Fear bradycardia in free-ranging woodchucks, Marmota monax. [Bradycardie de peur chez les marmottes sauvages (M. monax)].

Résumé

The classic response to fear is increased heart rate and an overall readiness for "flight to flight". Sympathetic activity increases and the animal is generally prepared for stress (Grinnel, 1977). Alternately, an animal may respond to danger by passively "hiding and freezing"; the latter response often results in bradychardia. Telemetrically measured heart rate from a free-ranging submerged alligator; Alligator mississippiensis, dropped from bpm to less than 2 bpm when frightened (Smith et al. 1974). Gabrielsen et al., (1977)reproted a 30% reduction of heart rate when telemetered, incubating willow grouse, Lagopus lagopus, were approached by man or dog. Jacobsen (1979) reproted a ean reduction in heart rate of 38% when white-tailed deer, Odocoileus virginianus, fawns responded to stimuli by "freezing". Smith and Worth (in press) recorded a mean heart rate reduction of 25% during fear bradycardia in estern cottontail rabbits, Sylvilagus floridanus, that could not be abolished with atropine treatment. Free-ranging Uinta ground squirrels, Spermophilus armatus, showed a reduction in heart rate of 100 bpm when approached by an (Ruff, 1971). Edgard Folk, Universityof Iowa Medical School, observed fear bradycardia in active woodchucks and distrubanc tachycardia in hibernating woodchuck (pers; comm.). Woodchucks are large fossorial rodents that live in extensive burrows (Grizzel, 1955; Merriam, 1966; Hayes, 1976). Cardiovascular response to hypoxia and oxygen affinities were described (Hall, 1965; Burlington et al., 1971).