Up to 600 pigs are expected for this year's pannage season
Hundreds of pigs are roaming free in the New Forest National Park munching their way through a glut of acorns which are toxic to the wild ponies.
Verderer Colin Draper said: "A dozen animals or more die because they've eaten too many acorns, it affects their livers and they die a painful death."
Every autumn commoners turn their pigs out to eat the acorns in an ancient right known as the pannage season.
Normally 300 pigs are left to graze but this year up to 600 are expected.
The thousands of oak trees in the 141,097 acre (571 sq km) national park have an unusually full crop of acorns this September.
"We had thought because it was such a dry summer that the acorns would be smaller and the crop would be less significant," Mr Draper said.
"In fact it's quite the reverse. We've got enormous acorns," he added.
They're falling early and it is a concern for people with ponies and cattle, but they are a marvellous food for pigs."
Although they appear to be wild, all the cattle, ponies and pigs in the New Forest are owned by the forest's 400 commoners.
The commoners have the right to graze their livestock on the open forest. They pay a token fee for each pig they turn out to forage on the crop.