the spring.
The mare is in season in spring and summer; sheep take the ram in
autumn.[128] Many of the menstruating monkeys also, whether or not sexual
desire is present throughout the year, only conceive in spring and in
autumn. Almost any time of the year may be an animal's pairing season,
this season being apparently in part determined by the economic conditions
which will prevail at birth. While it is essential that animals should be
born during the season of greatest abundance, it is equally essential that
pairing, which involves great expenditure of energy, should also take
place at a season of maximum physical vigor.

As an example of the sexual history of an animal through the
year, I may quote the following description, by Dr. A.W.
Johnstone, of the habits of the American deer: "Our common
American deer, in winter-time, is half-starved for lack of
vegetation in the woods; the low temperature, snow, and ice, make
his conditions of life harder for lack of the proper amount of
food, whereby he becomes an easier prey to carnivorous animals.
He has difficulty even in preserving life. In spring he sheds his
winter coat, and is provided with a suit of lighter hair, and
while this is going on the male grows antlers for defence. The
female about this time is far along in pregnancy, and when the
antlers are fully grown she drops the fawn. When the fawns are
dropped vegetation is plentiful and lactation sets in. During
this time the male is kept fully employed in getting food and
guarding his more or less helpless family. As the season advances
the vegetation increases and the fawn begins to eat grass. When
the summer heat commences the little streams begin to dry up, and
the animal once more has difficulty in supporting life because of
the enervating heat, the effect of drought on the vegetation, and
the distance which has to be traveled to get water; therefore,
fully ten months in each year the deer has all he can do to live
without extra exertion incident to rutting. Soon after the autumn
rains commence vegetation becomes more luxurious, the antlers of
the male and new suits of hair for both are fully grown, heat of
the summer is gone, food and drink are plentiful everywhere, the
fawns are weaned, and both sexes are in the very finest
condition. Then, and then only, in the whole year, comes the rut,
which,