The ontogeny of homeothermic regulation in post-hatching chicks: its influence on the development of hearing.

1. The maturation of homeothermy in chicks from day 0 to day 30 after hatching (P0-P30) was studied by measuring rectal temperatures following different environmental exposures. 2. Body temperature regulation and an adult-like temperature (41.5 degrees C) develop with different time courses, being mature on days P4 and P23, respectively. After 1 hr at 20 degrees C, P0 chicks were 4.5-6.5 degrees C cooler than P30 animals. 3. A temperature effect shifts frequency in the auditory pathway up to 0.5 octaves to lower values. Some shifts in tonotopic maps observed in developmental studies of frequency representation in awake chicks can be fully explained by this temperature effect.