220 WALLACE CRAIG 



may be, as Professor Whitman observed, only a half hour until 

 the birds are at work preparing for another laying. 



When wild birds (and other animals) kept in 'captivity refuse 

 to breed, the trouble in many cases is surely psychological. It 

 is not that the birds are in poor health, or have improper food, 

 etc. It is that the conditions fail to stimulate or even positively 

 inhibit the arousal of their breeding instincts and of the asso- 

 ciations formed during their wild breeding experience. 



Between the different species and different orders of birds 

 there are great differences in the relation of ovulation to en- 

 vironmental conditions. The stimulation of ovulation by the 

 social activity of the male occurs no doubt in all the Colum- 

 bidae and probably in a great many other monogamous birds. 

 The domestic fowl and perhaps all the Phasianidae (Craig, 

 1911; Harper, 1904, p. 353) present an extreme contrast to 

 the pigeons, in that their ovulation is highly independent of 

 mating. Parasitic layers such as the European Cuckoo and 

 the North American Cowbird (Molothrus ater Bodd) are probably 

 descended from forms whose ovulation resembles that of the 

 pigeon, but have evolved to a state in which ovulation is more 

 independent of environment, at least not depending upon any 

 stimulus of the bird's own nesting activity. This is in agree- 

 ment with the conclusion of Herrick (1910, p. 232) that the 

 habit of parasitic laying is connected with a disturbance of the 

 "attunement of egg-laying to nest-building." 



Harper (1904, p. 352) hinted that what we* have said of pigeons 

 does not apply at all to the Mammalia, that in the latter ovula- 

 tion is "exclusively a female function." But this is an error. 

 It has been shown for many Mammals (Thomson, 1839, p. 44*; 

 Marshall, 1910, pp. 134-139; Longley, 1910) that ovulation is 

 favored by or may even depend upon union with a male. And 

 there is reason to believe that what is true of pigeons is true 

 also of these mammals: that in so far as ovulation is depen- 

 dent upon environment, it is dependent, not upon any one 

 afferent stimulus, but upon the entire situation — involving the 

 female's inborn disposition, her whole past history (see pp. 

 215-218) and all factors in the present environment which 

 affect the social, emotional situation. 



