162 CHILDHOOD OF ANIMALS 



on the edge of the nest for their young. The adult gull on Plate VIII 

 was drawn in the attitude assumed just before she throws up food 

 for the young. Petrels secrete a kind of oil from the fish on which 

 they live, and discharge it by their beaks into the mouths of their 

 young. Little cormorants thrust their bills down the short straight 

 throat of their mothers and help themselves from her stomach ; 

 whilst young pel cans take fish from the mother's enormous pouch- 

 like bill. Young pigeons obtain their food by thrusting their 

 beaks into the mouth of the mother and absorbing the so-called 

 pigeons' milk, which is partly digested food and partly a secretion 

 from the crop. Whatever method be adopted, the feeding of the 

 young may go on until these are nearly as large as the parents. 



Young birds, especially those that are born naked, are extremely 

 sensitive to cold, their temperature rising and falling with that of 

 the surrounding air, just as happens with reptiles, and no small 

 part of the duty of the parents is to keep them warm. This is 

 generally the work of the mother, and for some days, in the case of 

 the smaller singing birds, she hardly leaves the nest, the male 

 during this time doing all the work of foraging. In four or five 

 days the little birds have found their feet and are able to move 

 about in the nest, and then the mother is able to leave them for a 

 longer interval, and to take up her share of collecting food. 



And so in nearly all birds, from the choice of the place for the 

 eggs, through the long duty of incubation, and for a longer or shorter 

 period after the young are hatched, one or both of the parents 

 are fully occupied with parental duties. The final period of brood- 

 care lasts for periods varying from three weeks to several months. 

 Then suddenly it comes to an end. The parents resume their 

 natural devotion to their own personal wants, and even those that 

 have been most assiduous and most devoted now quite suddenly 

 either fly off to new haunts, leaving their offspring behind, or drive 

 the fledglings away from them. The abandoned young often 

 consort until they have reached sexual maturity, when new instincts 

 awaken and the battles for mates begin. 



If the time occupied in building the nest, in incubation and in 

 looking after the young be added, and if it be remembered that 

 most birds breed at least once a year, and those which get over 

 their duties quickly often breed twice a year, we reach the conclusion 

 that a large part of the time of adult birds is occupied with parental 

 care. This increased care has made it possible for the number in 

 the family to be very greatly diminished. 



