The National Football League's viewership declined 2% this season, weighed down by a smaller audience for Thursday night games that moved exclusively from broadcast TV to Amazon's Prime Video.

"Thursday Night Football" on Prime Video averaged 9.6 million viewers. That was down about 40% from the 16.4 million viewers who watched Thursday games on Fox, the NFL Network and Prime Video last year. Amazon's audience was down about 30% when including four stand-alone games last year on the NFL Network and excluding a highly rated Christmas Day game last year.

Across all its broadcasters, the NFL's regular season games averaged 16.7 million viewers, compared with 17.1 million viewers last year.

Few industry observers expected Amazon to reach as large an audience as traditional TV networks, which have broad distribution and fans accustomed to watching them. The ratings decline still raises questions of whether sports leagues are sacrificing viewers when selling media rights exclusively to streaming services.

Despite the decline, the NFL remains the most popular programming on TV. This season, NFL games made up 47 of the top 50 telecasts.

This season, Amazon began an 11-year, $13 billion deal that made it the exclusive home of "Thursday Night Football." Amazon had streamed NFL Thursday games in the past that also aired on the NFL Network and Fox. But it had never had an NFL package to itself.

About 80 million households have watched Prime Video at least once in the past year. That's about the same number who subscribe to a pay TV service. But Amazon faced the challenge of making sure fans would be able to find the games on a streaming app instead of traditional TV. And ratings can depend on how competitive the games are.

Amazon's viewership fell short of the roughly 12 million people that it had promised advertisers that they would reach. When that happens, broadcasters typically offer advertisers free commercial time on other programs to make up for the shortfall.

"We worked closely with our advertising partners throughout the season to deliver on our commitments, and we look forward to creating even more opportunities and innovations next season," Amazon said in a statement.

Amazon said it averaged 11.3 million viewers, according to its own data, and reached more viewers in the younger demographic than last year when the Thursday games were on regular TV.

"We are only at the beginning of a long-term mission, but are ecstatic with the results and achievements of this first season, bringing millions of viewers to Prime Video every week," said Jay Marine, Amazon's global head of sports.

Other NFL broadcasters saw increases. Fox averaged 19.4 million viewers, a 4% lift. NBC's Sunday night games drew 19.9 million viewers, up 3%. CBS said its 18.5 million average viewers made it the network's most watched regular season in seven years.

ESPN's "Monday Night Football" audience fell 3% to 13.8 million. The network's ratings were hurt, in part, by the exclusion of the game between the Buffalo Bills and Cincinnati Bengals that was canceled after a harrowing injury to Bills player Damar Hamlin.