Giraffes breed throughout the year, although birthing peaks have been observed in numerous populations, including Nairobi N. P. in Kenya Aug and Sep; Waza N. P.in Cameroon, November-January; Serengeti National Park, September; and Northern Namibia in December; and at different times of the year at Kruger N. P.; Calving peaks are often related to rainfall and seem to coincide with the production of new Acacia shoots that have a high protein content.
Van der Jeugd suggests that differences in ecological circumstances create different ways of mating. Giraffes in zoos also breed seasonally. A single calf is born, although twins have been recorded. The average gestation period is around 15 months while a captive individual gave consecutive babies only 420 days apart.
Juveniles are heavier in the wild around 101 kg than in captivity approx. 55 kg The mean height at birth is 1.8 m and 1.9 m for females and males, respectively. Calves nearly double in size in the first year, likely serving as an anti-predator strategy because calves are extremely vulnerable to predation.
Giraffe milk is high in fat about 13-17%, protein 6%, and ash, although the lactose concentration is lower than that of cow’s milk. The moment of weaning is variable: exceptionally up to two years, but generally around 9-12 months, although calves are able to eat solid food after the third or fourth week and begin ruminating at between three and four months
Calving intervals are 19 to 20 months. The ranges are similar in captivity, with a range of 14–38 months. The interval between parturition and conception is usually 4–9 months. The first conception was noted at 50 months in the Serengeti N.P. and 56 months in southern Africa In captivity, the mean age at first calving was 57 months.
Males reach maturity at 3 years old, but in the wild, they are probably excluded from reproduction by older bulls. Adult sex ratios have been recorded as being female-biased in Serengeti N. P., Nairobi N. P., Katavi N. P., Luangwa N. P., and Niger, while the opposite was true in Tsavo East N. P. In N. Namibia, sex ratios were different between subpopulations, although was unbiased across the overall population .The sex ratio at birth is 1:1.
Between 54% and 62% of a given population is over four years old. Mortality rates are strongly shaped by Lion – Panthera leo predation, especially on neonates. In Serengeti N. P., 58% of young Giraffes died during their first year of life while only 2% died at the age of four.
In Kruger N. P., first-year mortality was also high at 48%. The maximum years of the life of male giraffes, based on individuals from LuangwaValley, is shorter (22 years) compared with females (28 years); maximum longevity in captivity is recorded at 39 years.
Given the uniform sex ratio at birth, comparable mortality rates, suckling rates, and inter-birth intervals among juveniles, and the similar growth rate of calves while nursing, suggest that adult females invest equally in their offspring, regardless of sex, and that males surpass females in size only after the period of dependency.