Without fundamental changes in farming and radical improvements in port surveillance, we remain at high risk of new disease outbreaks every day.

BBC: The pointless slaughter?

The prince, referring to changes in farming with the reform of the Common Agricultural Policy, said the emphasis would be on quality, not quantity.

BBC: NEWS | UK | Wales | Mid | Prince urges school cooking lessons

Another theory is that the birds may have fallen victim to hunting, development or changes in farming along their 6, 000km (3, 600 mile) migration route to breeding grounds in the Russian Arctic.

BBC: Red-breasted goose

Researchers addressing the British Association's science festival in Leicester last month said a new directive from Brussels could lead to radical changes in the way agricultural land was managed across Europe, with some types of farming being scaled back or even abandoned in some of their traditional areas.

BBC: English and Welsh rivers 'improving'