Deer reproductive cycles are the periods in which a doe can conceive. There are four periods, and conception is least likely during the first one.
A doe is in heat for approximately 30 hours. If she does not conceive or if there is no copulation, the heat cycle begins again in 28 to 30 days. During the mating season, or rut, males become increasingly more aggressive. They spar with each other in competition for females, using their antlers to test each other’s strength and gain mating rights.
The female usually enters estrus during late October and early November, triggered by shorter periods of daylight. Reproduction takes place with mature females that are about 1 to 2 years old. When pregnancy occurs, the gestation period is 10 months. When the female is ready to give birth, she leaves the herd and births in areas of dense vegetation, away from predators. Females give birth to one to three spotted fawns in mid to late spring.
In areas with abundant food, water and shelter and reduced predation by humans or other predators, deer reproduce quickly.