A study, released Friday, has revealed that the number of breeding males in the greater sage-grouse population of the United States and part of Canada has registered 56% decline in recent years. It has come as a sign of trouble for the ground-dwelling bird.

The study by the team from Pew Charitable Trusts was carried out because the US Fish and Wildlife Service will make a decision before the end of September on whether the bird should be protected under the Endangered Species Act or not.

US Secretary of Interior Sally Jewell has announced that a sub-species of the sage-grouse found in California and Nevada did not require protection under the Endangered Species Act. The decision was highly criticized by the environmentalists.

The announcement came as a victory for mining, energy and farming companies which fear sage-grouse protections, as they could restrict their livelihoods in the 11 Western states where the bird lives, including Washington, Colorado and Montana.

It is believed that millions of sage-grouse have once inhabited a broad expanse of the Western United States and Canada. In 2010, the US Fish and Wildlife Service estimated that between 200,000 and 500,000 birds are remaining.

The Pew Charitable Trusts study hasn’t given a complete estimation of the total number of sage-grouse birds that might live in their range in the 11 US states and a southern portion of the Canadian province of Alberta.

But according to the study in 2013, just 48,641 breeding males were found, representing a 56% decline from 2007 when the count was 109,990.

The lead researcher on the study, Edward Garton, said that sage-grouse populations show a great fluctuation, decreasing and then rebounding as a natural phenomenon.

He added, “Is it part of the typical cycle, or are the populations actually collapsing? We don't really know the answer to that”.