see an insect which has been inserted in the mouth of a nestling, withdrawn, minced with the bill, and offered again. When behavior is free the return to the nest (b), is prompt and direct, but birds will frequently pause at some point near by and look about as if for assurance. The black-billed cuckoo if timid or suspicious, will sometimes stand on such a perch with insect in bill for five or ten minutes without uttering a sound, but occasionally pumping its tail, stretching its head and looking cautiously around, or again it will remain perfectly quiet like a statuette. The actual path which is now taken to the nest is eventually
determined by habit. The bird flies to a certain branch, grasps certain twigs, before it finally lands on a certain part of the nest itself. Then usually follows a pause as the bird straightens up and stands over her young. If the mate is brooding, as is likely to be the case in bad weather, a call-note is sometimes given by the visiting bird, when the sitter promptly retires. This note is often heard in the absence of the mate, when it serves as a stimulus to the young. Further the sitter, if a cuckoo, always detects the approach of the visiting bird by hearing, if not by sight, so that the whole family is practically never seen together at the nest, contrary to what often happens with gulls, robins, cedar-birds, kingbirds, or some of the warblers. The young detect the approach of the parent by sight or sound, or by the vibration imparted
