One of the more familiar sites in the Texas coast is the presence
of an elegant white bird known as the cattle egret or Bubulcus
ibis (L.). These birds are considered to be both a beneficial
insect predator as well as a nuisance to people and property.
The cattle egret is native of the Old World, common from Africa east to India, north to northern China and South to Australia. It was first reported to occur in the new world by 1877 in British Guiana. From there it expanded its range, island-hopping to Florida by 1942. Since then, the egret population has been exploding throughout the southeastern United States probably due to the lack of natural enemies and relatively little competition from native animals of the new world (Snoddy 1969).
These white birds reportedly arrived in the Texas in the early 1950's. One account (Rubin, 1983) claims that cattle egrets were brought into the state in 1953 by Texas ranchers who saw their insect-eating habits as a boon for the cattle industry. Regardless of their means of reaching the state, they were nesting on Galveston Island by 1958 (Long 1979).
That cattle egrets feed on insects is commonly known, but few scientific studies have quantified the egrets' feeding behavior. Snoddy' 8 ( 1959) surveys of egrets in the Okefenokee Swamp, Georgia, produced the following observations:
The egrets tended the cattle daily from soon after sunrise until late afternoon. The number of cattle egrets observed with each animal varied but commonly averaged two per animal. Egrets walked very near the cattle, picking insects from the animals and surrounding vegetation. They pecked horse flies and other nuisance flies from the cattle's lower extremities and regularly perched upon the animals backs to feed. The cattle did not appear belligerent nor disturbed by the presence of the egrets. In fact, the cattle apparently encouraged the egrets' association by moderating tail-switching and other "fly fighting" behavior while egrets were feeding on their backs.
An analysis of stomach contents of egrets collected and dissected at a rate of 5 birds per week from August 15 to October 16 revealed their diets. On the average, by numbers of specimens recovered, egrets consumed 59% horse flies, 28% grasshoppers and crickets, 5% tree frogs, 4% spiders, 2% dragon flies, 0.8% stable flies, 0.1% ticks and 0.1% undetermined organisms. The average number of horse flies per egret stomach was 51.5! Certainly the egrets diet will be influenced by the abundance of insect species present in the areas where the birds are feeding.
Examination of bird's bodies revealed that apart from a species of louse fly and several undetermined species of bird lice, "no ectoparasites of cattle were found on the cattle egrets". Thus, the study concluded that the cattle egrets potential as a control agent for both forage insects and cattle ectoparasites apparently outweighs its potential threat as a purveyor of parasites and/or diseases of cattle.
The impact of cattle egrets on diseases spread by insect vectors of Texas livestock has not been documented. However, one can speculate that disease organisms such as Anoplasmosis marginale of cattle, spread primarily by horse flies and ticks (Alderink and Dietrich 1983), have not benefited from the egrets' presence.
Not everyone is happy about the egrets, particularly those living near rookeries or colony nests--like the one in the dead trees over Lake Texana near Hwy 59 in Jackson County. In Avinger, Texas, the birds, numbering 25,000, outnumber humans by 40 to 1. Residents are outraged by the invasion, particularly since the birds are sheltered by two international treaties as well as federal and state laws. Those harassing the birds face fines.
Marvin Parvino, Mayor of Avinger was quoted as saying: "These birds stink, they're noisy and they pose a threat to community health". The rookery is ankle deep in bird droppings, eggs fall from the trees like leaves and shrubbery is coated with rotting yolks. Dead baby birds litter the ground. Fine feathers fill the air and the stench of ammonia hangs over the woods like a cloud. (Rubin 1983). Although state health officials say no serious illness attributable to egrets has been confirmed, the nuisance and indirect potential from insects and insect transmitted diseases associated with rookies has not been studied.
Whether or not the benefits outweigh the hazards of their presence, the egrets are here to stay. In agriculture, the bird's presence is often put to another good use--as insect scouts in rice fields and pastures. The presence of cattle egrets in fields can be an excellent indicator of the presence of armyworm hotspots.
Alderink, F. J. and A. Dietrich. 1983. "Economic and epidemiological implications of anoplasmosis in Texas beef cattle herds". Texas Agricultural Experiment Station B-1426. Texas A&M University, College Station, Tx. 16 PP.
Long, P. F. 1979. Cattle egret: a good bird to have around. Farmland news, Ag. 31, p. 19.
Rubin, S. 1983. Birds outnumber residents, take over small town. Bryan-College Station Eagle, Aug. 7, p 2AA.
Snoddy, E. L. 1969. On the behavior and food habits of the cattle egret, Bubulcus ibis (L.). J. Georgia Entomol. Soc. 4(4):156-158.
The USER is always responsible for the effects of pesticide residues on his livestock and crops, as well as problems that could arise from drift or movement of the pesticide from his property to that of others. Always read and follow carefully the instructions on the container label.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.
Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.
1989
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Last modified: March 18, 1997 by Edgar Cross