Effect of ephemeral food restriction on growth of house sparrows

We tested for the presence of compensatory growth (i.e. faster age-specific growth) following ephemeral periods of food restriction in altricial nestl ings using the House Sparrow (Passer domesticus) as a model species. To sim ulate periods of poor food conditions, we raised nestlings in captivity, fe d them a synthetic diet, and held them at constant body mass for 48 h begin ning on either day 3 or 6 of life. Controls were fed according to an age-sp ecific feeding schedule that yielded normal growth curves. During realiment ation, restricted nestlings did not achieve a faster rate of growth than th at of controls. Instead, these nestlings either died tall controls lived) o r grained mass at a rate similar to that of controls. Consequently, restric ted nestlings reached asymptotic mass two days later than control nestlings . Growth of culmen and tarsus was not affected, but growth of the eighth pr imary was reduced for several days in nestlings restricted at day 6 (i.e. l ate restricted), although this difference disappeared by the age of fledgin g. Because surviving nestlings achieved only a 15.9% increase in food consu mption compared with unrestricted controls and were unable to translate it into a faster rate of growth, the nestlings may have been growing at a maxi mum rate. We found no differences between late-restricted and unrestricted nestlings in % water, % protein, % lipid, and % ash. The two groups were of similar maturity as measured by % body water and the water index. Our resu lts are consistent with current theory in that periods of food restriction delayed the schedule of mass accretion by the length of the restriction per iod. Although House Sparrows have a labile growth rate and developmental ti me, our results did not support the hypothesis of compensatory growth. Base d on this and one other study compensatory growth does not appear to occur in altricial birds.