34 BEHAVIOR OF PIGEONS. 



showed no such instinct, in at least one instance, though they might have done so had 

 they not been ready to lay immediately, i.e., without any interruption in incubation. 



On March 5, between 3 and 5 p. m., one of these doves laid an egg. The supposed 

 male had possession of it when found, and the other (supposed female) sat on the nest 

 close beside. Is the supposed male a female? And have we thus another pair of females, 

 mating, nesting, copulating, and incubating, as if male and female? The two doves are 

 devoted to each other, and their behavior is that of male and female. The supposed male 

 acts as a male, except that he crows very little and does not have the full sonorous voice 

 of the known males. Which dove laid the egg I am as yet unable to say. On Mar. 7, a 

 second egg was laid at 7 h 10 m a. m. Both doves are females. Their age at the time of the 

 second egg was 6 months and 20 days. (R19, C 7/17.) 



In continuing Professor Whitman's work, Dr. Riddle has studied with some 

 detail this pairing phenomenon between two females and has given the following 

 summary account of his observations: 



The continued isolation of two female doves is usually sufficient to induce their mating 

 with each other. Many of the phenomena of a normal pairing will be exhibited by such 

 unnatural pairs. Copulation, nest-building, egg-laying, incubation, and feeding of young, 

 all follow in the usual order. In working with hybrids between T. orientalis and St. alba 

 sex-controlled material produced by Professor Whitman I have been able to carry con- 

 siderably further the analysis of this conduct, obtaining the following significant results : 



(1) One or both members of a pair of females may function as the male in copulation, 

 and one may so function much more frequently than the other. 



(2) The amount of this predominance in mounting is dependent upon the relative 

 masculinity of the females of the pair. 



(3) A bird predominantly masculine in one mating will show predominantly feminine 

 behavior in another mating with an exceedingly masculine female. 



(4) This relative masculinity rests upon a physi'cal and physiological basis imposed 

 upon these birds by the conditions which affect their own sex-determination. 



The several features involved in the sex-control are treated elsewhere (see Volume II 

 of these works). A complete account, by the present writer, of the relative masculinity 

 and femininity of female and male birds respectively will appear in a volume now in course 

 of preparation. 



In our more recent studies of the detailed behavior of the members of pairs of the same 

 sex, some data have accumulated which touch the question of the relation which "energy" 

 and "aggressiveness" bear to sex. 



In the main, Professor Whitman's conclusion that the male is the more energetic and 

 aggressive finds confirmation here; furthermore, the more "aggressive" females studied 

 in the new lines of work have proved, in most cases, to be the more masculine in their 

 sex behavior; i.e., they have more often taken the part of the male in copulation. There 

 seem, however, to be some instances where this simple rule does not hold. Certainly there 

 are cases where the "larger" bird is not the more masculine; likewise, more "eager" birds 

 which are not more masculine. The exceptions to the above rule, though possibly of impor- 

 tance, can be treated adequately only in connection with our own forthcoming work. 



One may ask, How completely will the more masculine of a pair of females assume 

 the duties and behavior of a male? In reply it can be said, first of all, that both try to be 

 females; and that it is chiefly where two simultaneous feminine behaviors are precluded 

 by the nature of the activity, as in billing or copulating, that the testing struggle comes. 



If two such females differentiate themselves in the matter of "display" I have not 

 noted it; though I have not definitely, consistently, or preparedly looked for it. The more 



