Reproductive compensation for offspring viability deficits by female mallards, Anas platyrhynchos

The compensation hypothesis (CH) says that when impediments to the expression of mate preferences occur so that reproduction is with nonpreferred (NP) partners, mothers with NP mates compensate for lower-viability offspring through enhanced investment. Previously, we tested an assumption of the CH and showed that offspring viability was significantly lower when mothers reproduced with NP mates. Here we report tests of the CH. Egg mass differed significantly by mother agemate category. Second-year mothers in NP pairings laid significantly heavier eggs than second-year mothers in preferred (P) pairings; mean egg mass of first-year mothers with NP or P mates did not differ. However, mean egg mass per mother and mean number of eggs per mother were positively and significantly related. Thus, there was no trade-off between egg size and egg number for any category of mother. By fledging age, duckling performance, quality and condition were significantly lower for first-year mothers with NP mates compared with those for mothers in the other categories. Second-year, but not first-year mothers, successfully compensated for predictable deficits in offspring viability from reproduction with NP males. This is the first study showing that mothers compensate for viability deficits in offspring resulting from reproduction with NP partners. 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.