ENERGY AND NUTRIENT USE DURING MOLT BY WHITE-CROWNED SPARROWS ZONOTRICHIA-LEUCOPHRYS-GAMBELII

The apparent nutrient and energy costs of moult in Gambel's Sparrows estimated from the materials deposited in the integument are relatively mild compared with the maintenance requirements (5.3% of BMR, and 45% of the minimum maintenance requirement for protein (MMRP)) and with those of reproduction (34% BMR and 165% MMRP), except perhaps for cystine. Measures of the actual costs of moult indicate that processes in addition to plumage synthesis combine to create daily energy costs for peak moult equaling 58% BMR. These processes include (1) recrudescence of the integument, (2) a cyclic osteoporosis, and (3) a large diel cycling in body protein content (as much as 8%). The main adjustments in nutritional requirements during moult are greater needs for protein to supply substrate and for energy. Also, the needs for iron for erythrocyte production (item 1 above) and for calcium for bone formation (item 2 above) presumably increase. Analyses of several food groups reveal that the energy and essential amino acid (EAA) needs for moult can likely be met by a wide variety of food types. When the total daily EAA needs of moulting birds are taken together the profile of the EAA demands is realigned so that the disproportionately high demand for cystine for keratin synthesis is obscured. Consequently, dietary protein can be used more efficiently for whole-body protein synthesis.