Behavioral Aspects of Feigned Death in the Opossum Didelphis marsupialis

Abstract

Behavioral aspects of feigned death were studied in captured opossums (Didelphis marsupialis). Feigned death was induced by grabbing and shaking the opossums by predators (either human or dogs). It is a stereotyped behavior pattern characterized by a ventral flexure of the body, flexure of the digits, and grasping of lhe substrate. The opossum lies on its side with its feet visible. Corncrs of the mouth are retracted initially and then usually relaxed. The eyes remain open. During sleep, in contrast, the opossum keeps the mouth and eyes closed and its dorsum uppermost with the feet out of sight. Sham attacks rarely caused opossums to feign death; almost invariably tactile stimula- tion (grabbing) was necessary. Opossums feigning death may twitch the ears at sharp noises, retract the lips when prodded, or claw the air when picked up by the tail. Opossums raised in cages could not be induced to feign death even by grabbing. But when females with pouch young were captured and kept in a large indoor enclosure, their young showed the ability to feign death at 120 days of age. The feigned death response develops near the time of weaning. When six animals were stimulated daily, all continued to feign death for at least 12 days and one was still responding at 60 days. Generally the duration of feigned death increased with daily stimulation. Adult opossums responded less readily than ones under 8 months of age.