VARIATION IN REPRODUCTIVE EFFORT IN FEMALE ZEBRA FINCHES (TAENIOPYGIA-GUTTATA) IN RELATION TO NUTRIENT-SPECIFIC DIETARY-SUPPLEMENTS DURING EGG-LAYING

Although dietary intake is thought to be more important than endogenou s reserves for egg production in small, altricial birds (such as passe rines), few experimental data are available to address this question. I investigated the reproductive responses of female zebra finches, Tae niopygia guttata, to enhanced dietary intake of macronutrients during the Period of egg formation. Lipid supplementation had no effect on eg g or clutch size. In contrast, protein-supplemented females laid large r eggs (10%-12%) than controls, both immediately (i.e., first clutch) and in the longer term (second and third clutches up to 21 d after ces sation of protein feeding). Interindividual egg size variation was mai ntained on the enhanced protein diet. The effect of protein on clutch size was equivocal with some evidence for a longer-term increase in si ze of second (replacement) clutches 10-14 d after protein feeding. Inc reased egg size involved an increase in both yolk protein and albumen content but not yolk lipid content These data suggest that zebra finch es are protein limited during egg production. By mass decreased 2.4 g (15% of initial mass) during the laying cycle in control and lipid-fed females but did not change significantly in protein-fed birds. These mass changes are consistent with the idea that females use stored endo genous protein for egg production. However, mass loss was reduced or n onsignificant during laying of second (replacement) clutches with the same number and size of eggs. Mass loss during egg laying mag, thus ha ve an alternate, more complex, and individually variable physiological basis rather than simply reflect a negative energy or nutrient balanc e.