A. Lill et Pj. Fell, ASPECTS OF THE ECOLOGICAL ENERGETICS OF DEVELOPMENT IN RAINBOW BEE-EATERS, Australian journal of zoology, 45(3), 1997, pp. 281-294
Prefledging developmental energetics of rainbow bee-eaters were invest
igated by comparing the mass, water fraction and energy density of the
egg, hatchling and fledgling, determining the growth rate and pattern
of the nestling and documenting the reproductive time investments of
breeders. The incubation and nestling periods greatly exceeded allomet
ric predictions. On average,the egg contents contained 26% yolk, 80% w
ater and had an energy density of 25.82 kJ g(-1) dry mass. The 3.3-g h
atchling contained 83% water and had an energy density of 21.28 kJ g(-
1) dry mass; its size and composition suggested that it was not except
ionally mature and thus that embryonic growth was inherently slow, but
no extra energy loading was evident in the egg to meet the predicted
high maintenance costs. Nestling growth was also inherently slow, K fo
r the logistic growth model being 0.266 and t(10-90) 16.5 days. Nestli
ngs attained asymptotic mass after about two-thirds of the nestling pe
riod had elapsed, exceeded adult mass by up to 3.5-g and then underwen
t a 15% prefledging mass recession. Fledglings contained 67% water, ha
d a mean energy density of 23.33 kJ g(-1) dry mass and were capable of
efficient flight. Nestling growth was highly labile and intrabrood ma
ss hierarchies and brood reduction through nestling starvation were co
mmon and may be adaptations to short-term food shortages. The mean inc
ubation constancy (54% of daytime) and the mean nestling feeding rate
of 4 meals per nestling h of breeders were comparatively low; the form
er probably reflects the insulation of the burrow from ambient tempera
ture oscillations and the latter the slow nestling growth rat, Members
of breeding pairs often contributed to feeding the brood quite dispar
ately and auxiliaries' contributions in the 24% of breeding units that
contained them were relatively small. The unpredictable nature of the
species' aeroplankton diet may have favoured slow nestling growth thr
ough its influence on breeders' food gathering capacity and by favouri
ng a relatively high degree of physiological maturity and self-suffici
ency in fledglings.