Giraffes usually aren’t choosy about who they hang out with, but after they give birth females start to get selective, according to a new study. Researchers followed a group of the ungulates in Katavi National Park in Tanzania for several months between 2010 and 2011. They identified three female giraffes giving birth during this period and recorded clear changes in their herding pattern. Before giving birth, females formed flexible herds with random individuals, male or female, changing herd composition regularly. But after giving birth, the females formed tight groups composed of other mothers and their calves (pictured), the team reports this month in the African Journal of Ecology. On the rare occasions the scientists saw males joining this group, the guys left after a couple days. The authors think that these were likely cases of males looking for a mate. Calves are not able to walk long distances for their first 6 months, which makes them easy targets for predators. This type of mother-calves-only herd represents a more stable group of individuals that sticks together for several months, the researchers say. It also allows the moms to take better care of the young ones while some of the females take a foraging break. But why aren’t males part of these types of herds? The authors think that males are just not interested in protecting herds, but rather spend their time foraging and mating. Although such types of herds are known for other species, only sperm whales are known to change their herding behavior after giving birth.