SCALING NESTLING ENERGY-REQUIREMENTS

The total energy metabolized (TME) by nestling birds. from hatching to fledging, scales as M1.06, with body-mass at fledging (M) explaining 97% of the variation in TME. After statistically removing the effects of body-mass, multiple-regression analysis reveals that 69% of the variation in TME is explained by nestling developmental rate, expressed as the time to fledging (t(fl), days). Together t(fl) and M explain 99% of the variation in TME for the 30 species considered (M range 9.7 to 3700 g). Peak daily metabolized energy (DME, kj/day), the maximum rate at which parents must provision their nestlings, scales with fledging mass as M0.78. Body-mass explains 96% of the variation in nestling peak DME, with 37% Of the residual variation being attributable to the time taken to fledge (t(fl)). Together, t(fl) and M explain 97% of the variation in peak DME. An examination of residuals indicates that adaptive modifications in nestling energetics are attained principally through changes in growth rate, which affect TME and peak DME oppositely. Doubling nestling growth rate increases peak DME by 61%, but decreases total nestling energy demand (TME) by 77%. This opposing effect complicates evolutionary interpretations of avian reproductive patterns.