For over a decade the behaviours of mothers and newborn calves of Black rhinoceros Diceros bicornis michaeli and Reticulated giraffe Giraffa camelopardalis reticulata have been observed at Brookfield Zoo during the critical first few weeks post-partum. Consistent patterns were seen for individuals within species, allowing models of time budgets, including ranges of variability surrounding each behaviour, to be developed. Once the model is created any data collected for neonates can be compared to the mean values in the model so