(COCOI HERON.)
+Ardea cocoi+, _Burm. La-Plata Reise_, ii. p. 508 (Paraná, Tucuman,
Cordova); _Scl. et Salv. Nomencl._ p. 125; _Hudson, P. Z. S._
1875, p. 625 (Buenos Ayres); _Durnford, Ibis_, 1877, p. 189
(Buenos Ayres), et 1878, p. 399 (Patagonia); _Gibson, Ibis_,
1880, p. 158 (Buenos Ayres); _White, P. Z. S._ 1883, p. 41
(Cordova); _Barrows, Auk_, 1884, p. 271 (Entrerios).
_Description._--Above grey; head above, wings, and tail plumbeous
black; beneath white, neck and sides of belly striped with black:
whole length 36·0 inches, wing 18·0, tail 7·0. _Female_ similar.
_Hab._ North and South America.
In size, form, and colour the Cocoi closely resembles the Common Heron
of Europe; in flight, language, and feeding-habits the two species
are identical, albeit inhabiting regions so widely separated. In the
southern part of South America it is not seen associating with its
fellows, nor does it breed in heronries; but this may be owing to
the circumstance that in the temperature countries it is very thinly
distributed, and it is highly probable, I think, that in the hotter
regions, where it is more abundant, its habits may not appear so
unsocial. Though they are always seen fishing singly, they pair for
life, and male and female are never found far apart, but haunt the same
stream or marsh all the year round. Azara says that in Paraguay, where
it is very scarce, it goes in pairs and breeds on trees. On the pampas
it makes its solitary nest amongst the rushes, and lays three blue eggs.
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.
Birds ever fly reluctantly from danger; and all species possessing the
advantage of a long neck, such as the Swan, Flamingo, Stork, Spoonbill,
&c., will continue with their necks stretched to their utmost capacity
watching an intruder for an hour at a time rather than fly away. But
in the Herons it must be only by a great effort that the neck can
be wholly unbent; for even if the neck cut out from a dead bird be
forcibly straightened and then released, it flies back like a piece of
india-rubber to its original shape. Therefore the effort to straighten
the neck, invariably the first expression of alarm and curiosity, must
be a painful one; and to keep it for any length of time in that position
is probably as insupportable to the bird as to keep the arm straightened
vertically would be to a man. Thus the Heron flies at the first sight of
an intruder, whilst the persecuted Duck, Swan, or other fowl continues
motionless, watching with outstretched neck, participating in the alarm
certainly, but not enduring actual physical pain.
Doubtless in many cases habits react upon and modify the structure
of parts; and in this instance the modified structure has apparently
reacted on and modified the habits. In seeking for and taking food,
the body is required to perform certain definite motions and assume
repeatedly the same attitudes; this is most frequently the case in
birds of aquatic habits. A facility for assuming at all times, and an
involuntary falling into, these peculiar attitudes and gestures appears
to become hereditary; and the species in which they are the most
noticeable seem incapable of throwing the habit or manner off, even when
placed in situations where it is useless or even detrimental. _Tringæ_
rapidly peck and probe the mud as they advance; Plovers peck and run,
peck and run again. Now I have noticed scores of times that these birds
cannot possibly lay aside this habit of pecking as they advance; for
even a wounded Plover running from his pursuer over dry barren ground
goes through the form of eating by pausing for a moment every yard or
so, pecking the ground, then running on again.
The Paraguay Snipe, and probably other true Snipes, possesses the
singular habit of striking its beak on the ground when taking flight.
In this instance has not the probing motion, performed instinctively as
the bird moves, been utilized to assist it in rising?
Grebes on land walk erect like Penguins and have a slow awkward
gait; and whenever they wish to accelerate their progress they throw
themselves forward on the breast and strike out the feet as in swimming.
The Glossy Ibis feeds in shallow water, thrusting its great sickle beak
into the weeds at the bottom at every step. When walking on land it
observes these motions, and seems incapable of progressing without
plunging its beak downwards into imaginary water at every stride.
The Spoonbill wades up to its knees and advances with beak always
immersed, and swaying itself from side to side, so that at each lateral
movement of the body the beak describes a great semicircle in the
water; a flock of these birds feeding reminds one of a line of mowers
mowing grass. On dry ground the Spoonbill seems unable to walk directly
forward like other birds, but stoops, keeping the body in a horizontal
position, and, turning from side to side, sweeps the air with its beak,
as if still feeding in the water.
In the foregoing instances (and I could greatly multiply them), in which
certain gestures and movements accompany progressive motion, it is
difficult to see how the structure can be in any way modified by them;
but the preying attitude of the Heron, the waiting motionless in
perpetual readiness to strike, has doubtless given the neck its very
peculiar form.
Two interesting traits of the Heron (and they have a necessary
connexion) 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 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. An old naturalist has suggested, as
a reason for this, that the Heron, from its peculiar manner of taking
its prey, requires fair weather to fish--that during spells of bad
weather, when it is compelled to suffer the pangs of famine inactive, it
contracts a meagre consumptive habit of body, which subsequent plenty
cannot remove. A pretty theory, but it will not hold water; for in this
region spells of bad weather are brief and infrequent; moreover, all
other species that feed at the same table with the Heron, from the
little flitting Kingfisher 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.