208 ANIMAL FORMS 



The eggs of birds are relatively large, and are often 

 delicately colored. In some species the blotches and streaks 

 of different shades are probably protective, as in the plovers 

 and sandpipers, whose eggs blend perfectly with their sur- 

 roundings, but many other cases exist not subject to such 

 an explanation. 



The young require a high degree of heat for their devel- 

 opment, and this is usually supplied by the parent. In a 

 very general way the length of sitting, or incubation, is 

 proportional to the size of the egg, being from eleven to 

 fourteen days in the smaller species, to seven or eight weeks 

 in the ostriches. Before hatching, a sharp spine develops 

 on the beak, and with this the young bird breaks its way 

 through the shell. Among the quails, pheasants, plovers, 

 and many other species, the young are born with a covering 

 of feathers, wide-open eyes, and the ability to follow their 

 parents or to make their own way in the world. Such 

 nestlings are said to be precocial, in distinction to the alincal 

 young of the more highly specialized species, such as the 

 sparrows, woodpeckers, doves, birds of prey, and their allies, 

 which are born helpless and depend for a considerable time 

 on the parents for support. 



Some of the owls, crows, woodpeckers, sparrows, quails, 

 etc., remain in the same localities where they are bred. 

 They are resident birds. Most kinds of birds, at the ap- 

 proach of winter, migrate toward the southern warmer 

 climes, some species traveling in great flocks, by day or 

 night, and often at immense heights. In some cases this 

 movement appears to be directly related to the food-supply ; 

 but there are many apparent exceptions to such a theory, 

 and it is possible that many birds migrate for other reasons. 

 Certain species migrate thousands of miles, along fairly 

 definite routes, the young, sometimes at least, guided by 

 the parents, which in turn appear to remember certain 

 landmarks observed the year before. Sea-birds, in their 

 journeys northward or southward, keep alongshore, occa- 



