Ardeidae

Many herons are instantly recognizable by their shape: an S-shaped neck (elongated sixth vertebra), long, bare legs, and daggerlike bill. This groups of wading birds has four subfamilies. The family has faced a variety of threats from human activity. Historically, adults, chicks, and eggs were collected for food, and fish-eating species were also killed as vermin (especially at fish hatcheries). During the late 19th and early 20th century, the use of herons' plumes in millinery trade decimated or exterminated populations of many species. Pesticides (such as DDT) and other environmental contaminants (such as mercury and selenium) have also adversely affected breeding success.

Additional information

Most species grow elongated ornamental plumes on the head, chest, breast, or scapulars prior to the breeding season. These plumes may be lanceolate (featherlike) or filamentous (hairlike). The most extreme form are 'aigrettes', which are wispy and ethereal in appearance. Agami Heron (Agamia agami) has unique sickle-shaped plumes on the sides of the neck. All species have paired patches of powder down, primarily on the breast and rump; the number of pairs varies by subfamily. These continuously growing feathers deteriorate at the tips, forming a powder that the bird spreads over its feathers when preening, to help maintain the feathers in good condition.

Most species are conspicuous. Many are highly social or gregarious, while others are generally solitary. However, the behavior of many species can be extremely flexible to take advantage of fluctuating food availability, with individuals able both to be solitary, to defend a feeding territory, or to participate in conspecific flocks or mixed-species flocks of other wading birds (including ibis and storks). Some species are reclusive and easily observed; in particular bitterns are known to 'freeze', relying on their cryptic coloration to avoid detection.

All species spear or seize prey with their bill; however, they employ a variety of foraging strategies. Most stalk by stealthy, slow walking or wading, or by waiting poised and motionless at the water's edge. Others hunt in shallow water, wrapping their wings around their head to form a shaded canopy to attract prey, or actively flapping their wings to flush the prey. Some species stir their feet to flush prey from beneath the substrate, or even entice prey closer by moving their colorful toes. Birds of the genus Butorides have been documented to use live bait (such as insects and worms) to inanimate items to lure fish. Herons do not swim, but individuals can learn to forage over deeper water by hovering or even landing on the water's surface, or by shallow diving to spear prey under the surface. The birds can compensate for light refraction in water by moving their head back and forth to ascertain the distance to the prey. Most species are aquatic, but a few are more terrestrial.

Taxonomy

Number of genera: 19

Number of species: 65

This groups of wading birds has four subfamilies, which are classified by similarities of morphology, powder down configuration, and behavior:

• Ardeinae (herons, night herons, egrets, and pond herons) 
• Tigrisomatinae (tiger herons)
• Botaurinae (bitterns) 
• Cochleariinae (Boat-billed Heron, Cochlearius cochlearius)

A list of all species can be found here.