The black horse fly is probably a pioneer, density independent, organism. It is able to live in many diverse types of habitats, including meadows, open grasslands, marshy areas or near slow streams.

Density-dependent factors:

None known.

The black horse fly and the cattle egret can be found in The Woodlands of Texas near Houston. This is a forested area of mixed hardwoods and pines with patches of swamp. Low tier plants include many types of wildflowers, dewberries, American beauty berries, muscadine grapes, yaupon, clover and grasses. Trees include: loblolly pines, many varieties of oak (including live oak and water oak), American holly, and sweetgum. There are a great many types of insects and other larger animals that live in the forest. Some areas have been semi-cleared for residential areas farms and ranches, but these are edged with remnants of the forest. The cattle egret can be found in the drainage ditches, ponds and near or on the backs of cattle (on ranches). The black fly could also be found in these areas.

The female black horse fly sucks blood from large mammals (cattle, horses, etc.). The male sucks nectar.

The cattle egret eats mainly insects, particularly grasshoppers and locusts, also butterflies, beetles, dragonflies, flies and maggots from dumps and slaughterhouses. But truly, their food tastes are all inclusive: small animals (weaker birds, their eggs and hatchlings, mice, snakes, lizards, frogs, fish, earthworms) and even grains (barley, peas and hay).

The cattle egret is mainly a secondary consumer but can also be a primary, tertiary, and quaternary consumer.

BIBLIOGRAPHY

Campbell, Neil A., Biology. The Benjamin/Cummings Publishing Company, Inc., Menlo Park, California, 1996.

D’Vora Ben Shaul, "Beautiful, Yet A Bother," Jerusalem Post, Dec. 8, 1995.

Line, Les, "African Egrets? Holy Cow!" International Wildlife, Vol. 25. Nov. 1, 1995.

The Audubon Society Field Guide to North American Birds: Western Region, Alfred A. Knopf, New York, 1977.

Density-independent factors:

A freeze in the fall or winter may kill some population members or slow them down.

The cattle egret seems to be limited by very little. They have been very successful because of their ability to emigrate and inhabit varied types of habitats. They also consume a wide variety of foods including all sorts of insects, small animals (frogs, etc.) and grains.

Density-dependent factors:

Suitable nesting sites might be a limiting factor for the cattle egret. In certain ecosystems the taller trees might become over- crowded. Their roosting colonies are "usually filthy, smelly, and noisy...and tend to kill the trees hosting it" (because of the heavy nitrates in the birds’ excrement) which may have a limiting effect on nesting sights also. Information as to whether or not this causes their population growth rates to decline is not readily available but it does not appear to be true. They do take advantage of a variety of ungulates and are more successful in their foraging on the backs of some animals more than others, this may be a limiting factor. It is thought that the birds arriving in South America from Africa were able to take advantage of newly cleared tropical forests for ranches that provided "bovine hosts on a continent that otherwise lacked large grazing animals." (Les Line, 1995)

Density-independent factors:

Cold climates seem to keep them from nesting.

The black horse fly has an opportunistic life history. It breeds at maximum capacity, has a short life cycle and high reproduction rate.

Limits of Geographical Distribution

The black horse fly is not known to be limited by geographical area. It is known in North America from Quebec to Florida, west to New Mexico and north to the Pacific Northwest.

The cattle egret has an opportunistic life history and has benefited from the agricultural activities of man. They forage for insects, taking advantage of whatever livestock happens to be around: cows, horses, sheep, goats, geese, and in the African wilds: buffalos, zebras, wild-beests and waterbucks even bulldozers at a garbage dump, to help them out by stirring up insects in the area. They eat a varied diet which besides insects includes: fish, frogs, snakes, lizards, mice, barley, peas and hay.

Their life histories may be slightly skewed toward equilibrium because they are known in the South to arrive after the native heron species have established their nesting sites.

The cattle egret is definitely not restricted by its prey and therefore has no known geographical limitations, although it is not known to breed in the northern Canadian provinces. A native of Africa, it is believed to have arrived in the United States as early as 1941. These birds have colonized parts of North and South America without human help and members of the species are still routinely sighted at sea flying from West Africa to northeastern South America. The cattle egret today, has colonies in 42 states and probably arrived in Texas around 1959 where it moved in with colonies of native herons.