THE EGGS OF BIRDS 



BY ELSA G. ALLEN 



ONE cannot find among the multitude of wonders in 

 nature anything more marvelous than the develop- 

 ment of an egg. Whether it be a butterfly which 

 flourishes for a day only to die after depositing its eggs, 

 or a reptile which lazily leaves its eggs with only the 

 warm sand to mother them, or a fish, like the salmon, 

 which, with incredible strength, jumps the rapids to 

 spawn in the upper reaches of rivers, or most appealing 

 of all, a bird which builds a beautiful nest for its treas- 

 ures, the egg in every case is structurally the same, and 

 the miracle of life unfolds according to the same laws 

 of cell division. 

 A single cell 

 marks the be- 

 ginn i ng of 

 every organ- 

 ism. It divides 

 into two cells, 

 then four cells, 

 and so on 

 through the 

 most intricate 

 specia'.izat i o n 

 of groups of 

 cells. At last 

 the perfected 

 embryo, having 

 used up the 

 mass of food 

 stored within 

 the egg, must 

 hatch and seek 

 its livelihood in 

 the great world 

 where a thou- 

 sand dangers 

 beset it. For it 

 is the most re- 

 lentless law of 

 nature that everything must struggle for existence, but 

 another law provides that those forms which are sub- 

 ject to the most dangers produce the greatest number of 

 offspring. Thus the progeny of many insects must num- 

 ber trillions that some may survive the birds which con- 

 sume them by countless thousands. The cod risks its 

 spawn to the open sea and must therefore produce mil- 

 lions of eggs that enough may survive to continue the 

 species. The reptiles lay comparatively few eggs but 

 likewise give them no protection, leaving them to be 

 hatched by the heat of the sun or decaying vegetation. 

 But in the realm of birds parental care for the eggs 

 reaches its highest development. 



For as birds evolved from reptile-like ancestors and 

 developed a constant body temperature, so their eggs, 



Photograph by A. A. Allen. 



NEST AND EGGS OF THE BLACKBURNIAN WARBLER 

 Birds which do not lay protectively colored eggs conceal them in well-hidden nests 



in order to develop, had to be kept continually warm. 

 Because of this, nearly all birds, except the mound birds 

 of Australia and the brush turkeys of New Guinea, in- 

 cubate their eggs and herein lies the most fundamental 

 difference between the eggs of birds and those of their 

 ancient progenitors, the reptiles. 



But while the eggs of reptiles with their white leathery 

 shells are by no means beautiful, the eggs of birds are 

 among the loveliest things in nature, and they have al- 

 ways held a great fascination for man. From the tiny 

 hummingbird's egg, no longer than a bean, to the giant 



ostrich egg, 

 which is be- 

 tween five and 

 six inches in 

 diameter, there 

 is every grada- 

 tioninsize. But 

 the size of the 

 egg does not 

 depend entire- 

 ly upon the size 

 of the bird 

 which lays it. 

 For example, 

 the catbird and 

 spotted sand: 

 piper are prac- 

 tically of the 

 same size but 

 the sandpiper's 

 egg is consid- 

 erably larger. 

 The reason is 

 not difficult to 

 find, for the 

 young catbird 

 upon hatching 

 is still but 

 poorly developed, tiny, helpless, featherless, homely to 

 a pitiful degree, while the young sandpiper greets the 

 world covered with down and ready to chase flies with 

 its mother. 



In like manner the length of the incubation period 

 depends largely upon the stage of development reached 

 by the chick before hatching. Birds such as the catbird 

 and other perching species, which have altricial young 

 needing care in the nest for some time, do not incubate 

 their eggs as long as those like the shorebirds and ducks 

 which have precocial young. The eggs of most of our 

 common small birds require incubation for from ten 

 days to two weeks. Those of the fowl-like birds such 

 as the ruffed grouse about three weeks, those of the ducks 

 about four weeks, and the eggs of the emeu, a large 



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