These endangered monkeys kept getting hit by cars. Scientists had a clever solution.

Endangered primates that are frequently killed by cars while trying to cross the road in a national park in Zanzibar have been given a lifeline after scientists put in speed bumps to slow down traffic.

Zanzibar red colobuses (Piliocolobus kirkii) are small primates with a white coat, red back and black face. They are currently listed as an endangered species, with fewer than 6,000 mature individuals left in the wild, according to the International Union for Conservation of Nature (IUCN) Red List of endangered species. The species is endemic to Unguja — the largest island in the Zanzibar archipelago in the Indian Ocean — and most individuals now live within Jozani-Chwaka Bay National Park.

However, despite being a protected species within a safeguarded area, these small primates are still under threat from humans, scientists report in a new study. Red colobuses are frequently hit by cars as they try to cross the main road through the park. In response, a group of scientists from Bangor University, the Wildlife Conservation Society (WCS) and national parks in Zanzibar installed four speed bumps along the road.
"After the road at Jozani was surfaced but before the speedbumps were installed, a colobus was reported to have been killed every two to three weeks, resulting in perhaps about 12% to 17% annual mortality," lead author Harry Olgun, a doctoral student at Bangor University in the U.K., said in a statement.
Since they installed the speed bumps, the rate of collisions between cars and red colobuses has halved, according to the researchers. "The recent data show that speed bumps have made a huge difference for the safety of the colobus," Olgun said in the statement.

However, collisions with cars still remain a big risk.

"Cars are not selective in the animals they kill," co-author Alexander Georgiev, a primatologist at Bangor University and director of the Zanzibar Red Colobus Project, said in the statement. In the wild, predators target the youngest and oldest individuals in the population, but cars are "equally likely to kill reproductively active young adults," which could stop the population from rebounding, Georgiev said.
However, the researchers still believe there is hope for these adorable primates.