162 THE BIOLOGY OF THE SEASONS 



of the doorway. The last instance suggests the case of the 

 hornbills, whose remarkable story has been so well told by 

 Mr. Pycraft and others. The female is weakly and moulting 

 at the breeding-time, and the male shuts her into a hole in 

 a tree-stem. The floor may have to be deepened, or it may 

 have to be raised with dry earth from the termitaries. The 

 doorway is built up, too, so that intruders are readily kept 

 out, while the hole is large enough to let the male bird's bill 

 in. It is on him that the labour devolves of finding food 

 for his mate, and afterwards for his family as well. He is 

 often worn thin with his other-regarding exertions, while 

 the female bird becomes fat. Sometimes, the story runs, 

 the male bird dies without having the reward of even seeing 

 his children. 



Cases, like that of the hornbill, where there is some 

 building as an accessory to the nest, point the way to 

 definitely built nests, such as those of the swallow and the 

 house-martin. The swallow's is the more primitive of the 

 two it is made of mud strengthened with pieces of straw ; 

 it is like " half a deep dish," open at the top ; it is built 

 against a rafter or a chimney ; it has a lining of small 

 feathers and soft grass. The house-martin's is also made of 

 mud, strengthened with pieces of straw or hair ; it is built 

 against the wall of a house or against a cliff ; it is like a 

 bowl in shape, with its open side against the surface selected, 

 and with a small entrance near the top ; there is a lining 

 of feathers, which the martin catches in the air, and pieces 

 of straw. It is difficult to understand how the bowl hangs 

 on to a smooth surface even to a vertical pane of glass ; 

 it is interesting to watch the patient carefulness of the 

 builders, adding about half an inch every morning and no 

 more till next day, so that it hardens well, the whole edifice 

 taking about a fortnight. 



A masterpiece along the line illustrated by swallow and 



