Great Yarmouth Air Show: Red Arrows disturbed birds
BBCAn RAF Red Arrows display at an air show "caused the greatest disturbance" to nesting birds despite the flight path being changed, the RSPB said.
The two-day festival took place in Great Yarmouth for the first time in June - but organisers had to make changes to avoid affecting little tern colonies.
The RSPB said its monitoring showed the birds were still disturbed.
The air show organisers have yet to comment.
Jeff Knott, the RSPB's regional director for Eastern England, said its initial concerns were justified: "RSPB monitoring of the colony during the air show this year revealed that Red Arrow fly-pasts caused the greatest disturbance to nesting little terns.
"In addition, the parachute display and other activities held over 1km away were observed to have disturbed all the terns on Scroby Sands.
"Any future air show events during the summer will put these colonies of nesting little terns at further risk - particularly if they include displays by the Red Arrows, " he added.
In May, the organisers said they had made adjustments to the flight path of the Red Arrows to give the colonies a wider berth.
RSPBThe charity says 20% of the entire UK little tern population is in East Norfolk, and that the were among the UK's rarest sea birds.
It says if they are disturbed, the birds may go away from their nests, leaving the eggs unprotected, or the terns may not feed their young as often as normal.
About 180,000 people attended the free show, but figures seen by the BBC show it made a £500,000 loss.
The tourism and business improvement board said it hoped the festival, in some form, would return in 2019.