Death Feigning by Ducks in Response to Predation by Red Foxes (Vulpes fulva)

Abstract

Predation by captive red foxes (Vulpes fulva) on approximately 50 ducks comprised of five species was observed in tests conducted at the Northern Prairie Wildlife Research Center, Jamestown, North Dakota. Most ducks were attacked from a rear or lateral position and seized in the cervical or thoracic region. All birds became immobile (death-feigned) immediately when seized and with few exceptio'ns remained motionless during prey-handling and for varying lengths of time thereafter. Initial death feints lasted from 20 sec to 14 min. Recovery was delayed by tactile, visual and, possibly, auditory cues from the foxes. Death-feigning birds appeared alert and often took advantage of escape opportunities. Twenty-nine birds survived initial capture and handling by the foxes. Naive foxes were wary of ducks during initial confrontations, but experienced foxes showed little hesitation in attacking them. After capture, most ducks were taken alive to, lay-down sites where they were mouthed and often killed. Then the ducks were usually cached or taken to, dens or pups. Several birds were cached alive. Red foxes appear to have adapted to the escape of death-feigning ducks by learning to kill some birds soon after capture and by the evolution of an appendage-severing behavior. Death feigning appears to be a highly developed antipredator behavior of ducks that facilitates the escape of some birds after capture by red foxes. INTRODUCTION The so-called immobility or hypnotic reaction of animals was first described in the mid-1600's (Gilman and Marcuse, 1949), and since then the phenomenon has been observed in many species (Armstrong, 1965; Ratner, 1967). Among vertebrates, the reaction has been studied most intensively in birds; Armstrong (1965) cites examples of immobility in over 20 species. Perry (1938, p. 142-143) described the reaction of a wild eider drake , presumably a common eider (Somateria moltissima), that became motionless as if he were dead . when handled. have been numerous theoretical explanations of the immobility reaction, including hypnosis, reflex response and cerebral inhibition, sleep, spatial disorientation, paralysis of fear and death feigning (see review by Ratner, 1967). Evidence is mounting, however, that such a reaction is an innate fear response that serves as a defense against predators (Gallup, 1972; Gallup et al., 1972; Gallup et al., 1971a; Gallup et al., 1971b; Ratner, 1967). Several studies have shown that predators may elicit immobility reactions among prey (Francq, 1969; Gallup et al., 1971a); however, Gilman et al. (1950, p. 110) stated, There is little real evidence to show that dead animals, or animals who appear dead, will not be eaten by preying ones. Others have suggested that immobility may serve to minimize stimulation for further attack (Gallup, et al., 1971a) or that