The danger of birds being sucked into aircraft engines could ground Boris Johnson's estuary airport dream.
Bird strikes, as they are known, have brought down at least 108 planes, killing 276 people, since civil aviation began.
The danger posed by the huge bird population at the mouth of the Thames has now been identified as a major stumbling block for plans to build a new airport at the site, as backed by Boris Johnson.
It is one of several potential pitfalls cited in a series of feasibility studies into the new airport, which would see Heathrow transformed into a new London borough, with up to 150,000 homes.
A report by consultancy firm Leigh Fisher warns of an 'elevated bird strike risk' if the airport gets the go-ahead.
Although it concludes the problems are 'not insurmountable', the study suggests overcoming them will have a significant ecological impact.
Another report, by Jacobs, puts the cost of rehousing displaced wildlife at up to £2 billion. It also suggests the airport's backers would need to prove there were no 'feasible alternative solutions' in order to justify the loss of habitat.
The studies were carried out by three independent consultants for the Airports Commission, which is assessing the case for aviation expansion in the UK.
As well as evaluating the environmental impact, they examine the economic case for a new airport.
It must now decide whether a Thames estuary airport merits further consideration or should be consigned to the scrapheap.
Bird strikes: what you need to know
* The first recorded human death from a bird strike was in 1912
* Bird strikes are known to have brought down at least 108 planes, killing 276 people
* Bird strike damage is estimated to cost up to $391m a year in the US alone
* Flight delays and cancellations caused by bird strikes globally are estimated to cost the aviation industry at least $1.2bn a year
* Probably the most famous bird strike happened in 2009, when a flock of Canada geese caused a US Airways pilot to make an emergency landing in New York's Hudson River