Purple Martin Preservation Alliance
Here are some photos of a squirrel climbing a metal martin pole and gaining access to the martin house. Squirrels are a potential martin predator; they will eat eggs and young. Notice how the squirrel is agile enough to get from the pole to the house. Raccoons are similarly agile, and, just like squirrels, they climb by "hugging" the pole, which means even smooth metal poles are easily climbed.
These photographs were taken by D. Trinter, a martin landlord in OH.