Expanding an airport next to a Kent nature reserve which is a magnet for tens of thousands of birds could put flights in danger, a report has said.
Dungeness has tens of thousands of birds, the RSPB has said
The study by a Leeds University professor was commissioned by the RSPB, which is opposing the expansion of London Ashford Airport (LAA) in Lydd.
Professor Chris Feare was asked to look at bird-hazard control at the airport.
But LAA chief Zaher Deir said it had been proven birds and aviation could co-exist in the same surroundings.
Professor Feare's report said the proposals for an extended runway and new passenger terminal could pose an "extremely hazardous" bird-strike threat.
And he said pilots may need to exercise considerable flexibility to avoid putting their flights in danger.
He recommended measures to be taken at the airport to minimise risk, such as netting ponds and lakes, and preventing birds nesting in aircraft hangars and on roofs.
Airport planners want a longer runway and new terminal building
RSPB chief Graham Wynne said the report proved expansion was "a non-starter".
He said the 75-year-old, 1,000-acre Dungeness reserve had up to 120,000 birds in the winter, and more than 60 breeding species in the summer.
Concerns raised by the RSPB are that larger planes could harm birds and other wildlife, with disturbance and pollution.
Mr Deir said: "It is not the number of passengers that matters, it is the effective management of bird-control systems around any airport that really counts."
He said the findings of three bird surveys had been submitted to Shepway Council, which will consider the plans this month.