466 
Bulletin Xo. 162.—1915. 
included some, though comparatively few, records of other breeds, 
especially Homers, which have been used only to a limited extent 
in our studies. Considering the diversity of origin of the Tumbler 
stock and the other inclusions it seems quite probable that the ratio 
of 105 males to 100 females may be taken as the sex ratio for domestic 
pigeons generally. 
Although the sexes have been determined at different ages in 
different birds, the combined figures give the sex ratio of all birds 
hatched whose sex has been determined. There are included, it is 
true, 81 birds that had not succeeded in emerging completely from the 
shell at time of death, but whose sex was nevertheless determined. 
They were therefore recorded technically as “dead in shell,” rather 
than “hatched;” but for reasons which will appear it has seemed 
inadvisable to separate these birds from those which died within the 
first few days after hatching. Of these birds “dead in shell,” 44 
were males and 37 females; their exclusion would give a slightly 
lower ratio of males actually hatched, but the change would probably 
not be significant. 
Is there a Differential Mortality ? 
Darwin suggested two explanations for the apparent preponderance 
of males among adult pigeons; first, that males are produced in 
greater numbers; second that they live longer, or in other words, that 
there is a higher relative mortality among the females in early life.* 
The data here presented seem to show fairly conclusively that his 
first supposition is correct, that there is a slightly greater production 
of males; but it is doubtful if this excess is great enough to be noticed 
ordinarily and to account for the prevailing impression. As to a 
possible differential mortality, Darwin (1875, p. 247) states, on the 
authority of Mr. Harrison Weir, that when the nestlings are of 
opposite sexes, “the hen is generally the weaker of the two, and more 
♦Aristotle (1910, 613 a 24 — 29) says of ring-doves and turtle-doves, ‘‘The male, as a general rule, 
is more long-lived than the female; but in the ease of pigeons some assert that the male dies before 
the female, taking their inference from the statements of persons who keep decoy-birds in captivity.” 
