GENETICS: COLE AND KIRKPATRICK 
355 
breeder has also found it difficult to explain the apparent excess of 
males which he commonly finds in the birds saved for breeding stock. 
The results here presented throw conclusive Hght on these and on other 
similar questions. 
Sex ratio. — ^The normal ratio of the sexes of pigeons hatched is 105 
males to 100 females. 
Death rate, — The death rate of squabs is especially high for the first 
two or three days after hatching, and at about 10 to 15 days of age. 
Differential mortality. — (1) When the two squabs from the same 
clutch of eggs are of distinctly different size before the banding age 
(10 to 15 days) the larger squab is more often a male than a female. 
(2) The death rate for the two sexes in bisexual broods is essentially 
equal. (3) There is no marked tendency for one sex to be weaker than 
the other in bisexual broods, and there is only a slight indication that 
more males than females from such broods survive to adult life — placed 
at 6 months. (4) A consideration of the ratio of males to females in 
each of the age groups defined^ does not indicate a high relative mortality 
of females in the ages preceding the adult stage. (5) There is a high 
mortality of both sexes during the first two or three years of their adult 
life, and this is especially high in the females between the ages of one 
and two years.' (6) The higher mortality of females at early adult 
ages, together with the higher proportion of males hatched (105: 100), 
may be in large part responsible for the prevaihng notion of a consider- 
able excess of male pigeons in adult populations and seems to furnish 
real substantiation for this notion. The fact that males are generally 
more easily recognized than females probably adds to this impression. 
Ratio of bisexual to unisexual broods. — (1) The number of unisexual 
broods, in which the squabs are either both male or both female, some- 
what exceeds in our records the bisexual broods (one squab of each sex), 
but the odds against the numbers obtained representing a potential 
equality are very slight. These facts are directly contradictory to the 
commonly accepted statement that the two eggs usually produce a 
male and a female squab. (2) Considering only the unisexual broods, 
the number of 'both males' to 'both females' is practically equal. 
Sex with respect to order of laying. — A comparison of the numbers of 
each sex hatched from first eggs and from second eggs respectively, 
shows no tendency for the former to produce exclusively males and the 
latter females but, as a matter of fact, more males than females are hatched 
from both. 
Time of laying. — (1) The mean time of laying of the first egg is about 
5 p.m., and of the second egg about one o'clock of the afternoon of the 
