1 68 Wild Birds 



only parts of one may get a shell in due course, thus producing 

 the "runts" occasionally seen in nests. Indeed, I have known 

 in the common hen a single instance in which a small and im- 

 perfect egg with a shell was incased in the yolk of a large and 

 normal egg, so that the curious anomaly of egg within egg was 

 produced in a most striking manner. In such rare cases the 

 small egg, though possessing a shell, is imperfect. 



Spots of pigment, when present, are often blurred, or, as in 

 the Orioles and Blackbirds, drawn as with a fine pen around the 

 shell, clearly showing, if other proof were lacking, that the egg 

 not only rotates on its long axis, but often oscillates in the 

 downward course in the ovarian tube. 



The delicately colored eggs of many wild birds are among 

 the most beautiful objects in nature, but what this wonderful 

 display of color really means is doubtful. The pale greenish- 

 blue, brown-mottled eggs in the open nest of the Song Sparrow 

 seem to be protectively colored, because they match their sur- 

 roundings so perfectly, yet the Crow also lays mottled eggs, and 

 the European Magpie, which produces eggs of the same pattern, 

 effectively conceals them by building an arched roof over its 

 nest, which is entered at the side. 



A long time ago it was observed that the eggs of many birds 

 which are laid in dark holes are often white, as in Parrots, Wood- 

 peckers, Kingfishers, and Swifts. It was only natural to sup- 

 pose that the lack of pigment might be due to the absence of 

 light, and further that it was a useful adaptation, since the 

 whiter and more conspicuous the egg the more likely was it to 

 escape injury from the owners when entering their dimly lighted 

 apartments. Here also many exceptions occur, which may be 

 due to the fact that the color of the egg is a more stable character 

 than the nesting habit. 



As in all other animals, the relative size of the egg is directly 

 proportional to the degree of development attained by the 

 young at birth, the altricial Robin or Cedar-bird laying a rela- 

 tively smaller egg than the praecocial Snipe or Grouse, which is 

 able to run about from birth or as soon as dried off. 



The eggs are usually laid on successive days, and in definite 



