Hatching Asynchrony Reduces Parental Investment in the Jackdaw

(1) Twenty-two control pairs of jackdaws, Corvus monedula, hatched their clutches asynchronously over a mean of 2.7 days. Hatching synchrony was induced experimentally in sixteen further broods by transferring chicks hatched on the same day from two or three nests into a single nest. The transfer had no effect on chick survival. (2) The within-brood variation in weight (the `brood hierarchy') was greatly reduced in experimental broods relative to control broods. (3) In both control and experimental broods more than 80% of chick mortality was through starvation, and only 5% through predation. (4) In both control and experimental broods, chicks high in the brood weight hierarchy had a greater fledging success than those low in the hierarchy, and chicks starved sequentially in reverse order of their position in the hierarchy (lightest first, etc.). The effect of position in the hierarchy on fledging probability did not differ for control and experimental chicks. (5) Control and experimental broods did not differ in the number of chicks fledged. Control and experimental chicks did not differ in weight, wing length or tarsus length at 26 days of age. (6) Parents that reared control (asynchronous) broods wasted less parental investment than parents that reared experimental (synchronous) broods, because control chicks that starved did so at a younger age than experimental chicks.