Double-Brooding in Red-Necked Grebes

-Four attempts of double-brooding (rearing two broods in one year) in the Red-necked Grebe (Podiceps grisegena) in SE Poland were recorded out of 163 breeding pairs studied over the period 1993-1999. Two pairs successfully reared two broods during the same nesting season. Time appears to be an important constraint on the incidence of double-brooding. The pairs attempting double-brooding were among the earliest breeders and the second clutches were started early, relative to the hatching time of the previous brood. All pairs attempting a second brood nested on fry ponds with high fish availability. Double-brooded pairs fed the first-brood young more frequently before the onset and after termination of incubation of the second clutch than did single-brooded pairs during the corresponding period of brood rearing. However, in comparison with single-breeders, parents attempting double-broods were aggressive to the first-brood young earlier and fed them less frequently during the incubation of the subsequent clutch. Apparently only early breeding on territories with abundant food allows grebe parents to overcome conflicting pressures resulting from overlapping parental investment in successive reproductive attempts. Received 8 March 2000, accepted 5 October 2000.