The deadline was initially set for December then pushed back to February and extended this week to April 25, said Steve Segin, a spokesman for the U.S. Fish and Wildlife Service.
The service wants to give as many people as possible a chance to comment, he said.
The service has proposed listing the bird as threatened in Arizona, California, Colorado, Idaho, Nevada, New Mexico, Texas, Utah, Wyoming, Montana, Oregon and Washington, and in Canada and Mexico.
The bird's numbers have dropped from the thousands across the West to only 500 breeding pairs, with 10 pairs in Colorado, The Denver Post (https://tinyurl.com/lx4fmzc) reported Friday.
"It is a pretty unique bird. We're trying to do what we can within our existing constraints of dams, roads, bridges, railroads, highways," said John Toolen, an agency biologist based in Grand Junction. "We need to protect it."
Federal biologists say bringing back cuckoos will require taking advantage of natural floods, where appropriate, to restore their cottonwood habitat.
To create new pockets of cottonwoods around western Colorado, federal officials hope to team with river groups trying to control invasive tamarisk and Russian olives that thrive along tamed rivers.
Information from: The Denver Post, www.denverpost.com