230 ELEMENTS OF OEJTITHOLOGT. 



altogether, by laying in the nests of other Birds, a practice 

 facilitated by the small size of their eggs. 



One brood annually is the rule with Birds, though many hatch 

 two or even three broods in the year. 



Parent birds sometimes assist their unhatched brood to break 

 the shell when they hear the cry of the young one within it. 



The only Birds which neither incubate their eggs themselves 

 nor provide them with foster mothers, are the mound-building 

 birds of the Australian region, such as Megapodius. They raise, 

 as before said *, large heaps of vegetable substances — refuse of 

 all kind — and earth, and therein deposit their eggs, which are 

 hatched by the heat produced through such an accumulation of 

 decaying and slightly fermenting matter. Their eggs are large, 

 and the young developed in them are so fully formed when 

 hatched, that they can not only force their way to the surface of 

 the mound, but having reached it can fly away at once for short 

 distances. 



Some species lay their eggs in the loose hot sand of the 

 beach (above high water-mark), where the rays of the sun 

 suffice to hatch them. 



Birds differ much as to, the state of development in which 

 they are hatched. Many are born nearly naked and helpless, 

 and require good shelter till they acquire feathers, as is the 

 case, e. g., in the Canary and the Sparrow. Others, like the 

 Heron, are born nearly naked, and acquire a downy covering 

 before they acquire feathers. Others again, like the Hawks, are 

 born helpless but covered with down ; while yet others, like the 

 Chicken, are hatched covered with down, and can run about at 

 once. Birds of the latter kind are said to be precocious. The 

 most precocious of all are the Mound-builders above mentioned. 



Toung birds are assiduously fed by their parents, and the 

 crops of Pigeons secrete a nutritious fluid which the young 

 partake of, extending their heads down the gullet of one or 

 other parent for the purpose. 



The relations of the colours of the plumage of the young and 

 the adults of both sexes, and the process of moulting, have been 

 already noted t- 



JVidi/ication. — ^As country boys know, the shapes of, and the 

 materials used in making, the nests of Birds are difierent in 

 different species. Some make carefully made covered nests, 



* See atite, p. 9, t See ante, p. 140. 



