As human development in Africa expands, the natural habitat of chimpanzees is shrinking across much of the continent. As a result, food sources are less abundant and contact between humans and chimps is more frequent.

Sometimes, that contact is obvious (and insidious) -- chimps caught in human snares. Sometimes, however, that contact happens in the dark of night unbeknownst to the people involved. For the first time, biologists have documented what they refer to as "frequent and risky" nighttime raids of neighboring farms.

In a new paper, published this week in the journal PLoS ONE, researchers from the Museum of Natural History in Paris and the Uganda Wildlife Authority detailed their observations of a group of thieving chimpanzees. In addition to the paper, there is video proof showcasing the stealthy chimp raids of a corn farm on the edge of Uganda's Kibale National Park.

"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," Dr. Catherine Hobaiter, a chimp expert from the University of St. Andrews, told BBC News. "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 the study suggests these particular chimps are having impressive success, Hobaiter says the adaptive behavior is as worrying as it is impressive. "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 added.

As risky as the behavior is, the video evidence suggests these chimps are less careful and more nonchalant than scientists might have expected. It seems the darkness of a new moon offers the chimps a chance to relax even while performing a raid. Some pairs even took a break from their thievery to copulate.