Motivational Systems of Agonistic Behavior in Muroid Rodents
Motor Patterns of Defense Page 11



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Freezing is usually the initial defense response by wild muroid rodents to stimuli associated with a predator. Only when the potential predator approaches to within a critical distance does the defensive animal change from freezing to other defense behaviors such as flight or threat and/or lunge-and-bite [Hediger, 1934]. Freezing in response to a distant predator has been described for M musculus in response to owls [Payne, 1971], P leucopus and Mer libycus in response to owls [Lay, 1974], and C glareolus, Mi agrestis, and A sylvaticus in response to weasels [Erlinge, 1975] .Several species of these genera have also been shown to freeze in response to stimuli which mimic an aerial predator [Fentress, 1968; Rosenmann and Morrison, 1975]. The laboratory rat, R norvegicus, characteristically freezes in a crouching position in response to a dog or cat [Blanchard et al, 1975b].

Freezing may also be employed by muroid rodents after they have been captured and are within the grasp of a predator. Leyhausen [1973] describes a case in which a golden hamster [Me auratus] lay immobile on its back after being attacked by a civet cat, and was not attacked until it rolled onto its feet and tried to crawl away. The behavior of "feigning death" when grasped by a predator has been reported in many different vertebrates [Ratner, 1975]; it is presumably responsible for the tendency of some muroid rodents to remain immobile when grasped by the experimenter, eg, in Tatera leucogaster [Choate, 1972], and P leucopus and maniculatus [Vestal, 1975].

Flight, as a response to a predator, or as a response to a conspecific attacker, is presumably present in all muroid rodents. Detailed descriptions have been made of aspects of flight for R rattus [Ewer, 1971], A sylvaticus [Bovet, 1972], P polionotus [Blair, 1951], various Peromyscus sp [Eisenberg, 1968; Smith and Speller, 1970], M musculus [Crowcroft, 1966, pp 13-15], and R norvegicus [Calhoun, 1962, p 181].

The initial movement of flight has been modified in many species into an "escape leap." In some species it accompanies anatomical specialization of the hind limbs for leaping, eg, Mer unguiculatus [Swanson, 1974], Mer libycus [Lay, 1974], and N alexis [Stanley, 1971]. In species of Peromyscus it may be elaborated into a backwards somersault [McCabe and Blanchard, 1950] . Escape leaps have also been reported in R rattus [Ewer, 1971], Mi pennsylvanicus and ochrogaster [Krebs, 1970], Mi pinctorum [Novak and Getz, 1969], and Rh opimus [Goltzman et al, 1977].

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