Nocturnal hypothermia in fasting Japanese quail: the effect of ambient temperature

Japanese quail were equipped with intraperitoneal transmitters for telemetric measurement of body temperature (Tb) and activity. Food deprivation at + 24 degrees C for four days induced a well-defined nocturnal hypothermic response. The normal day-night difference (about 1 degrees C) in Tb increased 1 degrees C per day, reaching 5 degrees C on the fourth night of fast. Nocturnal motor activity decreased during the fast, while daytime activity first increased and then returned to the original level by the end of the fasting period. A strong correlation between Tb and motor activity was found during scotophase (r = .91) but not during photophase (r = .02). At + 4 degrees C, where food was deprived for two days, the level of hypothermia was not different from that at + 24 degrees C, but birds fasting in the cold reached the hypothermic level more rapidly. In control birds, the decrease in Tb at the beginning of scotophase was independent of ambient temperature. In the combined data, the level of hypothermia correlated strongly with body mass loss (r = .90), which shows that quail can directly or indirectly sense the amount of body energy reserves. This is the first report of hypothermia in a fasting gallinaceous bird. The consistent level of hypothermia at varying ambient temperatures suggests that either nonenergetic costs or phylogenetic constraints prevent deeper hypothermia in cold. Accordingly, the regulation of hypothermia cannot be explained by using only energetic arguments.