Intra- and inter-individual variation in reproductive effort in captive-breeding zebra finches (Taeniopygia guttata)

Abstract

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.