The vagabond egret

StoryImage( ‘/Images/Story//Auto-img-1112803963801.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘The cattle egret is becoming a familiar sight in the Rock River Valley.’);

As I wander around the Rock River Valley these days, it seems that the cattle egret is becoming more and more a familiar sight. This white bird with the short neck, yellow bill, and stocky body is usually seen scratching around in a field not far from a group of foraging cattle or other livestock.

Many do not realize that a generation ago, this relative of our native snowy and great egrets was not present in Illinois. In fact, it was not even a member of the bird fauna of North America. Being a native of Africa, this vagabond species did not cross the Atlantic Ocean and become established in Central and South America until late in the 19th century. It was first observed in this country in 1952, when seven breeding pairs showed up in Florida. Within the next 10 years, it became the most abundant egret in North America, nesting in all but 10 of the continental United States. It has also been spotted in Alberta, Ontario, Newfoundland, and the Northwest Territories of Canada.

For birds, as with airplanes, the flight eastward across the Atlantic is considerably easier than the return westward flight into the teeth of the prevailing westerly flowing air currents. In fact, approximately 52 species of our land and fresh water birds have been recorded in Europe, usually during migration periods and often during or at the end of periods of strong westerly winds. The cattle egret and the rare fieldfare, however, are the only Old World birds known to have navigated successfully the Atlantic against the wind and established themselves in the New World in recent times without the direct assistance of man.

The impressive range extensions of this nomad probably depend on inherited instincts as well as ecological good luck. That the bird has a strong instinct for venturing far and wide is supported by many observations. For example, in 1963 one was seen on St. Paul’s rocks, midway between Africa and Brazil. In 1972, one landed on a fishing trawler on the Newfoundland Grand Banks, some 300 miles from land. In addition to its inclination to seek greener pastures, the wanderer has another strong instinct that helped it settle successfully on our shores.

In its native home, the cattle egret is a commensal of African antelopes, elephants, buffaloes, and other foraging animals. In a commensal relationship such as this, the egret becomes associated with another animal for feeding purposes. The other animal gains nothing from this association, but the commensal is benefited by having its food unwittingly catered. As the egret invaded other continents, it found a ready-made, unoccupied ecological niche as a commensal of cattle and other livestock. Unlike our native egrets, the cattle egret likes to dine on terrestrial insects such as grasshoppers, crickets, beetles, and a host of other forms found in fields.

As livestock meander about their range munching on plants, they unknowingly are acting as “beaters” when they stir up insects for the waiting birds. Cows, sheep, and goats do not routinely feed on bugs, so the cattle egret’s feeding preferences in no way interfere with those of the livestock. Occasionally, an egret is observed to be doing a cow a favor by perching on its back and deftly plucking an embedded tick from the cowhide, a practice undoubtedly appreciated by the cow.

The establishment of this egret in the Americas has apparently been without ecological consequences. In many instances, when an alien species invades a new ecosystem, the results have been catastrophic. Without any established natural enemies or other means of population control, the invader quickly multiplies to the detriment of the native species and forces it from its ecological niche, sometimes to extinction. We have only to recall what happened when the Japanese beetle, Asian ladybird beetle, grass carp, kudzu vine, zebra mussel, fire ant and a host of other aliens were introduced to this country and found (what we termed in the Army) the land of the big PX.

So far, we are lucky in that the cattle egret has presented us with no ecological problems, and it is nice to have this beautiful bird as an addition to our avifauna.

From the April 6-12, 2005, issue

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