Figure 9.12 Offspring sex ratios in red deer. (a) Yearling deer produce a low proportion of male fawns, but this proportion increases in older deer. (b) Among yearling deer, the proportion of male fetuses is initially high but then declines as gestation continues throughout the winter as female deer selectively abort male fetuses. Error bars are standard errors.
Data from T. Landete-Castillejos et al., Age-related foetal sex ratio bias in Iberian red deer (Cervus elaphus hispanicus): Are male calves too expensive for growing mothers? Behavioral Ecology and Sociobiology 56 (2004): 1–8.