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 reprodu ction 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 wa s advanced after raising a small brood, and delayed after raising a la rge brood. The size of the subsequent clutch was not affected by the p revious, experimental brood size. Thus, a cost of reproduction was obs erved in modification of the reproductive interval. Brood size also af fected the prospects of the current, experimental brood. Both nestling survival and nestling weight at independence decreased with brood siz e. It has often been suggested that food availability limits reproduct ion in the field. This study shows that under unrestricted access to f ood, other factors restrain reproduction. Time allocation, energy expe nditure and nutrient reserves of the parents are discussed as potentia l alternative constraints.