A jess (plural "jesses") is a thin strap, traditionally made from leather, used to tether a hawk, falcon, or owl in falconry.[1] Jesses allow a falconer to keep control of a bird while it is on the glove or in training, and allow a bird to be secured on a perch outside its aviary.[1]
Jesses come in various types:
Jesses are generally made from strips of leather as thin as possible, for which purpose kangaroo leather has become increasingly popular over the years, as it is thin, light-weight and extremely durable with proper care. Jess size varies depending on the bird, but the width is proportional to leg-length. Traditional jesses are made from a single length of leather, and slits are placed strategically along the jess to allow it to be looped through itself and around the ankle of the bird so that it fits comfortably but securely about and just above what would be the bird's ankle. With Aylmeri jesses, as created by Major Guy Aylmeri, the end of the jess is instead looped through itself repeatedly to form a "button", or knob at one end. The thin, pliable end of the jess is then threaded through an anklet worn by the bird, which is itself formed of another rectangular strip of leather, bound together at the ends by a grommet (usually of brass), prevented from slipping through the grommet by the knobbed end. Often, another slit is placed near the thin end of the jess cut about one inch long and running lengthwise, through which a special type of swivel is fitted, preventing the whole arrangement from twisting or tangling about itself or the bird when a leash is threaded through the other end.
Their intent is more to prevent the risk of the bird deciding to chase something it shouldn't, and less to keep the bird from getting away, as falconry birds are routinely (and as part of the sport) set free—the bond between bird and falconer serves as a much better leash than any leather or rope ever will; however, it is not always desirable that a bird be able to take flight at its own whim, and both on the glove and on the perch, jesses help ensure this.
During hunting season (small game season for North American falconers), jesses are generally worn all season in the mews, and are often removed for the course of the spring/summer moult, when they are generally re-oiled and serviced as necessary.