Despite limits on drilling put in place to protect the greater sage grouse, oil and gas development in the Western U.S. could continue to cause a decline in numbers, according to The Associated Press via Flathead Beacon.

After observing the effects of drilling on the sage grouse population over 25 years, U.S. Geological Survey and Colorado State University researchers reached their conclusion. The bird population dropped 14 percent annually in areas with at least 10 oil or gar wells per square mile. Populations remained stable where no wells were present.

Rather than putting the sage grouse on the endangered and threatened species list, despite the long-term decline, the U.S. Interior Department blamed oil and gas development, grazing, wildfires, residential development and disease. It acted by putting limits on drilling targeted at preserving the bird’s breeding grounds in Wyoming, Montana, Colorado and eight other states.

The new regulations allow companies to construct one well pad per square mile, with each pad containing multiple wells — a limit that could potentially eclipse the threshold found to be dangerous during the study.

Learn more: Flathead Beacon > Researcher: Limits on Drilling Not Enough to protect Sage Grouse