300 



THE REASON WHY : 



&quot; When unobserved 



Pluck from the barn a straw, till soft and -warm, 

 Clean and complete their habitation grows. THOMSON. 



it must be thickly lined with non conductors of heat. All tbesa 

 conditions are fulfilled with the skill of a natural philosopher. 



963. The nests of the larger class of birds of hardier nature are of rude con 

 struction ; but those of the smaller species display, in a remarkable manner, the 



qualities here indicated. The parents 

 of the coming offspring, father and 

 mother, co-operate in the construction 

 of the nest, for the external part c-1 

 which straw and twigs are collecteo., 

 and woven into a sort of basket-work. 

 This not possessing the requisite 

 durability, and allowing, moreover, 

 the air to penetrate, and the heat to 

 escape, a quantity of fine clay is 

 collected with considerable labour, and 

 worited into a sort of mastic by moans 

 of a viscous fluid secreted by glands 

 placed under the tongue of the bird. 

 With this mastic, the parents plaster 

 the interior of the nest, carefully stopping up every crevice and air-hole. The floor 

 of the nest, however, formed by such plaster is necessarily hard, and would injure 

 the yo&quot;ti(rlings by its pressure. The parents, therefore, fabricate a carpet, which 

 they spread upon the floor of the nest, over which they place a soft mattress, the 

 materials of which consist of wool and hairs taken from the backs of animals and 

 the cottony parts of certain plants. The countless journeys and fatiguing labour 

 necessary to accumulate hair by hair, and filament by filament, may be easily 

 conceived. Sometimes the bird strips its own breast of natural down to form 

 a bed for its young. Thus the eider duck provides for the comfort of its 

 offspring, by taking from its own body part of that down which is sought for and 

 collected at such a cost for the pillow of luxury. 



964. Why do some birds frequently vary the materials of 

 iheir nests ? 



This is doubtlessly done for the purpose of assimilating the 

 nest in appearance to surrounding objects, so as to accommodate 

 their habitation &quot;to existing circumstances, anu to secure it 

 from observation. 



965. Why do some birds maJce their nests warmer than 

 the nests of other birds ? 



Because the first-mentioned are those which are necessarily 



