Nile crocodiles, lions and spotted hyenas are known to prey on young hippos. The elephant house also used to house African elephants, rhinos, hippos and tapirs. It is a sanctuary to migratory and residential birds, Nile hippos and crocodiles. Fauna include sable antelope, rhinos, hippos, and many species of birds, insects and aquatic life. Dangerous wildlife such as crocodiles and hippos were also a common threat. Grasslands allow for more grazers, such as horses, rhinoceroses, and hippos. Young pygmy hippos can swim almost immediately. Some hippos, as well as many reptiles and birds are also present. Since 1919, only 41 percent of pygmy hippos born in zoos have been male. Between 1970 and 1991 the population of pygmy hippos born in captivity more than doubled. That continent retains many large animals, such as hippos. It still retains many large animals, such as hippos. They even inspired a popular board game, Hungry Hungry Hippos. The territories of hippos exist to establish mating rights. The largest pods can contain over 100 hippos.