242 Bird - Lore 



here that, with the building of a conspicuous nest, it no longer availed the bird 

 to lay a protectively colored egg, for whatever concealed the nest would like- 

 wise conceal the eggs. It is a fact in nature that a structure exists only so long 

 as there is absolute need for it, and that as soon as the need passes, the struc- 

 ture gradually degenerates, though it usually persists through a great many 

 generations. Examples of this are the tonsils and appendix of man which un- 

 doubtedly at one time played a very important part in our metabolism but 

 which have long since ceased to function and are in the process of degeneration. 

 So, in the coloration of birds' eggs, while the pigment was originally developed 

 as a protective measure before the birds built elaborate nests, the need for those 

 colors has gradually passed away with the higher types of birds that build 

 conspicuous nests, and the colors are in the process of degeneration. The 

 degeneration has progressed more rapidly with some species than with others 

 and has resulted in the great variety of ground-colors and markings that we 

 find today, most of which must be considered conspicuous. The rate of degene- 

 ration is remarkably uniform with most species, however, and so we find today 

 that each species lays a characteristic egg and each family has a type of egg 

 from which there is little departure. Thus, all Robins lay plain blue eggs and 

 so do most of the Thrush family. Spotted Sandpipers lay brownish eggs spotted 

 with black and so do most of the shore-birds; Crows lay greenish eggs spotted 

 with black and so do the Jays; Orioles lay bluish white eggs streaked with black 

 and so do most of the Blackbirds; Warblers lay whitish eggs spotted with 

 brown; Vireos, white eggs with just a few black specks, and so on. Occasionally 

 one finds a nest in which the eggs show a great deal of variation, as that of the 

 Song Sparrow, here illustrated, or that of the Swamp Sparrow in which the 

 eggs are plain blue instead of heavily spotted, but these variations probably 

 mean but little except perhaps to give added weight to the belief that the 

 colors are in the process of degeneration. 



Another fact that has perhaps hastened the change from a protectively 

 colored to a conspicuous egg is the fact that a conspicuous egg today often 

 benefits the species. It is a well-known fact that most birds do not begin in- 

 cubating until the laying of the last egg, and that in the meantime the eggs lie 

 exposed to all of the enemies living in the vicinity. It might be thought, there- 

 fore, that a protectively colored egg would be beneficial. On the contrary, if 

 the bird has selected a nesting-site where some enemy is likely to find the 

 nest sooner or later, or if the nest has not been properly concealed, it is far 

 better that it should be found at this stage than later, ,as there would be less 

 delay in building a new nest and laying more eggs. Nature provides that the 

 bird has very little attachment for its nest during the period of egg-laying, and 

 practically all birds desert it upon the least provocation. Too close approach, 

 the disarrangement of a single leaf or anything that suggests to the bird that 

 its nest has been discovered before incubation has begun is usually sufl&cient 

 to cause it to desert the nest and start again somewhere else. After incubation 



