elapsed is reinforced. While continuous reinforcement in a fixed ratio schedule may be necessary for the initial learning stages, a variable ratio schedule is the most effective at maintaining behavior over long periods of time. There are various methods animal trainers can use to prompt an animal to respond to a stimulus in a specific way. For example, shaping is a process by which successive approximations are rewarded until the desirable response topography is attained. An animal trainer can use conditioned reinforcers, like clickers, to bridge the interval between response and positive reinforcement. Some stimuli that is considered discriminative are signals, targets and cues. They can be used to prompt a response from an animal, and can be changed to other stimuli or faded in magnitude. In order to delay satiation, reinforcer size should be as small as possible and still be effective for reinforcement. Also, the timing of the delivery of a reinforcer is crucial. Initially the interval between response and consequence must be minimal in order for the animal to associate the consequence with the response. Other important issues related to this method are: stimulus control motivating operations Desensitization chaining S-deltas discrimination generalization. Other considerations Certain sub-fields of animal training tend to also have certain philosophies and styles. For example, fields such as: Companion bird training Hunting bird training Companion dog training Show dog training Dressage horse training Mahout elephant training Circus elephant training Zoo elephant training Zoo exotic animal training Marine mammal training The degree of trainer protection from the animal and the tasks trained may also vary. They can range from entertainment, husbandry (veterinary) behaviors, physical labor or athleticism, habituation to averse stimuli, interaction (or non-interaction) with other humans, or even research (sensory, physiological, cognitive). Training also may take into consideration the natural social tendencies of the animal species (or even breed), such as predilections for attention span, food-motivation, dominance hierarchies, aggression, or bonding to individuals (conspecifics as well as humans). Consideration must also be given to practical aspects on the human side such as the ratio of the number of trainers to each animal. In some circumstances one animal may have multiple trainers, in others, a trainer might attend simultaneously to many animals in a training session. Sometimes training is accomplished with a single trainer working individually with a single animal. In some species, the number of trainers is irrelevant, yet it can usually achieve