Jess (falconry) 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
Falconry supposedly appropriate. This list, however, was mistaken in several respects. It can be seen that the relevance of the "Boke" to practical falconry past or present is extremely tenuous, and veteran British falconer Phillip Glasier dismissed it as "merely a formalised and rather fanciful listing of birds". A book about falconry published in 1973 says: There are several raptors used in falconry. They are typically classed as follows: Owls are also used, although they are far less common. In determining whether a species can or should be used for falconry, the species' behavior in a captive environment, its responsiveness to