Wildlife

Great White Heron

Ardea (herodias) occidentalis

Description

39-52" (99-132 cm). W. 5'10" (1.8 m). A common large, white heron with a orange to yellowish bill. The Great White Heron is presently considered a white form of the Great Blue Heron and includes intermediate forms between the Great Blue Heron and the Great White Heron. The Great White Heron differs from the Great Egret in being larger, with greenish-yellow rather than black legs.

Habitat

Great White Herons nest primarily on isolated mangrove islands in either loosely formed colonies, commonly with the blue morph; in colonies of other wading birds including Roseate Spoonbills, Reddish Egrets, Double-crested Cormorants, and Brown Pelicans; or as solitary pairs.

Nesting

Great White Herons generally build flat stick platforms up to 1.2 m (4 ft) in diameter, located from approximately 1 m (3 ft) to 6 m (20 ft) high in a variety of shrubs and trees, predominantly in red and black mangroves and some tropical hardwood species. Clutches range from 2 to 5 but usually number 3 or 4, pale bluish-green eggs, and incubation lasts approximately 30 days (Robertson 1978b). Young birds fledge at approximately 7 to 8 weeks of age and remain around the nesting key for another month, after which they disperse north out of Florida Bay and settle into a variety of coastal and inland habitats. In the Keys, Great Whites breed throughout the year, with peak nesting occurring from November through February. Some individuals are known to breed several times per calendar year

Range

Great White Herons nest only in southern Florida, predominantly on islands in Biscayne Bay, throughout Florida Bay, the lower Keys, and the Marquesas. One or 2 nests have been documented annually since 1981 in Cortez and Terra Ceia bays near Bradenton, and another nesting occurred on ABC Islands, Marco Island in 1976, 1979, and 1988. One nest was found at Hemp Key in Lee County in 1969, but no additional nests are known from that area. Nesting by Great White Herons has also been observed in the northern Ten Thousand Islands.

Voice

A harsh squawk.

Discussion

  Great White Herons are a state-listed Species of Special Concern. In Florida Bay, the population recovered from only a few individuals in the mid-1930s to, in the 1960s, a stable population of between 800 to 900 birds in summer and 1,200 to 1,400 birds in winter. However, during that period, fluctuations occurred due to hurricane-related mortality. Surveys in the mid-1980s indicated population numbers similar to those of the 1960s. The Florida Bay birds are thought to comprise about 60% of the total Florida Keys population. In Florida Bay, between 450 and 600 nests were documented annually from 1987 to 1990. From aerial surveys in the late 1980s, covering about half of the lower Keys, 74 to 241 active nests have been observed during the peak December breeding period. Reproduction was monitored on 55 islands throughout Florida Bay from 1987 to 1990. Colony sizes and locations were similar among years. However, nesting success varied among colonies, and differences between regions were consistent for all years. The influence of people feeding herons accounts for some of the differences. A large portion of the birds nesting in the eastern region of the bay, the "panhandlers" fly to residential canals and shorelines of the mainline Keys where they supplement their diet with food from humans. Between 71 to 84% of nests produced at least 1 young in the eastern bay, compared with 28 to 63% for other regions of the bay. Approximately 1 young per active nest was produced at monitored sites in the Great White Heron Refuge in the lower Keys in 1989.