The procedure is unquestionably instinctive. The sounds uttered by young birds are sufficiently definite to be readily recognized and are susceptible of classification. In domestic chicks at least six notes may be distinguished. First the gentle “peeping” note, expressive of contentment. A further low note, a double sound, seems to indicate extreme satisfaction and pleasure. Very characteristic and distinct is the danger-note--a sound difficult to describe, but readily recognized. If a humble-bee, a black-beetle, a big worm, a lump of sugar--anything strange and largish--be thrown to the chicks, this danger-note is at once heard; and it serves to place others on the alert, though this is perhaps the outcome of experience. Then there is the cheeping sound, expressive apparently of a state of mild dissatisfaction with the present state of affairs. It generally ceases when one throws some grain, or even stands near them. Extreme dissatisfaction is marked by a sharper, shriller squeak, when one seizes them against their inclination. Lastly, there is the shrill cry of greater distress, when, for example, their swimming powers are subjected to critical examination. With pheasants a gentle, “peeping” note of contentment, a shriller cry of distress, and a danger-note, generically like, but specifically distinct from, that of the chick, are early differentiated. The complaining note of the partridge is uttered six or seven times in quick succession, followed by a pause. The note of the plover is high-pitched, and much like the familiar cry of the adult bird, to which it owes its popular name of “peewit.” So, too, the guinea-fowl in down utters from the first notes quite characteristic of its kind, while its danger-note is not unlike that of the chick or pheasant. The piping of ducklings is comparatively monotonous, and there does not seem to be a definite danger-note. With moor-hen chicks, even on the first day, two notes are well-marked--a call-note, lower in pitch than that of the chick, and rather harsh and raucous, and a “tweet, tweet” of pleasure, something like the contented note of a canary. Later, five or six notes are differentiated, the most characteristic of which is the harsh “crek, crek,” when the little bird is from any cause excited. It is uttered in a crouching attitude, with head thrown back and wings held outwards and forwards, waving to and fro in a very characteristic manner. That this has suggestive value for other moor-hen chicks is shown by its distinctly infectious effect; if one bird has cause to utter the note and strike the attitude others follow suit. While clearly instinctive in their mode of occurrence, while they seem to show well the co-operation of an internal emotional factor, their biological value seems to lie in their suggestive effect on other members of the brood. They form an elementary but sufficient social bond.