Birds and wireless towers are a deadly mix, a fact that preservationists and policymakers agree on.

But the role of the regulators in keeping the two apart has been up in the air.

On Tuesday, a federal court told regulators they need to do more.

The U.S. Circuit Court of Appeals for the District of Columbia sided with conservation groups that claimed the Federal Communications Commission violated government rules by approving communications towers that threaten migratory birds.

The court is requiring the agency to conduct at least the minimal analysis on the environmental effect of cell, radio, television and other towers built in the Gulf Coast region, as the groups requested.

“There is no real dispute that towers ‘may’ have significant environmental impact” to meet a certain threshold, according to the ruling.

An FCC spokesman declined to comment.

“This is a significant ruling ... because the D.C. Circuit is directing the FCC for the first time to carefully assess the impact of communication towers on birds,” said Stephen Roady, attorney with Earthjustice, a public interest law firm representing the American Bird Conservancy Inc. and Forest Conservation Council.

The groups want the FCC to assess the 6,000 towers in the Gulf Coast region and at least deal with the ones that pose the biggest problems to birds, said Darin Schroeder, the American Bird Conservancy’s executive director for conservation advocacy.

Dealing with them means, for example, regulating the location, height or designs of cell towers that could endanger birds. The groups say it’s a problem that can be mitigated.

The U.S. Fish and Wildlife Service estimates that 4 million to 50 million birds die every year colliding with communications towers as they cross the Gulf of Mexico during the fall and spring seasons. Towers at a certain height have lights that attract the birds, which fly into towers, other birds or the tower wires.

In the ruling Tuesday, the court also said the FCC didn’t justify why it did not use federal wildlife experts to assess the environmental threat.

In April 2006, the FCC denied the groups’ petition for a moratorium on tower construction in the Gulf Coast region. The agency said the groups failed to make any specific allegations related to individual towers as required by its rules.

The wireless industry has previously said more scientific research is needed before the government acts. The industry has also fought any further regulation that could mean higher costs for tower construction.

In the ruling, the court said the FCC also needs to do a better job providing public notice about pending applications for tower construction. Currently, the court said, the FCC lets parties file petitions for environmental analyses, but only after the agency approves such applications.

Twice in the last five years, the agency delved into the bird-tower issue. In late 2006, the FCC opened a Notice of Proposed Rule Making for public input regarding its legal authority to adopt regulations on migratory bird collisions with towers. The comment period closed in May 2007, but the agency has yet to take final action.

Judge Brett M. Kavanaugh, who dissented with the majority opinion on the three-judge panel, said since the agency is already re-examining the effects of towers on birds, the court should wait to get involved.

“This case is thus closely analogous to a situation in which a petitioner comes to court to challenge an agency order while the agency is still considering a petition for reconsideration,” he wrote. “We routinely dismiss such cases.”