FACULTATIVE TORPOR IN FREE-RANGING BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS)

Although facultative torpor has been observed in laboratory populations of black-tailed prairie dogs (Cynomys ludovicianus), it is widely believed that these animals remain normothermic throughout winter in the field. We monitored body temperatures (Tb) of 5 black-tailed prairie dogs in the field for about 100 days during winter and spring 1998–1999. All animals entered torpor during this period. Major torpor bouts averaged 140.5 h ± 2.4 SD (range = 77.6–214.4) with a minimum Tb of 19.0 ± 3.6°C. Minor torpor bouts averaged 46.2 ± 20.9 h (9.5–98.5), with minimum Tb reaching 30.3 ± 2.3°C. There was no distinct relationship between ambient air temperature (Ta) and entry into torpor. All torpor bouts occurred following a sudden reduction in Ta, but not all sudden reductions in Ta induced torpor. Precipitation was not associated with entry into or arousal from torpor. Our study demonstrates that facultative torpor occurs in free-ranging black-tailed prairie dogs in the field.