Which of the following is a legal requirement for Aylmeri jesses?

Aylmeri jesses are specifically designed pieces of equipment used in falconry, and their legal requirement to be used is essential for ensuring the safety and handling of birds of prey. In the context of falconry, using jesses is crucial for managing the bird, allowing for more control and facilitating safe handling when the bird is tethered.

Using jesses is part of established practice within the sport and is critical for the welfare of the bird, helping prevent injuries during training or while in the field. It ensures that the bird can be recalled easily and securely, thus contributing to both the effectiveness of training and the safety of the bird itself.

Regarding the other options: while a GPS tracker and synthetic materials might contribute to the modern version of falconry equipment, they are not universally mandated for Aylmeri jesses. Similarly, while a special harness might be used in certain situations, it is not a legal requirement for all falconers. Therefore, the use of Aylmeri jesses is the legal necessity that directly relates to practice in falconry.