The phrase “un peu de croyance” is French and oughly translates to “a little bit of belief” or “a little bit of faith”. In the context of training a hawk, it refers to the measure of trust and confidence that the trainer needs to have in the hawk in order to train it.
Somehow or other croyance becomes creance, and the phrase becomes un peu de creance. Creance means debt in modern French.
The idea though is that until the bird is trained, the trainer has only a little faith that the bird will return, so in the training period the trainer uses a creance.
A creance is a long, light cord used to tether a flying hawk or falcon during training.
The creance itself is about 80 feet long, and designed to be of as little inconvenience to the bird as possible, and hardly noticeable.
Eventually, when the trainer knows the hawk will return, he removes the creance during flights.