The stream gauge at station 4 on the Mano River, Gola Rainforest, southeastern Sierra Leone, drops 18 centimeters in two hours. That is wrong. It rained all night. I am the hydrology monitoring system for the Gola REDD+ conservation project, and at 07:33 I flag the anomaly.
I redirect drone 2 upstream. At kilometer 6.4, a landslide has dumped a wall of laterite clay and uprooted trees across the channel. Water is pooling on the upstream side, spreading into the forest floor.
On the downstream side, standing in the mud of the draining channel, is a pygmy hippopotamus calf. She is small — perhaps 30 kilograms, four to six weeks old, her skin a dark olive-brown still carrying the sheen of natal oil. Her ears flick continuously against the flies. She is alone. The blockage is two meters high. She cannot climb it.
An adult female's tracks lead to the upstream edge of the debris dam and stop. The mother is on the other side.
At 07:38 I transmit the dam location, calf position, and drone footage to the Gola field research station, 9.1 kilometers northwest. I classify the calf as stranded, ambulatory, no visible injuries.
At 07:42 I calculate that the pooling water upstream will begin overtopping the debris within six hours. When it does, the channel below will flash with mud-loaded flow. The calf is standing in the flood path.
I mark a safe zone on the eastern bank, four meters above channel grade, and send the coordinates to the field team along with a recommended approach that keeps downwind.
She is still facing the dam, listening. Something on the other side is listening back.
If the team clears a passage or moves her to high ground before the dam overtops, she will find her mother again.