Bubulcus ibis
The Cattle Egret is widespread and still extending its range worldwide except in extreme climates (polar areas, tundra, boreal forests, mountains, and deserts). Historical changes in distribution are dynamic and complex, but well-documented (Koes and Taylor 2006, Telfair 1983, 1993, 1994, 2006). In North America, the Cattle Egret occurs throughout the United States north to southern Canada and south throughout Mexico, Central America, and the West Indies. Breeding is confirmed in all but 4 of the contiguous U.S. states (Montana, New Hampshire, Washington, and West Virginia), and has also beern confirmed in 3 Canadian provinces (Manitoba, Ontario, and Saskatchewan). Cattle Egret was introduced to Hawaii in 1959 and has become established.
In Texas, Cattle Egrets breed throughout the entire coastal and eastern regions, eastern portions of north central and central prairies, and a few scattered sites in the south plains, west Edwards Plateau, and Trans-Pecos. Some birds also winter in the state, most along the coast, especially the middle and lower regions; but, some years far inland. Most Trans-Pecos records have been of birds seen during migration or during post-breeding dispersal (Swepston 1983 and pers. comm.).
DISTRIBUTION. Texas Colonial Waterbird Census summaries (Texas Parks and Wildlife Dept/Tex. Colonial Waterbird Soc. 1981- 1992) and the TBBA (1987-1992) reveal Cattle Egrets breed in all coastal and 68 inland counties (Telfair 1983, 1993). They have established colonies within 266 heronries since 1959. The mean number of colonized heronries per county is 3.3 (2.3 inland, 6.9 coastal). The number of colonized heronries per region is: 148 inland (61 northeast, 60 southeast, 19 north central, 4 south, 4 west) and 118 coastal (73 upper, 39 central, 6 lower). About 71% of the Cattle Egret population nests inland (35% northeast, 18% central, 17% southeast, and 2% south) and the remaining 29% nest along the coast (16% upper and 13% central).
National Audubon Society Christmas Bird Counts have recorded wintering Cattle Egrets in Texas since 1956 However, no marked birds were reported; thus, it is not possible to determine whether wintering egrets are permanent residents or migrants.
SEASONAL OCCURRENCE. The breeding season for the Cattle Egret is long, extending from April (1st eggs) to mid-September (last fledglings) with some late nesting in some years extending into October. However, peak breeding occurs during June and July. The earliest egg date reported by the TBBA was May 15; the latest date for eggs was June 26. The latest date for nests with young was August 16. Previous research has recorded early and late dates for eggs of April 10 and September 1, respectively (Telfair 1979, 1983).
BREEDING HABITAT. In Texas, the Cattle Egret nests in multi-species heronries established by other heron species; they do not establish their own heronry. Colony size may vary from fewer than 100 to over 15,000 pairs. Nest sites are of wide variety and substrates with much variation in physiognomy and floristic composition. There are 4 types of heronries in which they nest: 1) woodlands- upland woods or mottes with or without adjacent streams or ponds, 2) swamps-trees and shrubs in water, 3) inland wooded islands-trees and shrubs on islands in inland waters, and 4) coastal islands-trees, shrubs, and herbaceous vegetation on natural islands and dredge-material deposit islands.
Depending upon the site and vegetation, nest heights may vary from ground level to about 9 m (30 ft). Nests are shallow saucers or bowls, flimsy or solid, with much variation. Only about 0.5% of nests are built on platforms remaining from the previous year. The nest is composed of 2-3 parts, a lower platform foundation of robust sticks, an upper layer of smaller twigs or vines, often bearing fresh leaves, and an occasional lining of herbaceous materials. The smallest, most poorly constructed nests are probably of first-time breeders. Nests are untidy and coarse; chick excrement flows into interstices cementing the nest into a solid structure.
Some large multi-species colonies are reestablished annually for as many as 30+ years, but others are not. The reasons for this difference are unknown. Some of the large colonies are considered nuisances when they are located near human habitation (Telfair et al. 2000).
STATUS. Although adult and immature Cattle Egrets were observed in Texas from 1954-1958, nesting was not confirmed until 1959 when at least 10 pairs and probably another 14 pairs were found (J. R. Dixon, pers. comm.; Webster 1959, 1960). The first non-breeding sight records were from the coastal prairie and upper to lower coast. The first nesting records were from the upper and lower coasts and southeast inland area. The origin of these birds is unknown, but they probably came from the east via coastal Louisiana rather than from the south via coastal Mexico (Telfair 1983). Breeding began in the northeast in 1963. Colonies radiated from these regions and between 1973 and 1988 most of the present breeding range was occupied. Since 1987, a few colonies have been established north along the Red River and to the west and south along the Rio Grande. Also, since 1987, in response to unusual wet periods, especially 1987 and 1992, small colonies of Cattle Egrets and other associated colonial waterbirds have nested in west Texas (Upper and Lower Panhandle, South Plains, and Trans-Pecos regions) County record breeding range expansion was mapped (Telfair 1993, Telfair et al. 2000).
