The common hippopotamus, or hippo, is one of the world's largest living land mammals. Yet despite their size, these hefty giants spend around 15% of time 'suspended' in the air when running, say scientists.
This intriguing observation was made by researchers from the Royal Veterinary College in England whilst studying the footfall patterns and stride parameters of hippos.
The findings offer new information on hippo movement, which could be useful for understanding the evolution of locomotion, body size, habitat usage and ecology in hippos. The data could also be relevant to clinical veterinary care of hippos, especially the detection of lameness, say the researchers.
Hippos can reach speeds of up to 19 mph (30 kmh), often doing so to avoid lions, rhinoceroses, humans or each other.
But "basic information on the way hippos move is limited and sometimes contradictory," says John Hutchinson, a professor of evolutionary biomechanics who led the research.
Set on improving the base level of data around hippo locomotion, Hutchinson and colleagues aimed to test how their footfall and stride patterns change with speed. They also wanted to find out if hippos trot at all speeds and if they ever use an aerial or suspended phase (when all four feet are off the ground at once) during their movement.
The scientists analysed online videos alongside new video data collected from two zoo hippos. They gathered a sample of 169 strides from 32 individuals.
The study showed that at the fastest speeds hippos used brief aerial phases, spending up to 15% of their running time completely off the ground – a new discovery, according to the paper.
Hippos were found to be more athletic than elephants, but a little less athletic than rhinos.
The findings "prompt important questions about how locomotion evolved in Hippopotamidae," says Hutchinson, who also believes that the data will "help form a baseline for assessing if other hippos use normal locomotion; relevant to clinical veterinary assessments of lameness; and for reconstructing the evolutionary biomechanics of hippo lineages."
More amazing wildlife stories:
