Breeding Bird Atlas 1 Species Accounts

Cattle Egret
Bubulcus ibis

Egg Dates

late May to first week of July

Number of Broods

one; may re-lay if first attempt fails.
If reproductive vigor, adaptability, and achievement of transoceanic dispersal are measures of success, the Cattle Egret may be nominated as the world’s avian winner. This species probably evolved in the seasonally flooded plains of tropical Africa, where it was forced to feed exclusively on land during the dry season and became a commensal of the African Buffalo. It is theorized that irrigation projects in Africa induced a population explosion beginning early in this century and set the stage for the emigration of "surplus" birds across the Atlantic. The Cattle Egret was first recorded in South America around 1880 and began dispersing toward North America via two routes: north through Central America and from island to island across the Antilles. Cattle Egrets may have reached Florida by 1930, but the first documented North American record was a bird collected in Wayland, Massachusetts, on April 23, 1952. The species is now cosmopolitan between the 45° north latitude and 45° south latitude and is apparently continuing its expansion toward the poles. In eastern North America, it breeds mainly along the coast, north to Maine and Nova Scotia, and is also established at Lake Champlain.

Cattle Egrets increased steadily as annual visitors to Massachusetts beginning in the late 1950s. A total of 155 were seen in the state on May 5 to 17, 1964, and over 100 were seen at single localities in the early 1970s (Veit & Petersen 1993). The first breeding record for Massachusetts was during the Atlas period in July 1974 at House Island, Manchester. The 2 to 4 pairs present in 1974 had increased to 10 pairs by 1976; however, between 1978 and 1980, the House Island colony was abandoned. In 1982, 5 nests were found on Eagle Island, and 2 pairs were seen there in 1984. During the Atlas period, Cattle Egrets were also discovered nesting on Clark’s Island in Plymouth Bay, but this site was also abandoned. The breeding population in Massachusetts has yet to exceed a total of 10 pairs at two sites.

Migrants now are recorded regularly throughout the state and have been seen in every month except February. Cattle Egrets return to Massachusetts in April (late March in mild seasons). Males establish territories within mixed colonies containing Snowy Egrets, Black-crowned Night-Herons, and possibly other species. They are very vocal and aggressive and defend territory against conspecifics and other species with a variety of threat displays. The most intense of these is the "full forward threat" in which, with head, chest, and back plumes fully erected, the male crouches and lunges at intruders with bill agape while uttering a rasping kowwh-kowwh call. There are also an "upright threat display" (Palmer 1962) and a variety of other calls. The territories defended by Cattle Egrets are said to be notably smaller (and colonies more dense) than those of other heron species.

The beginning of breeding activity is marked by the appearance of intense changes in soft-part colors. Males at first react to females with an aggressive "bill snap display" (Palmer 1962) while extending the head and neck downward and outward. This is followed by a "stretch display," accompanied by an ow-roo call. Females carefully watch displaying males and eventually single out a favorite. After pair formation, nest building begins with the males gathering materials and the females placing them. These roles are occasionally reversed. Members of a pair use ritualized greeting ceremonies when they meet at the breeding site. The typical nest has a base of large twigs topped by smaller ones but contains no fine lining materials. The finished structure is a rather crude, shallow cup 8 to 17.5 inches in diameter. It is usually placed in shrubbery or high in small trees. The two to five (usually four or five) pale blue-green eggs are laid at
1- or 2-day intervals, 5 to 10 days after pairing, and incubation requires another 16 to 22 days. The young hatch at 1-day intervals, and the youngest and smallest nestlings are allowed to languish if food is in short supply. The young leave the nest at 20 days after hatching, fledge at 30 days, and become fully independent in 45 days.

There is little specific information available for the nesting of the Cattle Egret in Massachusetts. In 1977, the Clark’s Island breeders were on eggs the first week of July (Parsons). Six Vermont egg dates from Lake Champlain range from May 13 to June 26. A New York nest 5 feet up in Catbrier contained five eggs on June 7 and two nestlings on July 7, and 3 other nests had five young each on June 9.

When not on the breeding islands, Cattle Egrets typically feed on insects (especially grasshoppers) in dry pastures, but they are also very much at home in flooded meadows, where they prefer frogs to fish. Their habit of following cattle and other domestic grazing animals and catching the insects flushed by their benefactors is as famous as their great recent emigrations, and the worldwide increase in lands cleared for livestock may account in part for the ability of the species to establish itself so readily. Whether or not they deliberately and routinely pick ticks from the hides of their commensals is still debated.

Family groups of Cattle Egrets may be seen feeding together in local cow pastures for a brief period in late summer, during which time they return to the nesting island to roost, but the breeding area is deserted by late August. Dispersing and migrating Cattle Egrets occur in variable numbers in fall, mainly in eastern Massachusetts, including as many as 44 counted in Ipswich and South Dartmouth in August 1976 (Veit & Petersen 1993). The wintering grounds of the state’s breeders is unknown, but most of the population winters from Florida south to South America.

Map Legend and Data Summary

Atlas 1 data collected from 1975-1979
rare and local; always associated with large coastal heronries
Note: rare and local; always associated with large coastal heronries
Christopher W. Leahy