Between 1959-1976, as a result of annual influx of immigrant breeding birds, the population increased steeply at an average annual rate of 51.9%. Between 1976-1990, the rate decreased greatly to 2.57% annually apparently the result of heronry saturation. The rate of increase for the entire period of 1959-1990 was 29.6%. However, since Cattle Egrets usually nest later than most native species with which they associate, many pairs breed after survey periods. So, the peak breeding population may have reached about 580,000 pairs (Telfair et al. 2000).
Spread of the Cattle Egret in Texas has been very uniform. A mean of 2.5 ± 1.5 new counties were colonized per year. Inland distribution of these birds appears to be determined by the location of heronries containing Little Blue Herons (Egretta caerulea) and Snowy Egrets (E. thula) whose distribution is probably determined by the availability of crayfish – major food items for their young (Telfair 1981). Coastal distribution is determined by the location of heronries containing Snowy Egrets and Tricolored Herons (E. tricolor).
Large colonies of Cattle Egrets began to develop in 1964. After 1973, some heronries began to be abandoned. This abandonment resulted from the accumulation of guano which thinned or killed nest-site vegetation; but, heronries in guano-tolerant vegetation were not abandoned. Thus, new heronries are established more often (Telfair et al. 2000).
Although Cattle Egrets feed primarily on grasshoppers and crickets, which they obtain by associating with grazing cattle, no apparent relationship exists between the distribution or density of grazing cattle and the egret’s breeding range, distribution, or size of heronries in which they breed. Also, no apparent relationship exists between their breeding range and maximum abundance and availability of grasshoppers and crickets (Telfair 1983).
By the early 21st century, Cattle Egrets were considered common to abundant summer residents throughout most of Texas (Lockwood and Freeman 2004). A Breeding Bird Survey (BBS) route in Anderson County on the boundary between the Pineywoods and Post Oak Savannah and Blackland Prairies regions had an average annual count of 741 Cattle Egrets on the 40 km (25 mi) route, the 2nd highest in the United States and Canada (Price et al. 1995). Unfortunately, comprehensive inland annual breeding censuses have not been conducted since 1990. However, coastal data between 1973-2000 were analyzed by McFarlane (2002). He found an annual decreasing trend of -1.85%. Also, since 1980, breeding populations have declined between -1.8 to -2.9% in the Blackland Prairies, Post Oak Savannah, East Texas Forests, and Central Coastal Prairie ecoregions (Sauer et al. 2005, Telfair 2006).
Text by Raymond C. Telfair II (2006)
Literature cited.
Koes, R. F. and P. Taylor. 2006. Prairie provinces (Fall migration). N. Am. Birds 60: 91-92.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Price, J., S. Droege, and A. Price. 1995. The summer atlas of North American birds. Academic Press, New York.
Swepston, D. A. 1983. Notes on the Cattle Egret in the Trans-Pecos region of Texas. Bull. Texas Ornithological Soc. 16: 30-32.
Telfair, R. C. II. 1979. The African Cattle Egret in Texas and its relation to the Little Blue Heron, Snowy Egret and Louisiana Heron. Ph.D. diss., Texas A&M Univ., College Station.
Telfair, R. C. II. 1981. Cattle Egrets, inland heronries, and the availability of crayfish. Southwest. Nat. 26: 37-41.
Telfair, R. C. II. 1983. The Cattle Egret: a Texas focus and world view. Kleberg Stud. Nat. Resour.Tex. Agric. Exp. Stn., Texas A&M Univ., College Station.
Telfair, R. C. II. 1993. Cattle Egret (Bubulcus ibis) Population trends and dynamics in Texas (1954-1990). Nongame and Urban Programs, Fish & Wildl. Div., Texas Parks & Wildl. Dept. PWD-RP-N-7100-234, Austin.
Telfair, R. C. II. 1994. Cattle Egret (Bubulcus ibis). In The Birds of North America, No. 113 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Telfair, R. C. II, B. C. Thompson, and L. Tschirhart. 2000. Nuisance heronries in Texas: characteristics and management. 2nd ed. Wildl. Diversity Prog., Wildl. Div., Texas Parks and Wildl. Dept. PWD BK W7000-134 (1/00).
Telfair, R. C. II. 2006. Cattle Egret (Bubulcus ibis). The Birds of North America (A. Poole, Ed.). Ithaca: Cornell Laboratory of Ornithology; Retrieved from The Birds of North America Online database: http://bna.birds.cornell.edu/BNA/account/Cattle Egret/.
Telfair, R. C. II, D. A. McCrimmon, Jr., and S. T. Fryska. 2000. Population dynamics of the Cattle Egret in Texas, 1954-1999. Waterbirds 23: 187-195.
Webster, F. S., Jr. 1959. South Texas region (fall migration, winter season, and nesting season). Audubon Field Notes 13: 46-47, 307, 442.
Webster, F. S., Jr. 1960. South Texas region (nesting season). Audubon Field Notes 14: 462.