Compared with Africa's other big animals, hippos have been relatively neglected in scientific research. Partly, this is because they're hard to study and dangerous to encounter.
Hippos tend to live in wetland areas often partly submerged in rivers, lakes and swamps - habitats that overlap with areas where people live, farm and fish. Though hippos are plant-eaters and don't see humans as food, they're highly territorial and aggressive in water. Along with their huge teeth and sheer size, this makes them one of the deadliest large mammals in the world: around 500 people are killed by hippos each year.
Other factors make their populations hard for people to track and manage. For instance, hippos are particularly hard to sedate and move, as they tend to run into water as soon as they are darted and risk drowning. Even if they're still alive, no one wants to fish a drowsy one-tonne animal out of murky water that may be home to other hippos or crocodiles.
But these challenges must be overcome, as hippos are such ecologically important animals. Their feeding habits shape vegetation patterns along water courses, and their dung contributes to aquatic food webs, supporting many fish and invertebrate species. In many regions, they are also a significant attraction for eco-tourism.
However, common hippos (one of two species in the hippo family, along with pygmy hippos) face numerous threats, primarily from human activities.
Over the past century, hippos have lost much of their original habitat. They've been illegally poached for their meat and ivory, or killed as retribution when coming into conflict with humans. This has caused their numbers to reduce and their populations to fragment. A century ago, it is estimated that several hundred thousand hippos lived in Africa, but just 130,000 or so are alive today.
At present, common hippos are officially classified as vulnerable, indicating they are threatened with extinction in the wild. This highlights why we urgently need accurate data on where and in what numbers hippos can be found, in order to inform effective conservation efforts.
Why we need data to conserve hippos
Geographic range maps, distribution records and population estimates are essential tools for tracking and protecting hippos. There are some hippo maps already available, such as this one produced in 2017 for the world's official inventory of conservation status, the IUCN Red List:
However, these maps are often based on outdated data and sometimes entirely omit important regions. For instance, the above map shows hippos along the coast of northern Namibia, yet a local expert I spoke to says they haven't been seen there since the 1970s.
The creation of a standardised, comprehensive hippo database would be an important milestone in hippo conservation efforts, and would help mitigate conflicts between humans and hippos. Surveys of hippo populations also need to be standardised across the continent to ensure consistency in data collection and analysis. This would allow for better comparisons between regions, helping us to see how different threats are affecting hippos in different places.
One model that has worked well is the African Elephant Database, which has become an important resource for managing populations and informing conservation efforts across the continent. Since no such database currently exists for common hippos, there is a significant gap in our understanding of the species' needs and challenges.
An updated database
Colleagues and I have begun to address these data gaps, with a comprehensive review of common hippo distribution records and population estimates across southern Africa from 2003 to 2023.
Our work, published in the journal Biological Conservation, reveals population estimates are lacking in many areas. Additionally, we found that methods used to survey hippo populations across different countries and regions are inconsistent, which further complicates efforts to monitor populations accurately.
One of the key findings of our study is the critical importance of official transfrontier conservation areas. These areas provide crucial habitat as they often encompass systems of rivers, lakes and deltas that cross international borders and are large enough for hippos to move around and maintain genetically-healthy populations. The largest such area, the Kavango Zambezi, covers parts of five different countries.
For now, our map and database covers only the southern third of Africa. Eventually, we would like it to be extended across the continent, as most countries south of the Sahara have at least some small populations of hippos - or did in the recent past.
What we need to do now
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At a local level, it is important to balance agricultural practices and land use with the conservation of wetlands. Rather than draining wetlands, special barriers might be a better option to keep some distance between humans and hippos. Education programmes can help raise awareness of the cultural and ecological value of hippos - as well as their dangers.
Hippos can also be reintroduced into areas where they were historically present, as happened recently in Malawi. However, this approach is challenging, since hippos are so hard to immobilise and transport.
On a broader scale, we need a coordinated international effort to promote transfrontier conservation areas and develop an Africa-wide database and standardised survey methods. This would help secure the future of this iconic species.
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Hannah Lacy, PhD Candidate, Faculty of Biological Sciences, University of Leeds
