Short-term changes in incubation temperature: behavioral and physiological effects in the chick embryo from 6 to 20 days.

In 3 experiments we have attempted to determine the extent to which the chick embryo is behaviorally and physiologically responsive to short term changes (.5-2 hr) in the normal ambient incubation temperature. Embryos ranging in age from 6-20 days of incubation have been examined after exposure to temperatures ranging from 30.5 degrees to 44.4 degrees C (normal incubator and nesting temperatures are 37-38 degrees C). At 6,9 and 12 days of age the heart rate and the duration of amnion contractions were significantly altered by exposure to temperature either higher or lower than normal although overt neuromuscular activity (motality) remains unchanged. At 15 and 20 days, however, (hatching occurs on Day 21) the rate of neuromusclar activity is altered at both low and high temperatures. At 20 days, beak-clapping, vocalization, and respiration rates also change reliably upon short-term exposure to both high and low temperatures. The possibility is discussed that embryonic responsiveness to temperature changes in the environment during natural incubation may play some role in later behavioral capabilities.