DZIALOWSKI, E; BURGGREN, W; TAZAWA, H; Univ of North Texas, Denton; Univ of North Texas, Denton; Muroran Institute of Technology, Muroran, Japan: Development of Endothermy in Emu (Dromaius novaehollandiae) Embryos and Hatchlings

Endothermy develops after external pipping in most precocial bird species. In this study we examined the development of endothermy in the embryos and hatchlings of a large bird, the emu. We measured metabolic rate (VO₂) and surface temperature responses to changes in air temperatures from 22&deg C to 35&deg C. Prior to internal pipping on day 48 of incubation, embryos maintained a constant VO₂ during both warming (135 ml O₂ / hr) and cooling (128 ml O₂ / hr) periods. A similar response was observed for internally pipped embryos on day 49 of incubation. Prior to external pipping, the VO₂ of embryos appeared to be limited by the oxygen conductance of the eggshell. Upon externally pipping on day 50, the emu embryos exhibited the ability to significantly increase VO₂ in response to cooling, from 239 to 567 ml O₂ / hr (p<0.05). Emu hatchlings as early as day 0 have the ability to regulate body temperature by altering VO₂ under the conditions tested. Upon cooling, the VO₂ of day 0 hatchlings increased significantly from 203 to 581 ml O₂ / hr (p<0.05). Day 1 to 3 emu hatchlings showed a similar change in VO₂ during cooling. As hatchlings, differences in skin temperature during cooling and warming diminished as the animals aged. On day 0, the difference between warming and cooling skin temperature was 5&deg C, but by day 3 the difference decreased to only 1.6&deg C. Emu embryos develop the ability to increase VO₂for thermoregulatory purposes prior to hatching, but they are oxygen conductance limited. Hatchling emu have the ability to maintain homeothermy through the increase of VO₂.