A STUDY OF THE INCUBATION 

 PERIODS OF BIRDS 



What controls the length of incubation with birds? It 

 is the purpose of this study to find, if possible, a correct 

 answer to this question. 



Introduction 



The processes going on within an egg during incubation 

 are of fundamental and paramount importance to the species 

 and race, in no way less than the process of fertilization; 

 fertilization and incubation are co-equal and interdependent, 

 and through them the time space between generations is 

 bridged and the race perpetuated. Fertilization is governed 

 by definite limitations and conditions. Does it seem reason- 

 able to believe that the length of the equally important 

 period of time necessary to complete the marvelous steps of 

 development following fertilization is a matter of chance, 

 a "hit or miss" duration? 



It is inconceivable that such can be true ; one arises from 

 a study of the embryology of the "chick" in amazement that 

 the wonderful and complex changes in an egg from a single 

 cell to a peeping chicken can be brought about in a brief 

 three weeks. Such perfection of detail, with all its potential 

 specific and racial conditions unfolded, must surely require 

 a fixed and definite period of time for its completion. Does 

 it not seem more reasonable that this period of time must 

 be relatively fixed for each species, and be controlled by 

 factors or conditions which collectively might be called a 

 law? 



I believe that a knowledge of such factors, or such a 

 law, is not merely academic, but, on the contrary, is of de- 

 cided importance, and constitutes a block to be fitted in the 

 mosaic being slowly put together by ornithologists, each in 

 his day. Moreover, the writer has discovered, through his 

 study of the question, that it is fraught with fascinating 

 interest, and, too, opens up unexpected and wide fields for 

 original research. 



The Problem 



The problem in hand is to answer the question, Why 

 does a house finch's egg take fourteen days to hatch, an 

 ostrich's forty-two days, an emu's fifty-six days, or a hum- 

 mingbird's fourteen days? It is the work of this study to 

 analyze the published data concerning incubation periods, 

 and to examine the explanations heretofore given, as to 

 what governs the length of incubation, and to determine if 



