Conspecific brood parasitism (CBP) is a taxonomically widespread reproductive tactic. One of the earliest hypotheses put forward to explain the evolution of CBP was "risk spreading"; that is, by laying eggs in more than one nest, parasites may increase the likelihood that at least one offspring will survive to independence. However, the risk spreading hypothesis, based on the assumptions of random nest predation and random selection of target nests by parasites, was theoretically refuted soon after its appearance. New results from the common goldeneye (Bucephala clangula) have revealed that nests are not predated at random and that parasites preferentially lay in safe nests. By taking into account these findings and by modifying accordingly the basic assumptions of the earlier model that refuted the risk spreading hypothesis, we built a model to address the role of nest predation in the evolution of CBP. Model simulations revealed that the selective advantage of parasitic laying, related to nest predation, is much higher than previously thought. Furthermore, the invasion probability of parasitic tactic when initially rare was reasonably high within our model framework. We show that the use of risk assessing, instead of random risk spreading, makes parasitic laying evolutionarily advantageous.

We investigated whether the degree of exchange with other populations affects the occurrence of density‐dependent regulation. We contrasted data from an Icelandic and a Finnish population of breeding wigeons (Anas penelope), the former population being more closed than the later. We looked for density dependence in time‐series data and investigated whether breeding success is density dependent and plays a role in population dynamics and regulation. Time‐series analysis did not reveal density‐dependent regulation in either population. Nor did we find evidence of density‐dependent breeding success in either population. However, population growth rate appeared to be strongly dependent on the breeding success in the previous year in the closed population but not in the open population. Our findings underline how important it is to link time‐series analysis to the study of potential stabilizing mechanisms in order to understand population dynamics and regulation. We also suggest that it may be a difficult task to achieve sustainability in waterfowl harvesting, the theoretical basis of which is density‐dependent population regulation.

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