THE BROODING INSTINCT IN THE DOMESTIC FOWL 287 



the brooding instinct, and the physiological state of the bird. 

 In this connection it may be noted that it frequently happens 

 that a bird will exhibit periods of rest in egg production, which 

 are as long continued as those of broodiness, and yet show none 

 of the objective features of broodiness whatsoever. Such cases 

 prove that the cessation of ovarian activity (laying) is not alone 

 capable of causing the onset of broodiness. It would be extremely 

 interesting to have more extensive data as to energy consump- 

 tion in these birds which are not laying, and yet are not 

 manifesting the broodiness instinct. 



In the fowl, broodiness seems to be distinctly a female secondary 

 sexual character. This, of course, is not true in some other 

 species of birds where the male bird alternates with the female 

 in brooding eggs. Ordinarily in the domestic fowl the cock 

 takes no part whatever in the brooding of the eggs or the chicks. 

 It has, however, long been the practice with practical poultry 

 keepers in certain parts of the world to use the castrated cock 

 or capon for the purpose of brooding chickens. I know of no 

 record of capons being used to incubate eggs. The brooding 

 behavior of the capon needs, and will certainly repay, careful 

 study by a trained behaviorist. 



SUMMARY 



This paper presents data regarding variations in the manifes- 

 tations of the brooding instinct in fowls. It is shown that: 



1. Broodiness normally constitutes one element in the cyclical 

 reproductive activities of the female. It recurs with greater or 

 less regularity following periods of laying. 



2. The degree of intensity of the brooding instinct, both in 

 respect of its objective manifestations and in respect of its 

 physiological basis, may vary considerably at different times in 

 the life of the same individual. 



3. Broodiness in the domestic fowl is not necessarily connected 

 with any particular season. It may occur entirely outside the 

 regular breeding season. 



4. While ordinarily broodiness is preceded by the laying of 

 a " clutch " of eggs, this need not necessarily be so. Cases are 

 cited in which well marked broodiness occurs without ante- 

 cedent laying. 



