Madagascar hippopotamus is a forest dweller

The extinct pygmy hippopotamus that once roamed Madagascar lived in forests rather than the open grasslands preferred by the common hippopotamus on the African continent, researchers at the University of Cincinnati have found.

The findings suggest that the grasslands that now cover most of the large island off the east coast of southern Africa is a relatively recent human-facilitated change rather than the natural habitat partially maintained by these famous large vegetarians.

This study is published in the journal Plants, People, Planet.

When Madagascar broke away from mainland Africa 150 million years ago, its plants and animals evolved in geographic isolation in the Indian Ocean. Madagascar did not have the elephants, giraffes, rhinos or other large mammals found on the mainland today.

But there are hippos.

The size of a cow, the pygmy or Malagasy hippopotamus is much smaller than its four-tonne cousin, the common hippopotamus. Even so, the Malagasy hippopotamus is one of the largest land animals on the island along with the Nile crocodile and the enormous flightless elephant bird.

The hippopotamus may be similar to the secretive and endangered pygmy hippopotamus found in the forests and swamps of Liberia and Guinea, West Africa, said Brooke Crowley, a UC professor of geosciences and anthropology and lead author of the study.

“Ecologically, we think the Malagasy pygmy hippopotamus is fairly close to the pygmy hippos that live in the forests of West Africa,” said Crowley.

Crowley and his research colleagues conducted an analysis of stable carbon and nitrogen isotopes found in the bones of an extinct Malagasy pygmy hippo that roamed the island more than 1,000 years ago. This isotope, found in animal bones, leaves fingerprints of the food they eat. And this provides clues about their preferred habitat.

Researchers took samples from the bones of the pygmy hippo at the museum along with those the team collected on the island. They found that the pygmy hippopotamus did not regularly graze on grass in dry, open habitats, even in areas currently dominated by grasslands. Instead, they prefer plants found in wetter woodland landscapes. This suggests that forests were more abundant before people started changing the landscape to grow crops, graze cattle and domestic goats and obtain firewood and building materials.

The common land hippopotamus loves grass. Their name comes from the Greek word for “river horse”. Every night they left the safety of rivers and waterholes to seek fresh pasture, cultivating grass like horses, before returning in the morning.

But the researchers’ analysis found that grass represented only a small fraction of the Malagasy pygmy hippo’s diet. Instead, they behave more like browsers, eating reeds and leaves. As a result, the hippopotamus likely had little influence in maintaining or expanding the island’s grasslands.

“Over the years we have seen evidence that these animals were not grazing,” said Laurie Godfrey, study co-author and emerita professor at the University of Massachusetts Amherst.

Godfrey said there is evidence to suggest that humans caused the extinction of the island’s hippos when they created permanent communities and moved from hunting and gathering to raising pets and growing crops. He calls his idea the “Subsistence Shift Hypothesis,” which he says is an elaboration of a similar idea first proposed by renowned archaeologist Robert Dewar.

“There is fairly convincing convergent evidence to suggest that many extinct animals disappeared in short periods of time coinciding with the human transition from hunting and gathering to grazing,” said UC’s Crowley.

Crowley thinks restoring native forest is key to helping preserve the island’s wildlife. Based on their study, the vast prairie was not a critical habitat, at least for the island’s hippos.

“Some colleagues argue that the prairies are ancient and we need to protect and manage them as we do the forests,” Crowley said. “I think that forests are much more important. We are not suggesting that grasses did not exist in the past, but are showing that there is no evidence of large treeless grasslands prior to about 1,000 years ago.”

That’s a point the researchers in this study made as well.

“It is clear that Madagascar faces a much bigger biodiversity crisis than it already has. Preventing this crisis will demand new conservation actions,” the study concludes.

This study was supported by grants from the National Science Foundation, the Fulbright African Regional Research Program and the National Geographic Society.