The Casa Grande Ruins National Monument in Arizona is dealing some unusual threats: birds and squirrels.

Pigeons and other birds have been and building nests and pecking at the site's structures, which date back several hundred years. Squirrels have dug tunnels throughout the 472-acre complex, weakening some of the most important buildings.

Paige Baker, the monument's superintendent, says the buildings will worsen unless the issue is addressed. Development around the park is also causing problems.

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Prehistoric Site Under Attack by Birds (AP 1/18)
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Casa Grande Ruins National Monument - http://www.nps.gov/cagr

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