Motivational Systems of Agonistic Behavior in Muroid Rodents
Motor Patterns of Defense Page 13



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Several motor patterns of defense (usually found in only a few muroid rodent species) may have evolved because they enhance the visibility, apparent size, and effectiveness of defense motor patterns. These include piloerection, tail-raising, and cheek-pouch inflation. Although piloerection is confined to offense in most muroid rodent species, it is associated with defense as well in L lemmus [Arvola et al, 1962]. The unusual use of piloerection during defense in this species is associated with other unusual aspects of defense including bright hair-color patterns and frequent use of lunge-and-bite attack against predators, all of which may be considered a case of aposematic defense [Andersson, 1976]. Tail-raising by the defensive animal during conspecific fighting has been reported in Mi agrestis [Clarke, 1956], Me auratus [Shipley and Kolb, 1977], P califo!nicus and maniculatus [Eisenberg, 1962], O irroratus [Davis, 1972], Mi ochrogaster and pennsylvanicus [Getz, 1962], and Mer unguiculatus [Swanson, 1974]. Cheek-pouch inflation has been reported to accompany the defensive upright posture in Cr gambianus [Ewer, 1967] and Cricetus cricetus [Eibl-Eibesfeldt, 1953a] .

Squealing vocalization is practically universal during defense among the muroid rodents. In laboratory species it is routinely recorded during fighting or in response to rough handling or pain. In other species it is noted from the defensive animal during fighting and called a variety of names: Voiced cries in L lemmus [Arvola et al, 1962]; squeals in R villosissimus [Begg, 1975]; squeals, squawks, and grinds in D groenlandicus [Brooks and Banks, 1973]; squealing in Mi agrestis [Clarke, 1956]; chit vocalization during fighting and alarm squeal when restrained in O irroratus [Davis, 1972]; protest squeak in Cr gambianus [Ewer, 1967]; shrill squeaking in R rattus [Ewer, 1971]; graded series of squeaks ranging from prolonged squeaks to the sharp, explosive "chit" in association with the lunge-and-bite in Peromyscus sp var [Eisenberg, 1962]; squealing in Clethrionomys sp var [Johst, 1967]; shrill squeal of rage and distress squeals in Ne fuscipes [Linsdale and Tevis, 1951, p 233]; squeaking in N alexis [Stanley, 1971]; and sharp cries ("reskie kriki") in Rh opimus [Goltzman et al, 1977]. A number of investigators note that the squeal is modified in association with a lunge-and-bite attack into a sharper, more explosive sound which is timed to coincide with the lunge.

In some species, a squeal is given when a potential predator is still at some distance from the animal, ie, beyond Hediger's "flight distance." It has been speculated that the behavior, in this case, serves as a warning signal to conspecifics, eg, in Mi brandti [Reichstein, 1962]; Rh opimus [Naumov, 1975]; and in D groenlandicus [Brooks and Banks, 1973]. It is not clear if these apparent alarm calls are actually different motor patterns from other squeals, or it they are the same motor pattern with a lower threshold of elicitation, ie, at a threshold which is reached before flight distance is breached by the stimulus animal.

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