The habit of coming together for dancing and of decorating the places where the birds habitually perform their dances is, of course, well known from the pages that Darwin gave to this subject in The Descent of Man (ch. xiii). Visitors of the London Zoological Gardens also know the bower of the satin bower-bird. But this habit of dancing seems to be much more widely spread than was formerly believed, and Mr. W. Hudson gives in his master-work on La Plata the most interesting description, which must be read in the original, of complicated dances, performed by quite a number of birds: rails, jacanas, lapwings, and so on.

The habit of singing in concert, which exists in several species of birds, belongs to the same category of social instincts. It is most strikingly developed with the chakar (Chauna chavarris), to which the English have given the most unimaginative misnomer of "crested screamer." These birds sometimes assemble in immense flocks, and in such cases they frequently sing all in concert. W.H. Hudson found them once in countless numbers, ranged all round a pampas lake in well-defined flocks, of about 500 birds in each flock.

"Presently," he writes, "one flock near me began singing, and continued their powerful chant for three or four minutes; when they ceased the next flock took up the strains, and after it the next, and so on, until once more the notes of the flocks on the opposite shore came floating strong and clear across the water— then passed away, growing fainter and fainter, until once more the sound approached me travelling round to my side again."

On another occasion the same writer saw a whole plain covered with an endless flock of chakars, not in close order, but scattered