Herons
Herons
Herons, egrets, and bitterns are large, slender wading birds in the family Ardeidae, order Ciconiiformes (which also includes anhingas, storks, spoonbills, and ibises). Most of the species in the heron family have long legs, necks, and bills. These characteristics are all adaptive to hunting their prey of fish, amphibians, snakes, small mammals, and other animals living in the shallow waters of wetlands. The prey is generally caught by grasping it firmly in the mandibles, and is then killed by beating it against the ground, branches, or another hard substrate. The food is usually then rinsed, and swallowed head-first.
Herons have an unusual articulation of the sixth vertebra that is adaptive to swallowing large prey. This feature causes the neck of herons to adopt a distinctive, S-shape when they are in flight or resting, although their neck can be extended while grooming or to give greater reach while attempting to catch prey.
Herons also have an unusual type of filamentous feathers, known as powder-down. These feathers are very friable, and disintegrate into a powder that the bird rubs over the major body feathers to cleanse them of slime from its food of fish.
Herons primarily occur along the edges of lakes and other shores, and in marshes, swamps, and other relatively productive wetlands. Many species in the heron family are colonial nesters, generally on islands, if possible. These birds typically build platform nests of sticks in trees, sometimes with many nests in a single, large tree.
Species of herons
Sixty-two species are included in the heron family, occurring worldwide, except in Antarctica and arctic North America and Eurasia. Twelve species of herons breed regularly in North America. One of the most familiar is the great blue heron (Ardea herodias), occurring over most of the temperate and more southern regions of North America, as well as in parts of Latin America. The great white heron used to be considered a separate species (under A. occidentalis ), but it is now regarded as a color variety of the great blue heron that only occurs in the Florida Keys and nearby parts of Florida Bay. The great blue heron breeds in colonies of various sizes, usually nesting in trees. The great blue heron is very similar to the gray heron (A. cinerea), which has a widespread distribution in Eurasia and Africa. Further studies may conclude that these are, in fact, the same species.
Smaller species of herons include the Louisiana or tricolored heron (Egretta tricolor), and the little blue heron (Egretta caerulea), found in the wetlands of the coastal plain of southeastern North America, the Caribbean, and the Pacific coasts of Mexico. The green-backed heron (Butorides virescens) is a relatively small and attractive species with a wide distribution in southern North America. Some individuals of this species have learned to “fish,” using floating bits of material, such as small twigs, to attract minnows. These birds will deliberately drop their “bait” into the water and may retrieve it for re-use if it floats away.
The black-crowned night heron (Nycticorax nycticorax) is widely distributed in colonies throughout much of the United States and a small region of southern Canada. The yellow-crowned night heron (Nyctanassa violacea) is more southeastern in its distribution than the preceding species, and it tends to occur more frequently near saltwater.
The largest of the several species of egrets in North America is the common or American egret (Casmerodius albus), ranging widely over the southern half of the continent. The snowy egret (Leucophyx thula) is a smaller, more southern species. Most species of herons and egrets are patient hunters; they quietly stalk their prey or lie in wait for food to come within their grasp. However, the relatively uncommon reddish egret (Egretta rufescens) is an active hunter on saline mudflats of the southernmost states, where it runs boisterously about in active pursuit of its food of small fishes and invertebrates.
The American bittern (Botaurus lentiginosus) inhabits marshes over much of temperate North America and further south. This species has a resounding, “onk-a-tsonck” call that can be heard in the springtime when male birds are establishing breeding territories and attempting to attract a mate. The least bittern
(Ixobrychus exilis) is the smallest North American heron. Both of these bitterns are very cryptic in their reedy, marshy habitats. When they perceive that they are being observed by a potential predator, these birds will stand with their neck and bill extended upright, with the striped breast plumage facing the intruder, and they will even wave their body sinuously in concert with the movement of the surrounding vegetation as it is blown by the wind.
The cattle egret (Bubulcus ibis) is a naturalized species in the Americas, having apparently colonized naturally from Africa in the present century. This species was first observed in Argentina, but it has since spread widely and now occurs in suitable habitat throughout South, Central, and North America. The cattle egret commonly follows cattle in pastures, feeding on the arthropods and other small animals that are disturbed as these large animals move about.
Conservation of herons
Most species in the heron family, and many other types of birds, were unsustainably hunted during the nineteenth century to provide feathers for use in the millinery trade, mostly as decorations on ladies’ hats and other clothing. Many millions of herons and egrets were killed for this reason, and their populations declined precipitously in most regions. The outcry among conservationists over the slaughter of so many birds for such a trivial purpose led to the formation of the National Audubon Society in the United States in 1886 and the Royal Society for the Protection of Birds in Great Britain in 1889. These were the first important, non-government organizations that took up the conservation and protection of natural biodiversity as their central mandate.
Today, habitat losses are the most important threat to species in the heron family and to other birds of lakes, shores, and wetlands. These habitat types are suffering worldwide declines from pollution, drainage, conversion to agriculture or urban development, and other stressors associated with human activities. As a result, the populations of herons, egrets, and bitterns are declining in North America and in many other regions, as are other wildlife with which these birds share their wetland habitats.
Birds in the heron family are large, attractive, and sometimes relatively tame. Consequently, they are popular among birders; however, the numbers of these beautiful and charismatic birds have declined as a result of continuing influences of humans, especially damage caused to wetlands. In the future, the populations of these birds can only be sustained if sufficiently large areas of their natural habitats are preserved.
Resources
BOOKS
del Hoyo, J., A. Elliott, and J. Sargatal. Handbook of the Birds of the World. Vol. 1, Ostriches to Ducks. Barcelona: Lynx Edicions, 1992.
Ehrlich, P.R., D.S. Dobkin, and D. Wheye. Birds in Jeopardy. Stanford, CA: Stanford University Press, 1992.
Forshaw, Joseph. Encyclopedia of Birds. 2nd ed. New York: Academic Press, 1998.
Hancock, J., and J. Kushlan. The Herons Handbook. London: Croom Helm, 1984.
Kushlan, J., and H. Hafner. Heron Conservation. New York: Academic Press, 2001.
Kushlan, J., and J.A. Hancock. The Herons: Ardeidae. Oxford: Oxford University Press, 2005.
Marquis, M. Herons. London: Colin Baxter, 1993.
Heron Specialist Group. Heron Bibliography. <http://www.tourduvalat.org/news_1293.htm;jsessionid=a616919f6c904ab78709e6865e81bc52> (accessed November 1, 2006).
Bill Freedman