Historical preservationists in southwest England have just one question for the birds that are tormenting them: Why?

OK, two questions: Could they stop, please?

Jackdaws — small birds in the crow family that are common in the U.K. — have been tearing apart the roof of a historic thatched barn in Avebury, Wiltshire. The Tithe Barn, owned by the U.K.'s National Trust, is home to a museum dedicated to the Avebury Henge.

Three years ago, the National Trust raised money to re-thatch two-thirds of the roof. The BBC reports that the total cost was £100,000.

The project was a great success — for six months. Then the jackdaws swooped in.

Ever since, the birds have been steadily pulling pieces of straw out of the roof — and "idly discarding them," as the National Trust put it in a statement.

"We don't know why they are doing this," Karl Papierz, the National Trust's building surveyor for Avebury, said in the statement.

The birds don't seem to be finding any food in the roof, Papierz noted. And while a few pieces of straw are used in nests, he said, "most is simply pulled and discarded."

"They even pile it up to make a ledge they can use to stand on and pull out more."

Master thatcher Ed Coney, who worked on the roof restoration project, was quoted by the BBC as saying it was "soul-destroying" to watch his handiwork pulled apart.

NPR attempted to speak with Coney, but at the time this piece was written, he was "perched on top of a roof," as he put it, and unavailable for comment.

Papierz, the building surveyor, says the National Trust has tried method after method of deterring the birds, to no avail.

Coating the thatch? Mounting wooden falcons? Installing spinning decoys? Laying netting over the thatch to block the birds? Removing netting so the birds don't have a foothold?

The birds have figured out a way around every method.

"While we win for a period of time, the jackdaws eventually come back and start pulling straw again," Papierz said. "It is very frustrating."

"Jackdaws are very clever birds," he said.

If you're thinking there's a straightforward solution to the problem — one that involves firearms, perhaps — think again. Jackdaws, like other members of the crow family, are protected animals in the U.K., and permits to kill or trap them can only be granted to prevent serious damage to crops, livestock, public health or other wild birds.

The Tithe Barn isn't the only building where jackdaws have wreaked havoc on the roof, with no apparent benefit to themselves — but it's not a problem for every thatched building.

The arbitrariness with which birds pick such targets is apparently a source of frustration for building owners: The U.K.'s Thatch Advice Center writes, "We know about birds attacking roofs. ... How many times have we heard someone say — why my roof and not the one next door, they were both thatched at a similar time?"

The site offers no answer.

For now, Coney, the master thatcher, is working with the National Trust to set up a new deterrent: netting suspended above the roof on metal supports.

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