Wind turbines are killing off an endangered species of bat at a much faster pace than expected, according to a study from the University of California.

The study found that the hoary bat population could decrease by 90 percent over the next 50 years as people build more wind turbines, according to the Daily Caller.

The results of the study suggest that construction of wind turbines would threaten the existence of migratory bats in North America.

“This new study is a clear warning signal that action is needed before the hoary bat population plummets and needs heroic measures to prevent its extinction,” Jamie Rappaport Clark, president of the environmental group Defenders of Wildlife, said in a statement.

Hawaii’s five major wind turbine farms are killing the hoary bats, Hawaii’s only native land mammal, about three times faster than predicted.

According to the U.S. Fish and Wildlife Service, which supported the study, the estimated population of the bats on all the islands range from a few hundred to a few thousand.

The wind farms have killed 146 out of the 187 Hawaiian hoary bats they are allowed to kill by 2030. The turbines have also killed 50 of Hawaii’s state bird, an endangered goose called the nene.

A peer-reviewed study from Wildlife Society Bulletin from 2013 said that 888,000 bats and 573,000 birds are killed each year by wind turbines.

By 2030, wind farms are projected to kill 1.4 million birds each year.

According to a 2015 report from the Daily Caller, America’s wind turbines in the last five years killed more than three times as many birds killed in the BP oil spill.