216 WALLACE CRAIG 



courting performance and the egg-laying. This was observed in 

 the year 191 1 in two cases, and in 1912 in twenty-four cases, 

 involving six birds. A very significant detail is, that as the 

 three pairs of females in 191 2 were kept in one room, with no 

 other birds in the room, the three pairs showed a marked ten- 

 dency to keep time with each other in their laying. Each pair 

 could not see the other pairs, but when they heard their excited 

 cooing and kahing and running about, the tardiest pair were 

 thereby stimulated and brought into similar activity. 



The mate is not the only environmental factor in determining 

 the time of egg -laying in the dove. As Professor Whitman said 

 to me: "A great many factors enter in. Even if the female has 

 the male, if she has no nest box and no nesting conveniences 

 she may not lay. The egg develops and passes down the oviduct 

 by degrees corresponding to the whole activity of the pair. It 

 takes a week to ten days (in the domestic pigeon). This is 

 true whether the pair are building their first nest or are pre- 

 paring for a second brood. If, when the female is ready the male 

 is not, she waits for him." In order to prevent birds from lay- 

 ing too late in autumn or too early in spring, Professor Whitman 

 found that it was not always necessary to separate the sexes: 

 he could keep mates together but with no nesting facilities, 

 nothing to "go to work with," and this prevented their breed- 

 ing. An excellent account of this matter is to be found in a 

 paper by Harper (1904). That the female pigeon will refrain 

 from laying if conditions do not satisfy her, has been so long 

 known to breeders that it is mentioned by Aristotle (1891), 

 who says, "Pigeons are able to retain their eggs even in the 

 act of parturition. If they are disturbed by anything occurring 

 in the neighbourhood of their nest, or a feather be plucked out, 

 or if anything else troubles or disturbs them, they retain the 

 egg they were about to lay." In two cases among my doves 

 this year I observed a bird hold back her egg at the time of 

 parturition, because she was kept away from her nest. How- 

 ever, when the egg is fully developed and ready to lay, the 

 bird's power to retain it is evidently limited. The real control 

 of the production of eggs is earlier, connected with the ovary 

 itself and the process of ovulation. 



Professor Whitman had one season a solitary female American 

 robin, which built a nest by herself and laid a set of eggs in it. 





