96 BEHAVIOR OF PIGEONS. 



27 days, 16 of which are devoted to the eggs and 11 to the young. The old birds 

 defecate out of the nest and remove the vacated shells and any dead young from 

 the nest. The young also manifest instinctive behavior conducive to the clean- 

 liness of the nest. 



(5) Both birds feed the young by regurgitation. These activities begin with 

 hatching and the duration of the period is highly variable. Feeding invariably 

 continues after incubation has ceased. Normally the feeding is terminated by 

 the events of the succeeding cycle. The female usually stops feeding with the 

 beginning of the second incubation period, while the male may continue well up 

 to the point of hatching. The food consists at first of "milk," a secretion of the 

 crop. Later this secretion becomes mixed with partially digested food. The 

 young birds stimulate the feeding response by certain attitudes of the body, their 

 cries, flapping of the wings, and the teasing stimulus of their beaks around those 

 of their parents. The old birds open and present their beaks, while those of the 

 young are inserted with vigorous thrusts. The machinery of regurgitation consists 

 of a shaking of the crop, involving movements of the entire body and especially 



of the wings. 



SPECIES DIFFERENCES. 



For purposes of reference the various comparative statements of the manu- 

 scripts may be summarized. There are probably specific differences in the time and 

 duration of the breeding-season. The essential similarity of Leucosarcia, Geopelia, 

 bronze-wing, mourning-dove, and the crested pigeon in their display and pre- 

 liminary courting activities is frequently commented upon. Band-tails deviate 

 from the usual procedure of mouth-billing as a preliminary to mounting. Mounting 

 behavior, up to the point of contact, is uniform, only differences in speed and vigor 

 being noted. The acts subsequent to union are highly variable with the species. 

 The recovery of position by the male is peculiar to the bronze-wing. In some 

 species the male drives the female away, while the opposite attitude is exhibited 

 by others. Uniformity is asserted as to the symptoms of nesting, the tendency 

 to seek a new nesting-site for subsequent cycles, the number of straws carried at 

 a time, and the male's manner of delivery. Apparently each species exhibits 

 distinctive voice characteristics, as is evident in their nesting-calls. Uniformities 

 are mentioned as to the method of egg-laying, the feeding activities, the roosting 

 habits of the male during incubation, feminine incubation at night, and the time 

 of interchange. Differences are noted in the length of the incubation period, the 

 number of eggs laid, the time of laying, and the time of beginning incubation. 



One can hardly regard this account as an exhaustive comparative study. 

 The manuscripts indicate that Professor Whitman was apparently more interested 

 in the general uniformities of behavior than in the matter of specific differences. 

 Close confinement under highly artificial conditions would tend to obscure or distort 

 many specific modes of response, such, for example, as the nesting activities of 

 wild species. A note in one of the later manuscripts indicates, however, that the 

 author at that time contemplated a very extensive study of species relationships 

 by means of comparative behavior. 



