There may be nearly twice as many gorillas in the world than previously thought, a new study reveals.

Published in the journal Science Advances, the decade-long survey determined that there may be 361,900 gorillas in western equatorial Africa, higher than the earlier estimates of 150,000 to 250,000, the Guardian reports.

However, gorillas remain critically endangered as their populations continue to decline. According to the Guardian, the population has dropped 20% over the past eight years. Some 80% of gorilla troops are also believed to live in unprotected habitats, leaving them vulnerable to what the study describes as “guns, germs and [felled] trees.”

“The population could be double,” said Professor Fiona Maisels of the Wildlife Conservation Society, one of 50 international experts involved in the survey, the Guardian reports. “But that is not the big story. Just because there are rather a lot of them does not mean they are not very, very vulnerable.”

Poaching, deforestation and outbreaks such as Ebola jeopardize the survival of gorillas, especially because they breed so slowly. It takes females 11-12 years to mature, and they only give birth every four years.

“It takes a very long time to build populations back up,” Maisels said.

The survey was conducted in an area of western equatorial Africa roughly the size of France, bordered by the Atlantic Ocean, the Congo and Ubangi rivers.

The population of a central chimpanzee sub-species was also found to be 10-80% higher than previously thought.

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