GROWTH, THE DEVELOPMENT OF ENDOTHERMY, AND TORPIDITY IN BLUE-NAPED MOUSEBIRDS UROCOLIUS-MACROURUS

Blue-naped Mousebirds are altricial birds that are naked and blind at hatching. The nestling period is extremely short (12.5+/-0.8 d). Durin g the first 7 days the nestlings are unable to thermoregulate actively but from 3 day old the nestlings already show approximately the same body temperature (T-b) as adults under ''natural conditions'' in the n est with siblings. At an ambient temperature (T-a) of + 35 degrees C t he nestlings are nearly endothermic by the age of 9 days (T-b 39.1+/-0 .8 degrees C) and within 12 days individual birds are essentially endo thermic at T-a + 20 degrees C (T-b 39.4+/-0.4 degrees C = 97% of adult -T-b). At this age the birds leave the nest. They are sufficiently fea thered but still unable to fly and have only reached 55% of adult mass . Coordinated shivering thermogenesis was observed for the first time on day 6 (T-a + 20 degrees C), and panting and gular fluttering for co oling from day 4. Torpor, as a special energy saving mechanism, was sh own first at an age of about 10 days (T-a + 15 degrees C).