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 
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 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. 
Sh 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 toman. 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 
