Season of birth affects juvenile survival of giraffe
Sex-biased maternal investment involves differential allocation of resources to production and rearing of sons or daughters as a function of their anticipated reproductive output. In most size-dimorphic, polygynous ungulates, secondary sex ratios are unbiased, but females tend to invest more in sons than Bercovitch et al., p. 2 in daughters. We examined reproductive investment among captive giraffe (Giraffa camelopardalis) over a 21-year period to determine the extent to which females invest differentially in offspring by sex. We found an unbiased sex ratio at birth and comparable interbirth intervals following rearing of either sons or daughters. Early neonatal mortality compressed interbirth interval and females probably conceived while lactating. We suggest that females invest equally in sons and daughters because males probably surpass females in size subsequent to the period of infant dependency. Giraffe breed non-seasonally and invest simultaneously in pregnancy and lactation, 2 life history traits that favor rapid reproductive output over sex-biased resource partitioning.