Though chimps are strictly daytime animals and avoid any activity during the night because their historic main predators, leopards, hunt at night, chimps in a national park in Uganda have been filmed raiding farmers’ fields inside the park’s borders.
Camera traps have caught wild chimpanzees in the act as they carried out night-time raids on farmland. The footage, captured by researchers from the Museum of Natural History in Paris and the Uganda Wildlife Authority, shows the chimps adapting to human pressure on their habitat.
The team says this is the first record of “frequent and risky” nocturnal raids to find food.
It is published in the journal Plos One.
The researchers carried out their study in Kibale National Park in Uganda, setting up their camera traps on the edge of the park.
“[It’s] surrounded on the outside by smallholder farms, forest fragments and tea estates,” the researchers said in their paper.
They think that humans encroaching on chimp habitats may have “promoted” the animals’ foraging trips into cropland. But the scientists were still surprised by how daring the chimps’ raids were.
Groups of about eight chimpanzees took part in each raid; these groups included vulnerable animals, such as females with clinging infants.
They would raid during the day as well, but during night-time raids the chimps stayed longer in the maize fields. They also showed fewer signs of vigilance and anxiety, such as looking around or scratching themselves roughly – a recognized signal of stress.
Dr Catherine Hobaiter, an expert in chimp behavior from the University of St Andrews, said the observations were fascinating. Habitat loss, she explained, was a much greater threat for the chimpanzees than natural predators.
“It forces chimps to explore new food sources, like human crops,” she told BBC News.
“Raiding fields is extremely dangerous – chimps may be attacked or even killed by people defending their crops, but by raiding at night [these chimps] seem to have reduced this threat.”
Despite how adaptable the chimps have shown themselves to be, Dr Hobaiter says the behavior is also worrying.
“Such a dramatic change suggests the chimpanzees are responding to a very strong pressure to obtain the basic foods they need to survive – a response to the widespread destruction of their natural forest home.
“While it might be working for now, this won’t be a long-term solution.
“As local people become aware of these nocturnal raids they may try to defend their fields in the dark, and the risks of conflicts escalating and injury to both chimps and people is likely to increase,” she said.
“From a conservation perspective, the only long-term solution is the protection of the remaining forests.”