The cause of the nocturnal singing of birds that do not go abroad during the night and are strictly diurnal in all their other habits has never been satisfactorily explained. It is natural that the Whippoorwill, which is a nocturnal bird, should sing during his hours of wakefulness and activity. There is also no difficulty in explaining why Ducks and Geese, and some other social birds, should utter their loud alarm-notes, when they meet with any midnight disturbance. These birds usually have a sentinel who keeps awake; and if he give an alarm, the others reply to it. The crowing of the Cock bears more analogy to the song of a bird, for it does not seem to be an alarm-note. This domestic bird may be considered, therefore, a nocturnal songster, if his crowing can be called a song; though it is remarkable that we seldom hear it during evening twilight. The Cock sings his matins, but not his vespers; he crows at the earliest dawn of day, and at midnight upon the rising of the moon, and whenever he is awakened by artificial light. Many singing-birds are accustomed to prolong their notes after sunset to a late hour, and become silent only to commence again at the earliest daybreak. But the habit of singing in the night is peculiar to a small number of birds, and the cause of it forms a curious subject of inquiry. By what means are they enabled to sustain such constant watchfulness, singing and providing subsistence for their offspring during the day, and still continuing wakeful and musical while it is night? Why do they take pleasure in singing, when no one will come in answer to their call? Have they their worship, like religious beings, and are their midnight lays but the outpouring of the fervency of their spirits? Do they rejoice, like the clouds, in the presence of the moon, hailing her beams as a pleasant relief from the darkness that has surrounded them? Or in the silence of night, are their songs but responses to the sounds of the trees, when they bow their heads and shake their rustling leaves in the wind? When they listen to the streamlet, that makes audible melody only in the hush of night, do they not answer to it from their leafy perch? And when the moth flies hummingly through the recesses of the wood, and the beetle sounds his horn, what are their notes but cheerful responses to these sounds, that break sweetly upon the quiet of their slumbers?