Beyond the fact already pointed out of their resemblance to the Cranes and Rails, the Herons form a relatively compact and generally well known group. They have long or moderately long legs, the front of the metatarsus being covered with scute-like plates. There are always four toes, the hind toe being on the same plane as the others, and the claw of the middle one is comb-like on the inner side. The body is thin and compressed, the neck usually long, and the bill long and pointed, with all the outlines nearly straight. The wings are relatively large, but are very much rounded from the fact that the second, third, and fourth quills are of nearly the same length. The lores and a space about the eyes are bare. “The general plumage, which is very variable in color, is soft and loose; the feathers on the crown of the head, back, and upper breast being frequently elongated.” The peculiar powder-down patches on the rump, abdomen, and elsewhere are always present and constitute a well known character of the group.
In the matter of distribution, Herons are almost cosmopolitan, being, however, most abundant in tropical and subtropical regions. They are inhabitants for the most part of swamps and marshes, a few only preferring the seacoast. They are often gregarious, feeding and nesting in communities, where they build large, bulky nests, frequently in trees. They may often be seen walking about in or along marshes with a slow and measured gait; when on the wing their progress is rather slow, although strong, and is accompanied by a continuous flapping of the wings. In general they lay from three or four to six unspotted eggs, which are bluish green or whitish in color.
The group is an old one, some half a dozen species having been found fossil, the oldest being from the lower Eocene of England. A single fossil species (Ardea paloccidentalis) has been found in North America, and another (A. Megacephala) has disappeared in comparatively recent times from the island of Rodriguez.
Over one hundred living species are known, distributed, according to Sharpe, among thirty-seven genera, but this number of genera is perhaps excessive, since the differences between some of the groups seem hardly worthy of full generic rank. North America possesses some eighteen forms, these being lately referred by American ornithologists to no less than eleven genera, most of which were formerly accorded only subgeneric rank.
The true Herons belong to the genus Ardea and number some dozen or more species. They are quite variable in size, ranging from twenty-eight to fifty-six inches in length; in color there is likewise considerable variation. Of the habits of Herons in general, Hudson, in his “Argentine Ornithology,” says: “Two interesting traits of the Heron (and they have a necessary connection) are its tireless watchfulness and its insatiable voracity; for these characters have not, I think, been exaggerated even by the most sensational of ornithologists. In other birds of other genera, repletion is invariably followed by a period of listless inactivity during which no food is taken or required. But the Heron digests his food so rapidly that, however much he devours, he is always ready to gorge again; consequently he is not benefited by what he eats, and appears in the same state of semi-starvation when food is abundant as in times of scarcity. . . . All other species. that feed at the same table with the Heron, from the little flitting King-fisher to the towering Flamingo, become excessively fat at certain seasons, and are at all times so healthy and vigorous that, compared with them, the Heron is the mere ghost of a bird. In no extraneous circumstances, but in the organization of the bird itself, must be sought the cause of its anomalous condition; it does not appear to possess the fat-elaborating power, for at no season is any fat found on its dry, starved flesh;’ consequently there is no provision for a rainy day, and the misery of the bird (if it is miserable) consists in its perpetual, never satisfied craving for food.”