506 
Bulletin No. 162.—1915. 
May 4, 1914. A pair of Mourning Doves observed “looking over the location;” 
their behavior indicated that they would probably nest soon. 
May 7. Foundation of nest laid at place where birds were previously seen. 
May 10. Nest apparently complete; no eggs; birds not in evidence. 
May 12. First egg laid before 8 A. M. (no record of time of last observation on 
day previous). 
May 13. Second egg laid between 8 and 9 A. M. 
May 14. Birds incubating. 
May 23. Two eggs with dead embryos of Ring dove (Turtur risorius ) substituted 
for the Mourning Dove eggs; the latter placed in an incubator. 
May 26. Mourning Dove eggs both hatched in incubator during night; period of 
incubation 13 days from laying of second egg. 
May 28. Mourning Doves still incubating. 
May 29, 1:30 P. M. Mourning Dove on nest. 
May 30, 8:30 A. M. Mourning Dove on nest. 
10:30 A. M. Nest deserted; birds not seen around it thereafter. Still 
contained the substituted eggs, thus showing it was not 
an accident to the eggs which caused the termination of 
incubation. 
While this is but a single case, the evidence it furnishes is positive, 
and there is no reason to believe it is not about what might normally 
be expected under similar circumstances. The points of interest to 
us may be summed up briefly: 
1. The period of incubation for both the Mourning Dove eggs was 
13 days from the time of laying of the second egg. 
2. The parent birds continued to sit on the substitute eggs for 
four days after their own eggs had hatched, which is 31 percent, of 
the period of incubation of their own eggs. In the domestic pigeons 
the “factor of safety” was determined as 6 days, or 35 per cent, of 
the mean period of incubation. 
It is interesting to note that desertion of the eggs by the Mourning 
Doves occurred after 8:30 in the morning and before 10:30. If 
their habits with respect to the division of labor in incubation are 
similar to those of pigeons, the male sitting approximately from 
10 A. M. to 2 or 3 P. M., this probably means that it was the male 
bird which first failed to continue the extended incubation of the 
refractory eggs. 
