What is missing on 907's leg?

Matt Strausser of the ICF Tracking Team took these photos of #907 at the Chass pen, saying: "In one, #907 is missing her PTT statelite transmitter. We had to remove, repair, and reattach it to ensure that it was functioning properly. Our senior project biologist from US Fish and Wildlife, Dr. Richard Urbanek, fixed it. Crane 907's satelite transmitter is now working quite well and shows that she is still here at Chass on the morning of 3/25."