Dwindling food sources are forcing thousands of pink-footed geese to feed on farm crops instead during their winter visits to Norfolk, said a leading farm conservationist.
The county hosts a third of the world's population of the migrating birds at this time of year, providing one of the region's great wildlife spectacles along the coast.
They enjoy eating sugar beet tops and will graze on harvested fields for up to 30 days after the crop has been gathered.
But modern farming methods are among the main reasons the birds are "running out of food", said David Lyles, an award-winning farm conservationist based at Muckleton near Burnham Market, who is also a director of the National Nature Reserve at the Holkham Estate.
Mr Lyles said the causes of the problem include the ploughing of sugar beet fields immediately after harvest to plant winter wheat crops, and the increased efficiency of harvesting machines to pulverise beet tops, resulting in little or no residue for feed.
He warned that a lack of available food will cause the birds to "transgress onto unharvested sugar beet" as well as other crops such as oilseed rape and cereals - and this new habit would quickly be learned by new generations.
"Norfolk hosts nearly a third of the world population of these geese and we therefore have a responsibility to act," he said.
"We cannot wait as the problem is becoming more acute. We need and a county-wide discussion with farmers, wildlife conservation bodies, the leisure industry and government to debate the best way forward."
Mr Lyles hopes to spark a debate on potential solutions which could include encouraging farmers to avoid ploughing in sugar beet tops directly after harvest, perhaps funded as part of the government's new Environmental Land Management Scheme (ELMS) currently under development to replace the EU's subsidy system after Brexit.
He also suggested changing the settings on harvesters to provide less mulched top and residue, adding: "I have spoken with people selling machines and this should be possible - in the extreme need and with the right incentives more friendly toppers could be designed."
Mr Lyles also urged well-meaning bird-watchers to try to avoid being seen or disturbing the geese while they are feeding on harvested sugar beet fields, to prevent moving them onto other crops.
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