The top four networks collectively are down 17% in Nielsen-measured average prime-time viewers and 23% in average prime-time 18-49 viewers.
Looking specifically at each network, CBS is 22% lower (to 5.6 million viewers), while NBC is down 20% (to 5.0 million), ABC has lost 13% (4.5 million); and Fox is 10% less (4.2 million).
For the 18-49 viewing metric that major TV advertisers still closely watch, the overall data trend is worse, with Fox sinking 12% to 1.43 million viewers, NBC 28% lower to 1.24 million, ABC 21% lower to 1.17 million and CBS 32% lower to 1.0 million.
Nielsen results come from live program-plus-seven days of time-shifted viewing from January through November and for the most recent two weeks, live program-plus-same day time-shifted viewing through December 13.
Big TV networks -- especially since the start of the traditional TV season in late September -- have suffered from delays in production of TV prime-time shows.
At the same time, the next five of six TV networks -- completing the top-ten U.S. viewing networks -- showed gains, especially cable TV news networks, due to election and pandemic coverage.
Fox News Channel was up 45% to 3.6 million, while MSNBC added 23% to 2.1 million, CNN was 84% higher to 1.8 million, Univision added 11% to 1.45 million and TLC was up 16% to 1.37 million.
Sitting in eighth place is ESPN, down 17% to 1.46 million.
The network, and other sports channels, had no live sport TV programming for months due to cancellation of major sports leagues and associations -- including the NBA, NHL, Major League Baseball, and PGA Golf.
NBCSN (NBC Sports Network) and Fox Sports 1 were each down 26% to 250,000 and 236,000 respectively, in average prime-time viewers.