EGGS OF BIRDS 76 1 



reasons why the number of offspring decreases as animals become more 

 highly evolved. 



The size of the egg usually bears some relation to the size of the bird. 

 Of European birds, the swans have the largest eggs, the golden-crested 

 wrens the smallest. It is said that the egg of the extinct Moa some- 

 times measured 9 in. in breadth and 12 in. in length ; while that of 

 the extinct ^pyornis held over two gallons, some six times as much 

 as an ostrich's egg, or a hundred and fifty times as much as a fowl's. 

 Yet the size of the egg is only generally proportional to that of the 

 bird ; for, while the cuckoo is much larger than the lark, the eggs 

 of the two are about the same size ; and while the guillemot and the 

 raven are almost of equal size, the eggs of the former are in volume 

 about ten times larger than those of the latter. The eggs of birds 

 whose young are rapidly hatched and soon leave the nests are large. 

 Professor Newton remarks that " the number of eggs to be covered at 

 one time seems also to have some relation to their size," while from 

 what one notices in the poultry-yard, and from a comparison of the 

 habits of different birds, it seems probable that a highly nutritive, 

 sluggish bird will have larger eggs than a bird of more active habit and 

 sparser diet. 



The shell of the egg is often ver^^ beautifully coloured ; there is a 

 predominant tint upon which are spots, streaks, and blotches of varied 

 colour and disposition, so that the egg is almost always characteristic of 

 the species. Pigments related to those of the blood and the bile are 

 deposited while the shell is being formed in the lower part of the 

 oviduct.. As the eggs may move before the pigments are fixed, blotch- 

 ings and markings naturally result. The coloration is often protectively 

 harmonious with that of the surroundings. Thus eggs laid almost on 

 the ground are often brownish like the soil, those laid near the seashore 

 often look very like stones, while conspicuous eggs are usually found 

 in covered nests. 



Some newly hatched young are naked, blind, and helpless, and have 

 to be carefully fed by their parents until they are fully fledged. This 

 is true of the thrush and of many other song-birds. Others are born 

 covered wnth down, but still helpless ; while a few, like the chicks, 

 are able to run about and feed themselves a few hours after they leave 

 the egg. Those which require to be fed and brooded over are called 

 Altrices ; those which are at once able to feed themselves are called 

 Preecoces. 



Moulting. — Every year birds lose their old feathers. This 

 moulting generally takes place after the fatigue of the breeding season, 

 but in the case of the swallows, and the diurnal birds of pre}- and some 

 others, the moult is in mid-winter. The process is contrasted with 

 the casting of the dead outermost lay.r of ths epidermis in Reptiles; 

 it is nearer the shedding of hair in Mammals. Feathers are so easily 

 injured that the advantage of the annual renewal is evident, especially 

 when it takes place just before the time at which it may be necessary 

 to set forth on a long migratory flight. 



In moulting, the feathers fall out and are replaced gradually, but 

 sometimes they are shed so rapidly that the bird is left very bare ; thus 

 moulting geese, ducks, and rails lose all their quills at once and are 



