My thoughts are that it would not be OK to deliberately prevent any animal for reaching sanctuary if it wishes to do so. I could understand if it happened inadvertently but if it is deliberate, this is a negative interaction.
I am interested to hear that the D500 and Sigma 8-16mm appear incompatible. This is actually pretty rare. Could it be a malfunction with the individual camera or lens?
The 11-16mm is akin testing focal length. Effectively, it is a 16-24mm on a full frame and i shoot quite a lot with the 16-35mm. The key will be whether the corners will work.
I've used the Tokina 10-17mm with a TC for CFWA in the past and it works well for that. It still produces lots of barrel distortion though. I actually quite like the distortion, unless there are obvious straight lines in the scene.