spillway weirs. Gizzard Shad captured here by egrets were 6 times heavier than fish caught along river banks or ponds. However, squabbling at weirs can be intense: scientists have reported 5 to 10 times more fighting there compared to less congested places.
Finding enough fish can be frustrating. In years of high rainfall in Kansas, the Arkansas River and its tributaries provided too many hiding places for fish. In a year with average precipitation, parents fly up to 18 km (5 mi) in search of food.
Dry weather fish bonanza
In a dry year in the Kansas study area, one radio-collared egret began flying 40 km to the same small area day after day
To find out what the egret was doing, scientists followed it to a dried up creek bed. It actually wasn’t completely dry. Schools of small fish were trapped in shallow pools.
“When this Great Egret was finally tracked to this site, it was one of a flock of about 25 wading birds that also included Snowy Egrets and Great Blue Herons,” Kansas and North Carolina researchers reported in the journal Waterbirds. “When the fish in one pool were depleted, the individuals moved to a different pool.”
In eastern Australia, some biologists are relying on old-school, on-site monitoring and Google maps to better understand egrets and other waterbirds.
Lake Eyre and the Murray-Darling Basin are called “breeding factories” for egrets, herons, and other waterbirds. However, a seemingly unimportant monitoring study of the farm ponds in the basin turned up a surprise.
Small farm ponds created by damming small, intermittent streams hold water for livestock to drink. In the Murray-Darling Basin, they account for only 0.71% of the surface water. However, monitoring field studies found an average of 16 birds per pond. Google satellite images show that the basin has 710,539 ponds.
Multiplying 16 birds by all those ponds, astonished researchers estimated that millions of waterbirds use on the ponds. (Great Egrets only nest in tall trees.)
“It is reasonable to suggest that farm dams are overlooked, and possibly very important, avian biodiversity hotspots,” the researchers from the University of Melbourne and the National School of Agronomy of Toulouse in France said in 2017 in the journal Avian Research. (They said much more study is needed to fully understand the ecological importance of farm ponds.)
Birding festival favorite
Where birdwatchers find egrets they usually find many other birds. At the Great Louisiana BirdFest, dozens of migratory bird species arrive from Mexico and South America. After crossing the Gulf of Mexico, the migrants rest along the U.S. Gulf Coast, especially Louisiana, before continuing north to their breeding territories.
Birders from around the world come to the annual BirdFest because it is considered one of the world’s premier birding festivals. Experts and novices sign up for the scheduled birding trips, social events, and the BirdFest’s “park crawl.”