298 THE BIOLOGY OF BIRDS 



materials mixed with salivary juice, so that would-be 

 intruders are readily baffled. On the male falls the responsi- 

 bility of providing food for his imprisoned mate, and by-and- 

 by for the single nestling as well. He brings food-materials 

 — fruits and seeds and insects, often enclosed in a thin skin 

 like that of a sausage, which turns out to be a product of the 

 lining of the gizzard from which the food is regurgitated. 

 The female bird becomes fat, but the male sometimes dies of 

 exhaustion, especially in bad weather. 



Platform Nests, — From nests or apologies for nests on 

 the ground, one might pass to the earth-mounds made by 

 flamingos, or in another direction to rough platform nests 

 like that of the wood-pigeon, which is often so slight that the 

 white eggs may be seen from below. From a rough stick 

 platform there is a gradation leading to the more elaborate 

 constructions made by rooks and crows. Improvements on 

 this are seen in the fence of thorny sticks which magpies 

 build and in the sparse internal bedding gathered by bittern 

 and heron. 



Nests of Earth. — Deserving a place by themselves are 

 the solidly built nests, such as the swallow's — generally like 

 half a saucer, built of mud mixed with short straws, and made 

 comfortable inside with a lining of feathers and fine grasses. 

 An improvement on this is made by the house-martin, for 

 the mud nest is shaped like half of a deep cup and is closed 

 in except the doorway at the top or corner of one side. 

 There is a lining of feathers, which the martin catches in the 

 air, and pieces of straw. The nest of the South American 

 oven-bird (Furnarius) is nearly as big as a football and weighs 

 8-9 pounds ; it is made of mud mixed with a few sticks and 

 straws, and shows an elaboration in being divided into two 

 rooms, an ante-room and an egg-room. It is a big, massive 

 nest, but it is built pellet by pellet by a bird with a tiny bill. 



Extraordinary Nests, — Some of the Passerine birds use 

 their saliva to moisten or glue the fibres or tiny twigs with 

 which they build their nest, and this habit points on to the 

 extraordinary nest of the sea-swift Collocalia of the Far East 

 which is made of consolidated salivary juice. The nest is 



