DIET. 679 



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 with 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 

 Prsecoces. 



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 prey and 

 some others, the moult is in mid-winter. The process is comparable 

 to the casting of scales in Reptiles, and to 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 

 unable to fly. There are many birds that moult, more or less com- 

 pletely, more than once a year; thus the garden warbler sheds its 

 feathers twice. The males of many birds assume special decorations 

 after a partial or complete moult before the time of pairing (ruff, knot, 

 golden plover). The ptarmigan changes its dress three times in the 

 year; after the breeding season the plumage becomes grey; as the 

 winter sets in it grows white, and suited to the surrounding snow ; in 

 the spring, the season of courtship, the mottled brown wedding robes 

 are put on. 



Diet. The food of birds varies greatly, not only in different kinds, 

 but also at different seasons. Many are herbivorous, feeding on the 

 soft green parts of plants, and in these birds the intestine is long. 

 Some confine themselves to grain, and these have large crops and strong 

 grinding gizzards, while those which combine cereals and insects have 

 in most cases no crop. A few sip honey, and may even help in the 

 cross-fertilisation of flowers ; those that feed on fruits play an important 

 part in the dissemination of seeds ; those that devour insects are of 

 great service to man. In fruit-eating and insectivorous birds the crop 

 is usually small, and the gizzard only slightly muscular. But many 

 birds feed on worms, molluscs, fishes, and small mammals ; in these 

 the glandular part of the stomach is more developed than the muscular 

 part. The nature of the stomach in the Shetland gull changes twice 



