CHEYENNE, Wyo. (AP) — The government is preparing insufficient protections for a ground-dwelling bird that has declined significantly over the past century and soon will face a possible endangered species listing, according to 11 biologists who have studied the greater sage grouse.

Federal agencies have abandoned science-based conservation measures in favor of “more elastic, subjective measures” inadequate to address threats to the species, the scientists wrote Thursday to Interior Secretary Sally Jewell and Agriculture Secretary Tom Vilsack.

“We strongly encourage you to direct federal planners to finalize conservation plans that prescribe objective, measureable and robust conservation measures based on the best available science,” the letter said.

Federal agencies including the U.S. Bureau of Land Management have adopted sufficient protection for the bird, an Interior Department spokeswoman said.

“Interior believes strong protections in the BLM management plan are an important part of successful conservation of the greater sage grouse, and the Fish and Wildlife Service is working in close collaboration with them to ensure the best outcome for both the bird and the Western landscape it embodies,” said the spokeswoman, Jessica Kershaw.

The Agriculture Department did not respond to a request for comment.

Greater sage grouse inhabit 11 states. Their numbers have declined from perhaps well over 1 million in pre-settlement times to no more than 500,000 today.

The U.S. Fish and Wildlife Service plans to decide by Sept. 30 whether the bird warrants protection as a threatened or endangered species, though Congress has withheld spending to implement any such protection.

In the meantime, the Bureau of Land Management continues to amend local-level planning documents to include protections for the greater sage grouse. Those changes fail to incorporate science-based recommendations for regulating oil and gas drilling, mining, livestock grazing, prescribed burns and other activity near sage grouse breeding areas, the scientists wrote.

Those signing included William Baker and Jeffrey Beck at the University of Wyoming and Edward Garton and Kerry Reese at the University of Idaho.

“We support the federal planning process and are prepared to assist your departments in developing measures to conserve and recover greater sage grouse, but federal planners must commit to science-based planning to achieve this goal,” the scientists wrote.

Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.