[2][3] The main assumption of the predatory imminence continuum is that as threat levels increase, defensive response strategies change.
However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival.
At this point, the animal enters the circa-strike phase, where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.
[5] Since survival behaviours are so vital for an animal to acquire and demonstrate rapidly, it has been theorized that these defence reactions would not have time to be learned and therefore, must be innate.
[5][6][7] Species-specific defence reactions are now recognized as being organized in a hierarchical system where different behaviours are exhibited, depending on the level of threat experienced.
[3][6] However, when this concept was first proposed, the dominant species-specific defence reaction in a certain context was thought to be controlled by operant conditioning.
[5] That is, if a species-specific defence reaction was unsuccessful in evading or controlling conflict, the hierarchical system would be rearranged because of the punishment, in the form of failure, experienced by an animal.
[8] Other criticisms for this theory focused on the inability for species-specific defence reactions to effectively rearrange in this manner in natural situations.
[7] The rejection of the operant conditioning mechanism for the reorganization of species-specific defence reactions, led to the development of the predatory imminence continuum.
[3] Pre-encounter behaviours can be observed when an animal has left the safety of its residence to perform tasks such as mating or foraging, and occur before a predator has been identified.
[3][10][11] This models the real-life situation of a rat needing to leave the relative safety of its nest to go foraging for food.
The frequency and meal size associated with foraging are reorganized depending on the perceived level of threat but they are not directly influenced by the interaction with a predator.
[3][14] Since the freezing behaviour is dominant in these situations, it can be assumed that it serves an adaptive function by preventing an additional increase in predatory imminence.
[3] If the animal is successful in evading its predator then, when it has found a safe location, it will eventually return to its preferred activity patterns.
[17][18] When rattlesnakes strike, kangaroo rats exhibit a quick and forceful circa-strike behaviour in the form of a leap using their hind legs.
[17][18] If the leap is unsuccessful in completely avoiding the snake's strike, it still serves the purpose of preventing the fangs from embedding.