over, and the result desired is obtained, a period with new duties commences. During the first few days after hatching, most birds rarely leave their young for long, and then only to procure food for themselves and their family. In cases of great danger, both parents bravely defend their offspring. As soon as the first period of helplessness is over, and the young have grown somewhat, they are carefully taught to shift for themselves; and it is only when they are perfectly capable of so doing that they leave the nest and the parents."[278] The bird family is usually monogamic, and the marriage is lasting. Birds are generally faithful to the marriage vow; and this is particularly true of the females.[279] "With the exception of those belonging to the gallinaceous family, when pairing," they do so "once for all till either one or the other dies.[280] And Dr. Brehm is so filled with admiration for their exemplary family life that he enthusiastically declares that 'real genuine marriage can only be found among the birds.'"[281] [275] _Ibid._, 22. [276] WESTERMARCK, _op. cit._, 9 ff. [277] BREHM, _Tierleben: Allgemeine Kunde des Tierreichs_ (10 vols., Leipzig and Vienna, 1891). Vols. IV-VI are devoted to birds. See also his _Bird-Life_ (London, 1874). [278] WESTERMARCK, _op. cit._, 11; _cf._ BREHM, _op. cit._, IV, 19 ff., _passim_; and HERMAN MÜLLER'S _Am Neste_, which Brehm has used. [279] DARWIN, _Animals and Plants under Domestication_, II, 81, speaks of pigeons as being "true to their wedding-vow." On polygyny and monogamy among animals see _idem_, _Descent of Man_, 216 ff. "Many mammals and some few birds are polygamous, but with animals belonging to the lower classes I have found no evidence of this habit. The intellectual powers of such animals are, perhaps, not sufficient to lead them to collect and guard a harem of females" (216, 217). Birds sometimes lose the pairing "instinct" under domestication (220). Regarding the "marital virtue" of birds, see HELLWALD, _op. cit._, 30.