Population ecology and management of waders breeding on coastal meadows
Sammanfattning: Many wader (Charadrii) populations are declining throughout in Europe, but the underlying causes are often poorly known and diverse. To fully grasp the reasons behind declines in vulnerable wader populations, it is crucial to understand the demography. In my thesis, I have focused on the viability and management of waders occurring on coastal meadows in the Baltic Sea using redshank (Tringa totanus) as a model species. I have collected data on demographic parameters in a redshank population on Gotland. I also collected DNA samples of redshanks from several populations in northern Europe to investigate population genetic structure. By using two genetic methods, sequencing mitochondrial DNA and screening AFLP (Amplified fragment length polymorphisms), I found some evidence in the redshank of a recent expansion from a bottle-necked population. I also found significant genetic differentiation between suggested subspecies in Europe but not between populations within the Baltic region. This indicates that redshank populations in Europe constitute at least three separate management units. Survival of redshank nests was low in my study area due to predation, mainly by corvids and foxes. Nest success was not related to habitat characteristics at a local scale. I found no significant effects on nest success of distances to habitat edge or to nearest potential lookout for avian predators. Abundance of an aggressive species with active nest-defence did not have any significant effects on nest survival rates, nor did vegetation concealment. Furthermore, nest success differed between years and was lower later in the season. On average, only 19% of nests survived until hatching, and only 13% of chicks survived until fledging. Adult survival of redshanks on Gotland was slightly higher (80%) than previous estimates (72-77%). By using deterministic population matrix modelling, I found evidence of non-viability in the redshank population on Gotland suggesting that management actions might have to be taken to prevent population decline. The results of the modelling indicate that it is important to preserve the already high adult survival but also to improve survival of nests and chicks simultaneously. Finally, I evaluated population trends over time of four wader species on the Baltic island of Öland and tested for spatial heterogeneity in population trends. Breeding densities of investigated species were positively related to grazing management and local changes in management affected the local change in wader densities. However, average grazing intensity increased over time whereas wader numbers generally remained constant or declined; thus, changes in grazing intensity could not explain changes in overall breeding numbers.
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