A creance is a long light cord used to tether a flying hawk

Hawk

The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...

 or falcon

Falcon

A falcon is any species of raptor in the genus Falco. The genus contains 37 species, widely distributed throughout Europe, Asia, and North America....

 during training in falconry

Falconry

Falconry is "the taking of wild quarry in its natural state and habitat by means of a trained raptor". There are two traditional terms used to describe a person involved in falconry: a falconer flies a falcon; an austringer flies a hawk or an eagle...

. They are used both when the bird is young, and when the bird has been taken out of the aviary for a moult or other reasons.

The creance itself is thin, designed to be of as little inconvenience to the bird as possible. It's threaded through the swivel

Swivel

A swivel is a connection that allows the connected object, such as a gun or chair, to rotate horizontally and/or vertically. A common design for a swivel is a cylindrical rod that can turn freely within a support structure. The rod is usually prevented from slipping out by a nut, washer or...

 and tied with a falconer's knot

Falconer's knot

The falconer's knot is a knot used in falconry to tether a bird of prey to a perch. Some sources show this knot to be identical to the halter hitch, but with a specific method of single-handed tying needed when the other hand is occupied holding the bird....

. The creance typically extends to around 25 metres (82 feet), at which point the bird should be ready to fly free (without the use of the creance).