• by Wayne Friedman , March 26, 2013

The drama around network late-night programming continues -- and NBC's "Tonight Show with Jay Leno" remains on top in many viewing categories through the first 11 weeks of 2013. But the show is slipping in one key area.

Through the first 11 weeks of 2013, "Leno" is at Nielsen live-plus-same-day 3.45 million total viewers -- down 8% versus a year ago. CBS' "Late Show with David Letterman" is at 3.03 million, off 5%; and new ABC's "Jimmy Kimmel Live" is at 2.569 million. "Leno" is also still ahead among 18-49 and 25-54 viewers.

But "Kimmel," which started after the new year, is now averaging more key 18-34 viewers than any other network show -- 315,000 viewers from Jan. 7 through March 17. In fact, "Kimmel" has topped all shows in recent weeks in March.

"Tonight" is averaging 309,000 viewers, down 9% against the same first 11 weeks of 2012; "Late Show" is at 270,000 18-34 viewers, off 10% from the same period a year ago.

For years, young-skewing marketers -- movie companies, soft drink companies and video game makers in particular -- have used late-night TV to grab young viewers' impressions, particularly with young men.

Reports suggest that "Kimmel" has put TV executives -- particularly those at NBC -- in a panic, because of these immediate shifts in ratings among younger viewers. In response, there are numerous reports that Jimmy Fallon of NBC's "Late Night" would soon take over for Leno -- possibly in February 2014, right after NBC's Sochi Winter Olympics has concluded.

Previously, NBC spent some five years prepping Conan O'Brien to take over Leno's job -- only to let him go after a few months on the job in January 2010 -- after starting up in June 2009. NBC will move much faster this time around, say TV executives.

"You don't have a lot of time," says Kevin Aratari, executive vice president of entertainment marketing of Los Angeles-creative entertainment ad agency mOcean. "Trends change in the industry all the time." In regard to Fallon, Aratari believe his much younger profile against that of Leno will have some immediate impact. "He already has a good presence online; he is a big Twitter user."

It's not just young viewers, but also key older 18-49 viewers that seem to be shifting allegiances. While "Kimmel" doesn't have any lead in the older viewing groups, he seems to have had impact. "Tonight" is at 990,000 for 18-49 viewers, having dropped 10%; "Kimmel" is at 901,000; and "Late Show" is at 858,000, off 18% from a year ago.