Those twist ties are very soft, even for aluminum, to make them easier to twist around the fencing, and a squirrel's teeth are very tough. As for why they choose them, that's a good question. I have a customer whose AC units have been victimized by squirrels. They have chewed through the low-voltage wiring several times, costing thousands in repairs. The customer initially used traps, and relocated the squirrels a short distance away. I told them the squirrels were probably beating them back to the business, and convinced them a more permanent solution was in order. I was actually thinking they would still use traps, but hey now discretely end the squirrels' reign of terror with a break barrel air rifle. I'm making less money there now, but it's all good!
