BIRDS IN THEIR NESTS 227 



less, and they are often devoured by the parent bird 

 instead of being carried away. The digestion of very 

 young birds must be feeble, and doubtless much of the 

 food given them passes undigested through the aliment- 

 ary canal, so that it is capable of affording nourishment 

 to the parents. Birds are nothing if not economical. 



Of course, all birds are not so careful of the sanitation 

 of the nest. Every one knows what a filthy spectacle a 

 heronry is. According to Mr. Herrick, the instinct of 

 inspecting and cleaning the nest is mainly confined to 

 the great passerine and picarian orders. It is obviously 

 not necessary in the case of those birds, such as fowls, 

 of which the young are able to run about when born ; 

 nor is it needful in the case of birds of prey, who take 

 no pains to conceal the whereabouts of the nest. Young 

 raptores eject their semi-fluid excreta over the edge of 

 the nursery ; thus the nest is kept clean, but the drop- 

 pings on the ground betray its presence to all the world. 



Coming now to our other question : How do young 

 birds obtain the water which they require ? we have no 

 help from Mr. Herrick. He makes no mention of this 

 in his most interesting book. It is possible that nest- 

 lings are not given anything to drink, that the juicy, 

 succulent insects or fruits with which they are supplied 

 contain sufficient moisture for their requirements. We 

 must remember that the skin of birds is very different 

 from that of man. It contains no sweat glands, so that 

 a bird, like a dog, can only perspire through its mouth. 



The breath of mammals is so surcharged with mois- 

 ture that when it is suddenly cooled the water vapour 

 in it condenses ; the result is we can " see the breath " 



