Intraspecific variation in egg size, clutch size, and timing of laying was studied in captive-breeding zebra finches (Taeniopygia guttata) maintained under conditions of constant temperature, humidity, photoperiod (14 h light: 10 h dark), and ad libitum food supply. Individual variation was marked in the experimental population: egg size 0.915–1.342 g, clutch size 2–7 eggs, and laying interval 4–13 days; however, within individual females egg size (r = 0.742) and clutch size (r = 0.588) were highly repeatable between first and second clutches. Body condition explained only 8% of egg size variation, and clutch size and laying interval were independent of body condition. Clutch size was negatively related to laying interval: females laying later relative to pairing laid smaller clutches (b = −0.175 eggs/day). Body mass of breeding females decreased by 1.57 g (9% of initial mass) during laying of first clutches; mass loss was positively related to initial body condition (R2 = 27.8%) and total clutch mass (R2 = 7.6%). Mass loss was lower (0.47 g) during laying of second or replacement clutches than during laying of first clutches. Individual variation in reproductive effort in captive-breeding zebra finches is very similar to that in free-living avian populations. Laboratory studies on captive-breeding species can provide a valuable approach for the study of proximate physiological mechanisms underlying intraspecific variation in reproduction.
Colocalization of Immediate Early Genes in Catecholamine Cells after Song Exposure in Female Zebra Finches (Taeniopygia guttata)