Local archaeologist Andrew Fitzpatrick of Wessex Archaeology says burial mounds with ancient human remains are especially sensitive to burrowing animals.
"A Bronze Age burial mound can look quite well preserved, but inside the animals can be causing a lot of damage," he said.
"As they burrow, they destroy the archaeological evidence. It's like putting it through a mixer," Fitzpatrick said.
"Once it's been scrambled up, it really loses a huge amount of its value," he said.
The survey highlighted Offa's Dyke, a massive defense built along the Welsh border by an eighth-century Anglo-Saxon king.
The 80-mile-long (128-kilometer-long) earthwork is rapidly turning into a "Swiss cheese" because of tunneling badgers, according to Chris Martin of the Clwyd-Powys Archaeological Trust in Wales.
A big increase in burrowing activity has been recorded in the last 10 to 20 years, Martin said.
Established badger burrows or rabbit warrens tend to move along the earthwork, Martin said.
"This destroys archaeological deposits in the layers within the dyke and can make it quite dangerous," he said.
The badger holes have also become a hazard to both people and livestock, he said.
"Ultimately if you've got enough big holes in a particular section, it will disappear, because the structure will start to collapse," Martin added.
Protecting Sites From Protected Species
So far there's no clear solution to save the bigger sites.
While it is possible to move the protected badgers under strict license from wildlife authorities, this would not be practical for a monument the size of Offa's Dyke, Martin said.
"If you move them from one location, they may simply go a hundred yards (90 meters) up the road," he said.
Nor, according to Martin, would fencing out burrowing animals be practical: "We certainly couldn't afford 80 miles (130 kilometers) of chicken wire."
English Heritage's Chadburn agreed such measures would not work for large sites like hill forts, but she says a pilot protection project on Salisbury Plain is giving hope for smaller monuments.
Strong metal meshes placed at around 20 sites seem to be effective, she said.
"You can lay them over the site—almost like a carpet—so the grass grows through and there aren't any unsightly fences," Chadburn said.
Mesh coverings are expensive but cost effective in the long run, she said. The coverings should last about 30 years.
The report, called Heritage at Risk, found that, overall, one in 12 of England's protected heritage sites is at high risk from a range of threats, including burrowing, scrub and tree growth, vandalism, and neglect.
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