Brood Desertion in Ducks: The Ecological Significance of Parental Care for Offspring Survival.

The debate concerning the relative importance of the costs and benefits of parental investment decisions has created considerable controversy. This is especially true in the discussion for duck species, where the link between ending of parental care and offspring survival has not been fully determined. This experimental study tests whether mallard ducklings (Anas platyrhynchos; a non-creching species with maternal care-) achieve maximum survival potential before the typical ending of the hen-brood bond. As mortality rates are at their highest during the first two weeks post-hatching, our experimental investigation of survival was restricted to ducklings from 2 weeks of age until fledging, in non-deserted (ND, control group; n=36) and prematurely abandoned (D, deserted treatment group; n=35) broods under free-ranging conditions. The experiment was conducted over two years to take differences in weather conditions into account. According to age periods, survival rates ranged from 65 to 95% in the D group and from 97 to 100% in the ND. Survival probability of deserted ducklings was 23% lower than that of the control group (p 0.09) thereafter. Assuming that the hen-brood bond is time-disrupted at ~6 weeks post-hatching, our results are consistent with the idea that trade-offs associated with the provision and the consequent ceasing of maternal care have evolved according to the intrinsic ability of ducklings to survive on their own at ~4 weeks post-hatching. The dissipation of the behavioural-hormonal processes underlying the hen-brood bond probably requires a delay between these two events. The maintaining of maternal care for ~4 weeks post-hatching also coincides with the most critical periods of duckling vulnerability after hatching, during which the hen has an important anti-predator role to play.