the uniting or joining in couples. The instinct of pairing is bestowed on every species of animals to which it is necessary for rearing their young, and on no other species. All wild birds pair; but with a remarkable difference between such as place their nests on trees, and such as place them on the ground. The young of the former, being hatched blind, and without feathers, require the nursing care of both parents till they are able to fly. The male bird feeds his mate on the nest, and cheers her with a song. As soon as the young are hatched, singing yields to a more necessary occupation, that of providing food for a numerous issue; a task which requires the care of both parents.
Eagles and other birds of prey build upon trees, or in other inaccessible spots. They not only pair, but continue in pairs all the year round; and the same pair produces year after year. This at least is the case of eagles. The male and female hunt together, unless during incubation, at which time the female is fed by the male. A greater number than a single pair are never seen in company.
Gregarious birds pair, in order probably to prevent discord in a society confined to a narrow space. This is the case particularly with pigeons and rooks. The male and female sit on the eggs alternately, and divide the care of feeding their young.
Partridges, plovers, pheasants, sea-fowl, grouse, and other kinds that place their nests on the ground, have the instinct of pairing; but they differ from such as build on trees in this respect, that after the female is impregnated, she completes her task without needing any help from the male. Retiring from him, she chooses a safe spot for her nest, where she can find plenty of worms and grass-seed at hand; and her young, as soon as hatched, take foot, and seek food for themselves. The only remaining duty incumbent on the dam is, to lead them to proper places for food, and to call them together when danger impends. Some males, provoked at the desertion of their mates, break the eggs if they stumble on them. Eider-ducks pair like other birds that place their nests on the ground; and the female finishes her nest with down plucked from her own breast. If the nest be destroyed for the down, which is remarkably warm and elastic, she makes another nest as before. If she be robbed a second time, she makes a third nest; but the male furnishes the down.
Pairing birds, excepting those of prey, flock together in February, in order to choose their mates. They soon disperse, and are not seen afterwards except in pairs.
Pairing is unknown to quadrupeds that feed on grass. To such it would be useless, as the female gives suck to her young whilst she herself is feeding. If M. Buffon deserves credit, the roe-deer form an exception. They pair, though they feed upon grass, and have but one litter in a year.
Beasts of prey, such as lions, tigers, wolves, pair not. The female is left to shift for herself and her young, which is a laborious task, and often so unsuccessful as to shorten the life of many of them. Pairing is essential to birds of prey, because incubation leaves the female no sufficient time to hunt for food. Pairing is not necessary to beasts of prey, because their young can bear a long fast; and we may add another reason, viz. that they would multiply so fast by pairing as to prove troublesome neighbours to the human race. Amongst animals that pair not, males fight desperately about a female. Such a battle amongst horned cattle is finely described by Lucretius. Nor is it unusual for seven or eight lions to wage bloody war for a single female.
The same reason that makes pairing necessary for gregarious birds obtains with respect to gregarious quadrupeds, those especially who store up food for winter, and during that season live in common. Discord amongst such would be attended with worse consequences than even amongst lions and bulls, who are not confined to one place. The beavers, with respect to pairing, resemble birds that place their nests upon the ground. As soon as the young are produced, the males abandon their stock of food to their mates, and live at large, but return frequently to visit them whilst they are suckling their young.