While special events are doing well for broadcasters -- capped off by an Oscars telecast that was the most-watched entertainment program in five years -- their day-to-day schedules are hurting.

The Nielsen Co. said Tuesday that 41.7 million people watched the Academy Awards on ABC on Sunday. People are flocking to awards shows and sports. Last month, the Super Bowl set an all-time viewership record, and the Grammy Awards' audience was 36 percent larger than the year before.

Yet of the 20 most popular returning prime-time series, 16 have smaller audiences than they had last season to this point, Nielsen said. "CSI," once TV's most popular program, is down 22 percent.

Experts have suggested that social media have helped drive the popularity of special events, with viewers commenting on awards shows via Twitter or Facebook while watching. People are less likely to do that with the 12th episode of a sitcom's 22-episode season.

Bucking the trend most prominently is the CBS comedy "The Big Bang Theory." The show's average audience is 12.9 million this season, up from 9.6 million at the same time last year. TV's most popular scripted drama, "NCIS," also is continuing to grow.

Two of the 20 most popular shows this season, CBS' "NCIS: Los Angeles" and "Undercover Boss," are new. Otherwise, 18 of the 20 most popular returning shows have been on the air since 2005 and earlier. "Survivor" is in its 20th cycle, "American Idol" in its ninth and "The Amazing Race" in its 16th.

 1 Academy Awards (ABC)

2 Oscar's Red Carpet (ABC)

3 American Idol, Wed. (Fox)

4 American Idol, Tue. (Fox)

5 NCIS (CBS)

6 American Idol, Thu. (Fox)

7 Two and a Half Men (CBS)

8 The Big Bang Theory (CBS)

9 CSI (CBS)

10 The Bachelor (ABC)

11 Barbara Walters Special (ABC)

12 The Mentalist (CBS)

13 NCIS: Los Angeles (CBS)

14 The Bachelor: After the Final Rose (ABC)

15 The Good Wife (CBS)

16 Criminal Minds (CBS)

17 Survivor: Heroes and Villains (CBS)

18 CSI: NY (CBS)

19 CSI: Miami (CBS)

20 Grey's Anatomy (ABC)