It’s still a few years too early to mourn the passing of “Survivor,” the reality show that launched the genre more than six years ago. But as the CBS series wraps its 13th iteration this Sunday with sagging ratings it’s likely CBS is contemplating changes to revive the series.

At least for now, CBS isn’t saying what those changes might be, only that a 14th “Survivor” will debut early next year.

But media researchers say two changes CBS ought to consider are moving it off Thursday nights and airing just one cycle per year, cutting back from two. Fox’s “American Idol” airs once a year, and NBC will soon cut “The Apprentice” back from two to one cycle.

Researchers believe there’s nothing wrong with “Survivor” as a show, just where and how often it is scheduled. Giving it a rest would give viewers time to long for its return.

“It’s getting old and it’s starting to show its age,” says Michele Toller, senior national media manager at Empower MediaMarketing. “Perhaps airing fewer installments a year or moving it to another night, although that is very risky, may give ‘Survivor’ the shot in the arm it needs.”

“Survivor” by most measures is still doing well. Its average audience so far this season is 15.7 million viewers, ranking No. 12 among all programs.

It’s just not doing well compared to past performances. For most of its seven seasons, “Survivor’s” two yearly cycles have averaged about 20 million viewers. That began to change last year when “Survivor: Guatemala” and “Survivor: Panama” had an average audience of just under 17.5 million people.

Much of “Survivor’s” decline reflects stiffer competition CBS has come to face Thursday nights in the last several years. CBS’s rating in the 18-49 demographic on Thursdays is down 25 percent this year from last year, and it’s now slightly trailing ABC, which is up 159 percent.

CBS has been hurt by ABC’s moving “Grey’s Anatomy” to Thursday facing “CSI,” which has knocked that show from its post as the night's most-watched, and the launch of ABC’s “Ugly Betty” at 8 p.m., directly against “Survivor.” The rookie series is pulling in more than 13.5 million viewers, only about 2 million less than “Survivor.”

Media buyers say a disproportionate percentage of CBS’s ad revenue in primetime has recently been earmarked for Thursdays, which until this season consisted of “Survivor,” “CSI” and “Without a Trace,” which now airs on Sundays. Much of CBS’s Thursday revenue is now at risk.

“Car advertisers, movie advertisers and other entertainment advertisers use Thursday as a way to get people planning their weekends,” notes Brad Adgate, senior vice president and corporate research director at Horizon Media. “I don’t think [‘Survivor’] is in any danger of being canceled but perhaps CBS will move it to another night and move in a show that will do better in the time period.”

The trick, of course, will be finding that show.

Meanwhile, the 13th “Survivor” is heading into its finale with a whimper. This Sunday’s episode is expected to pull in fewer viewers than the 12th cycle’s finale did in May. That episode was watched by 17.1 million people, the first “Survivor” finale with fewer than 20 million viewers.

“Like any other show, it’s subject to audience erosion,” says Adgate. “You can’t expect to sustain the viewing levels that it’s had. ‘American Idol’ is an anomaly with its ratings going up every year. But even that show at some point will decline.”