It was a discovery that changed what researchers knew about the hunting techniques of chimpanzees. In 2007, Jill Pruetz first reported savanna chimps at her research site in Fongoli, Senegal, were using tools to hunt prey. That alone was significant, but what also stood out to Pruetz was the fact that female chimps were the ones predominantly hunting with tools. It was a point some dismissed or criticized because of the small sample size, but the finding motivated the Iowa State University anthropology professor to learn more. In the years following, Pruetz and her research team have documented more than 300 tool-assisted hunts. Their results, published in the journal Royal Society Open Science, support the initial findings -- female chimps hunt with tools more than males.

Generally, adult male chimps are the main hunters and capture prey by hand. Researchers observed both male and female chimps using tools, but more than half of the hunts -- 175 compared to 130 -- were by females. While males made up about 60 percent of the hunting group, only around 40 percent of the hunts were by males.

"It's just another example of diversity in chimp behavior that we keep finding the longer we study wild chimps," Pruetz said. "It is more the exception than the rule that you'll find some sort of different behavior, even though we've studied chimps extensively."

Both male and female chimps primarily pursued galagos, or bush babies, in tool-assisted hunts. Pruetz says the chimps used a spear-like tool to jab at the animal hiding in tree cavities. She added that one explanation for the sex difference in tool use is that male chimps tended to be more opportunistic.

"What would often happen is the male would be in the vicinity of another chimp hunting with a tool, often a female, and the bush baby was able to escape the female and the male grabbed the bush baby as it fled," Pruetz said.