REPRODUCTIVE CYCLE. 99 



of a different species are very apt to prefer a mating not with their own kind, 

 but with a member of the species among which they have been reared. The author's 

 phrase, "very apt to prefer," indicates that such means of social education are 

 not always efficacious, and this fact shows that some degree of innate preference 

 probably exists. Adult preferences must thus be regarded as the result of two 

 factors, instinct and experience. 



This fact that the range of stimuli to which an instinctive act is susceptible 

 may be modified by experiences previous to the first expression of the act develops 

 a novel and important principle of instinctive modification for the more prevalent 

 doctrine assumes that instincts become modified only through the influence of 

 simultaneous activities. 



It is possible that previous experience is efficacious in part by removing fear 

 and distrust or indifference and substituting therefor a more positive attitude of 

 familiarity. There are some facts which indicate a fear and distrust of unfamiliar 

 species. A pertinent example is described in Chapter XII. A young geopelia 

 reared under ring-doves was placed with a young dove of its own species at the age 

 of 7 weeks. It immediately manifested fear and terror. The second dove was 

 reared with gcopelias and found no cause for alarm in its new companion. Fear and 

 distrust tend to prevent matings, as is evident from the account of a pair consisting 

 of a mourning-dove and a white ring-dove (found in manuscript C 7/7). On the 

 other hand, there is evidence that the normal attitude of some species towards 

 members of some other different species is one of indifference. Under the topic 

 "The Disposition to Fight," in Chapter I, it is stated that the wood-pigeons and 

 white-faced pigeons, during the period of nesting, manifested hostility only towards 

 members of their own species. 



Behavior is the means of the selection or recognition of the sexes in mating. 

 A male desirous of mating makes advances to various birds, and the outcome is 

 determined by the response elicited. Continued hostility and indifference will 

 in time discourage the wooer, and the search is prosecuted elsewhere. A certain 

 type of response is essential to the mating. This preference for certain types and 

 modes of behavior in the mate is probably based in large part upon innate condi- 

 tions. The incident reported by Fulton (quoted in Chapter III) indicates that 

 "vigor" makes its natural appeal to the female. 



Behavior differentiates not only between the sexes but also between sexually 

 responsive and sexually indifferent individuals. Although the sexual impulse 

 probably may be stimulated to some extent by the advances of a potential mate, 

 yet in the main it tends to develop automatically. The rise of this impulse is 

 essential to the act of pairing. The choice of any male will thus be limited to those 

 females whose sexual periodicity is synchronous, or comes in the course of wooing 

 to be synchronous, with his own. 



Contiguity is also a factor. The continued confinement and isolation of two 

 birds will secure a mating when otherwise it would not occur. Confinement alone 

 is .sometimes efficacious, while at other times isolation from the sight and sound 



