hippo partially submerged in the water basking in the morning sun while a yellow billed oxpecker perched on its back picks

hippo head resting submerged water sleeping basking sun morning river wild wildlife serengeti national park tanzania hippopotamus african conservation vulnerable amphibious nature dangerous safari retima pool wallowing eyes open side view profile closeup portrait wet skin gleaning yellow billed oxpecker back parasites perched picking mutualism symbiotic relationship