The labour of feeding the young family is a heavy task in which both parents commonly share. There are no cases of unsuitable feeding of nestlings by careless or ignorant parents. A regular course of nursery dietary is practised, in particular with nidicolous species, where the young are born in a helpless condition; often a special infant food is prepared by a process of regurgitation, or food partly digested and thrown up. Thus baby finches are fed on food made of digested insects; parent parrots also prepare a digested vegetable food; storks break up worms and frogs and pieces of little fishes and mix it with partly digested matter and throw it out on the edge of the nest for the family meals. Young pigeons thrust their beaks into the mouths of their mothers to absorb the so-called pigeon’s-milk, which is really digested food mixed with a secretion from the crop; little cormorants thrust their bills right down the neck of their mother and help themselves to food out of her stomach. The petrels secrete oil from the fish they eat to feed the young: this oil is used also as a weapon of defence both by the parents and the nestlings, who squirt it out from their mouths and nostrils at any unwelcome intruder on the privacy of the nest.[39]
When the young are fed entirely on insects the work entailed on the parents is enormous. A pair of blue tit-mice, for example, have been seen to make no less than four hundred and seventy-five journeys to the nest during a day’s foraging extending over seventeen hours. Again, the male of the common dabchick works untiringly, and has been seen to take as many as forty journeys, with food, in the space of an hour, back to the nest, where his wife waits with the children, which commonly perch on her back and are protected by her wings. Small wonder is there that the labours of both parents are needed to keep the young families from starvation. In some cases a practical division of work is arranged; and the father will bring a different kind of food from the mother. With the stow-chat, for instance, the mother brings small prey, generally spiders, but sometimes butterflies and moths, while the father selects and carries large caterpillars. Even where the young are precocious, fairly active at birth, and soon able to feed themselves, one or both parents for a considerable time guard, teach and protect them. Great bravery and intelligence are displayed in the face of any danger, not only will many parent-birds savagely attack an enemy, but in some cases, as, for instance, the plover or the partridge, the mother will feign to have a broken limb or to be lame, to draw off from the young the attention of the intruder. No parental duty is neglected. Daily lessons are frequently given to the nurslings on the right kind of food and the best way of feeding. Thus young birds of prey are instructed, first in the art of breaking up their food, and later in the best methods of its capture. Young swallows, again, receive a carefully graduated course of lessons on the difficult work of catching the insects which form their food, while they are flying. The parents of the woodcock carry their children to the feeding ground, to and from the nest, supporting the precious little ones with their beaks, and pressed close within their feet, which are used as maternal arms.[40]
A delightful incident was witnessed during the feeding-time of a red-backed shrike—[41]
“The male had brought to the nest a young bird, and, pulling off its head, proceeded to ram it down the throat of a very unfortunate youngster. But the morsel was too big, and had to be readjusted, not once, but many times; and finally it was forced home with such success that the wretched bird was in imminent danger from choking. At this the female, who had been sitting on the opposite side of the nest, making, apparently, very sarcastic comments on the awkwardness of her lord, and males in general, suddenly seized the offending head and, dragging it forth, proceeded to tear it into small pieces, giving each of the brood a piece. And during this time the male looked on in what appeared to be a very subdued fashion.”
Almost all birds take great trouble to ensure the sanitation of the nursery, and are diligent in their care of the health of the young. All the excrements are removed from the nest, a task that is rendered easy, as the droppings of the young are enclosed in a white, film-like envelope or capsule. A most careful search is made at the bottom of the nest for these capsules by the parents whenever they come to feed the young. Do they fail to find the expected capsules, one or other of the parents after the feeding will tap, tap on the anus of the young birds as if to remind them of a duty neglected.[42] This is, perhaps, the most extraordinary example of parental care that I have been able to discover. One wonders how far this apparent recognition of the necessity of regular habits and cleanliness is instinctive, or how far we may grant to these parents some direct realisation of the dangers arising to their children from neglect and a dirty nursery.
It must not, however, be thought that all birds are good parents. In some species there would seem to have been a revolt against family ties and the duty of caring for the young. The common cuckoo and some other cuckoos are well-known examples. Among them, the mother, as every one knows, always lays the eggs in the nest of some other birds, and the young cuckoo, when it is hatched, would seem to have some knowledge of its precarious position as a stranger. It creeps under the nestlings of its foster-parents, and, by a violent effort, raises them one by one on its hollow back and jerks them out of the nest, so securing undivided attention in its alien nursery. A similar parasitic habit, not yet so firmly established, is found among the cow-birds of the Argentine. Mr. W. H. Hudson has seen the mothers trying to build nests and failing to do this, as if they were struggling to regain a dying instinct. The females flutter about the mud-nests of the oven-birds, and whenever a chance presents itself will dart in and lay their eggs. Other cow-birds make no effort at all in nest-building, and always lay their eggs in the occupied nests of other birds, and, as their eggs develop very quickly, the intruders hatch out before the true children of the nursery and rob them of their parents’ care.
What do we learn from this? That neglect on the part of the mother—any shuffling out of her duties, thereby placing the care of her children on the shoulders of other parents, leads to crime and disorder in the social organisation.
Some birds are content with very little care for home-building ready for their eggs. Birds belonging to many different species make nurseries in hollow trees, caves, burrows or natural cavities, sometimes lining them with leaves and feathers to make them soft, but sometimes even neglecting this care. The New Zealand kakapo or ground parrot, to take one instance, hides in any hole it finds and lays its eggs there without any preparation; the kingfisher, again, digs out a hole in the ground, or occupies one that it finds. Emus scrape a shallow hole in the ground and do not cover the eggs. The cassowary scrapes together a rude pile of leaves and mould on which she lays the eggs. Some of the megapodes or bush turkeys bury their eggs in the sand, and then take no further trouble about them, leaving incubation to the chance warmth of the sun. Others build enormous heaps of decaying leaves, forming a hot-bed from natural fermentation, by which the chicks are hatched out with no trouble to the parents. The young of the megapodes are the only living birds that are hatched out able to fly at once and ready to take care of themselves. It would appear that neglectful parents foster self-development in the children.[43]
Where the mother broods alone over the eggs it sometimes happens that the father-bird takes no interest in the family. The polygamous gallinaceous birds appear to be without, or to have lost, the paternal instinct. Peacocks, pheasants, turkey-cocks, and barn-door cocks do practically nothing for their families, and while the mother-birds’ care in feeding and guarding the young is untiring, the fathers are running after amorous adventures. The conduct of the male turkey is even worse, for, prompted by jealousy, he will often attempt to devour the eggs, and the young are protected from his attacks only by the mothers uniting together in troops. Here we see the exact opposite conduct in the two sexes from that in such a family as the sticklebacks, where good fathers replace bad mothers. But the same result follows. In either case the neglect of parental duty by one or other parent is a source of weakness to the family and increases the risks to which the young are exposed.[44]
I must insist on how strongly conduct is affected by the conditions of the home; and any change of habits will directly modify parental behaviour. Thus an animal habitually domestic may easily change under the pressure of external causes. Thus wild ducks, though good parents and strictly monogamous, and very highly developed in social qualities when in the wild state, become indifferent to their offspring and loosely polygamous under domestication.[45] Civilisation, in this case, depraves the birds as often it does men. But the examples of bad parents among birds are few in number.