| Summary: | The population size of the horned grebe, Podiceps auritus, is declining in most of the world due to loss of wetlands, deteriorating water quality and establishment of predatory fish such as pike, Esox lucius, in former fish free wetlands. The horned grebe is now globally classified as vulnerable. In this study, data on population dynamics of the horned grebe in six created wetlands in Linköpings kommun was examined together with field work carried out in three of the wetlands. The results indicate that the number of pairs and juveniles of horned grebe crash six to eight years after the wetland is created and does not recover if there is fish present. The pairs and juveniles of horned grebe decreased significantly with the increasing age of the wetland if there was pike present in the wetland. Reduction fishing and drainage of the water in two of the wetlands inhabited pike showed a small improvement in population size of the horned grebe, but the numbers ultimately declined after a few years. Reduction fishing of common roach in one wetland showed a continuing improvement in the population size of horned grebe. Other factors that affected the horned grebe negatively, was an abundance of macrophytes such as Canadian pondweed, Elodea canadensis, that makes foraging harder.
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