You'll have to ask the hippo! Migrating animal encounters a three-tonne threat in Kenya's Mara river
Africa's great wildebeest migration is one of the wonders of the natural world. Every year, over two million animals make the trek between the Serengeti National Park in Tanzania and the Maasai Mara National Reserve in Kenya.
Moving en masse, they usually cross the mighty Mara river with little thought to the crocodiles lurking below the surface.
But this herd got a surprise when a three-tonne hippopotamus took exception to it plunging through his placid stretch of water.
These photographs capture the moment the mammal got to grips with a wildebeest for daring to enter his territory.
The hulking hippo swam across the Mara to confront the migratory horde, snapping at a solitary straggler.
It opened its jaws to a 150-degree angle before clamping them shut on the animal's hind legs and dragging it under the water.
The dramatic moment was caught on camera by amateur photographer Sjoerd van Berge Henegouwen who was visiting the Maasai Mara in Kenya.
Sjoerd, a 45-year-old criminal laywer from Maastricht, Netherlands, said: 'By this time of the year most of the 2.3 million wildebeest have migrated from the Serengeti to the Maasai Mara.
'I was very lucky that this big herd hadn't done so. I was watching the crossing and expecting a crocodile to go for one of the wildebeest when I suddenly saw the hippo.
'He was very aggressive and you could tell it was defending its territory.
'He deliberately blocked the wildebeest and when they went to go around he went for one of them.
'He bit into its back and the force of that caused the wildebeest to go under the water. I never saw it come back up.
'I was slightly amazed by what I saw as both hippos and wildebeest are grazing animals and you would think they could get along.'
Although hippos are herbivores, they are notoriously aggressive and will go on the attack to defend their territory or young.
Frequent targets of their aggression even include crocodiles, which share hippos' river habitat and are known to prey on their young.
Hippos are very aggressive towards humans, whom they commonly attack whether in boats or on land with no apparent provocation.They are widely considered to be one of the most dangerous large animals in Africa.
The wildebeest migration also includes hundreds of thousands of gazelle and zebra. It is less predictable than other migrations, with the animals constantly rotating between the Serengeti and Maasai Mara in an endless search for food and water.