The following general remarks on the Heron apply chiefly to the Ardea cocoi, and to some extent also to other species of the Heron family.
I have observed Herons a great deal, and think that there is much to be said in support of Buffon’s opinion that they are wretched, indigent birds, condemned by the imperfection of their organs for a perpetual struggle with misery and want.
Much as the different species vary in size, from the Ardea cocoi to the diminutive Variegated Heron of Azara (Ardetta involucris), no bigger than a Snipe, there is yet much sameness in their conformation, language, flight, nesting and other habits. They possess a snake-like head and neck, and a sharp taper beak, with which they transfix their prey as with a dart—also the serrate claw, about which so much has been said, and which has been regarded as an instance of pure adaptation. A curious circumstance has come under my observation regarding Herons. Birds in poor condition are very much infested with vermin; whether the vermin are the cause or effect of the poor condition, I do not know; but such is the fact. Now in this region (the Argentine Republic) Herons are generally very poor, a good-conditioned bird being a very rare exception; a majority of individuals are much emaciated and infested with intestinal worms; yet I have never found a bird infested with lice, though the Heron would seem a fit subject for them, and in the course of my rambles I have picked up many individuals apparently perishing from inanition. I do not wish to insinuate a belief that this immunity from vermin is due to the pectinated claw; for though the bird does scratch and clean itself with the claw, it could never rid the entire plumage from vermin by this organ, which is as ill adapted for such a purpose as for “giving a firmer hold on its slippery prey.”
The Spoonbill has also the serration, and is, unlike the Heron, an active vigorous bird and usually fat; yet it is much troubled with parasites, and I have found birds too weak to fly and literally swarming with them.
I merely wish to call the attention of ornithologists to the fact that in the region where I have observed Herons they are exempt in a remarkable degree from external parasites.
Much has also been said about certain patches of dense, clammy, yellowish down under the loose plumage of Herons. These curious appendages may be just as useless to the bird as the tuft of hair on its breast is to the Turkey-cock; but there are more probabilities the other way, and it may yet be discovered that they are very necessary to its well-being. Perhaps these clammy feathers contain a secretion fatal to the vermin by which birds of sedentary habits are so much afflicted, and from which Herons appear to be so strangely free. They may even be the seat of that mysterious phosphorescent light which some one has affirmed emanates from the Heron’s breast when it fishes in the dark, and which serves to attract the fish, or to render them visible to the bird. Naturalists have, I believe, dismissed the subject of this light as a mere fable without any foundation of fact; but real facts regarding habits of animals have not unfrequently been so treated. Mr. Bartlett’s interesting observations on the Flamingoes in the Society’s Gardens show that the ancient story of the Pelican feeding its young on its own blood is perhaps only a slightly embellished account of a common habit of the bird.
I have not observed Herons fishing by night very closely, but there is one fact which inclines me to believe it probable that some species might possess the light-emitting power in question. I am convinced that the Ardea cocoi sees as well by day as other diurnal species; the streams on the level pampas are so muddy that a fish two inches below the surface is invisible to the human eye, yet in these thick waters the Herons fish by night and by day. If the eye is adapted to see well with the bright sun shining, how can it see at night and in such unfavourable circumstances without some such extraneous aid to vision as the attributed luminosity?
Herons, of all birds, have the slowest flight; but though incapable of progressing rapidly when flying horizontally, when pursued by a Hawk the Heron performs with marvellous ease and grace an aerial feat unequalled by any other bird, namely, that of rising vertically to an amazing height in the air. The swift vertical flight with which the pursued ascends until it becomes a mere speck in the blue zenith, the hurried zigzag flight of the pursuer, rising every minute above its prey, only to be left below again by a single flap of the Heron’s wings, forms a sight of such grace, beauty, and power, as to fill the mind of the spectator with delight and astonishment.
When the enemy comes to close quarters, the Heron instinctively throws itself belly up to repel the assault with its long, crooked, cutting claws. Raptorial species possess a similar habit; and the analogous correlation of habit and structure in genera so widely separated is very curious. The Falcon uses its feet to strike, lacerate, and grasp its prey; the Heron to anchor itself firmly to its perch; but for weapons of defence they are equally well adapted, and are employed in precisely the same manner. The Heron, with its great length of neck and legs, its lean unballasted body, large wings, and superabundance of plumage, is the least suited of birds to perch high; yet the structure of the feet renders it perfectly safe for the bird to do so. Thus the Heron is enabled to sit on a smooth enamelled rush or on the summit of a tree, and doze securely in a wind that, were its feet formed like those of other Waders, would blow it away like a bundle of dead feathers.
Another characteristic of Herons is that they carry the neck, when flying, folded in the form of the letter S. At other times the bird also carries the neck this way; and it is, indeed, in all long-necked species the figure the neck assumes when the bird reposes or is in the act of watching something below it; and the Heron’s life is almost a perpetual watch. Apropos of this manner of carrying the neck, so natural to the bird, is it not the cause of the extreme wariness observable in Herons? Herons are, I think, everywhere of a shy disposition; with us they are the wildest of water-fowl, yet there is no reason for their being so, since they are never persecuted.