The ratings slide coincides with changes to TV3's Sunday night schedule, which saw it move to a reduced half-hour news bulletin, ahead of the weekly current affairs programme 3D.
The new format debuted on May 24 to reasonable ratings, but viewers have failed to stay with the line-up. Last night's episode of 3D saw just 160,000 viewers tune in.
Gillman says it's possible some viewers have tuned out following MediaWorks' decision to axe Campbell Live and the company's perceived lack of commitment to current affairs.
"MediaWorks obviously feel comfortable experimenting but they've had too many failures lately. They'll be thinking long and hard about what to do now."
Meanwhile, TVNZ's One News drew a massive 802,000 viewers last night, making it one of the year's top rating shows.
Traditionally, Sunday night delivers the highest viewership figures, making last night's loss even more concerning. However, Gillman warns against looking at just one day's figures.
"They have a broader issue around their news ratings. Yesterday was a low point for them but it's definitely an ongoing problem."
Ironically, Prime News' ratings success comes after MediaWorks took over production of the bulletin in March.
The numbers*
Last night:
3 News: 166,210
3D: 159,960
One News: 802,400
Prime News: 178,600
May 31:
3 News: 212,640
3D: 211,970
One News: 640,220
Prime News: 164,450
May 24:
3 News: 313,520
3D: 212,060
One News: 805,820
Prime News: 184,140
*National, 5+
- nzherald.co.nz