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).