Costs of reproduction in the Zebra Finch Taeniopygia guttata: Manipulation of brood size in the laboratory

Brood size of Zebra Finches Taeniopygia guttata was manipulated in an attempt to identify a trade-off between current and subsequent reproduction in a laboratory situation with ad libitum food availability. The birds were able to raise a larger brood than the most frequent brood size under the same conditions. Initiation of the subsequent clutch was advanced after raising a small brood, and delayed after raising a large brood. The size of the subsequent clutch was not affected by the previous, experimental brood size. Thus, a cost of reproduction was observed in modification of the reproductive interval. Brood size also affected the prospects of the current, experimental brood. Both nestling survival and nestling weight at independence decreased with brood size. It has often been suggested that food availability limits reproduction in the field. This study shows that under unrestricted access to food, other factors restrain reproduction. Time allocation, energy expenditure and nutrient reserves of the parents are discussed as potential alternative constraints.