Variation in Reproductive Effort in Female Zebra Finches (Taeniopygia guttata) in Relation to Nutrient-Specific Dietary Supplements during Egg Laying

Abstract

Although dietary intake is thought to be more important than endogenous reserves for egg production in small, altricial birds (such as passerines), few experimental data are available to address this question. I investigated the reproductive responses of female zebra finches, Taeniopygia guttata, to enhanced dietary intake of macronutrients during the period of egg formation. Lipid supplementation had no effect on egg or clutch size. In contrast, proteino-supplemented females laid larger 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 cessation of protein feeding). Interindividual egg size variation was maintained on the enhanced protein diet. The effect ofprotein on clutch size was equivocal, with some evidence for a longer-term increase in size of second (replacement) clutches 10-14 d after protein feeding. Increased egg size involved an increase in both yolk protein and albumen content but not yolk lipid content. These data suggest that zebra finches are protein limited during egg production. Body 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, endogenous protein for egg production. However, mass loss was reduced or nonsignificant during laying of second (replacement) clutches with the same number and size of eggs. Mass loss during egg laying may thus have an alternate, more complex, and individually variable physiological basis rather than simply reflect a negative energy or nutrient balance.