Assessing the response of mountain birds to rapid environmental change: conservation ecology of the Alpine Ring Ouzel (Turdus torquatus alpestris) - PhDData

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Assessing the response of mountain birds to rapid environmental change: conservation ecology of the Alpine Ring Ouzel (Turdus torquatus alpestris)

The thesis was published by Barras, Arnaud Gian, in September 2022, University of Bern.


Mountain ecosystems are exposed to increasing threats globally, of which changes in land-use and climate are commonly regarded as the most serious. In this context of rapid environmental change, it is of fundamental importance to assess the current and future responses of high-elevation organisms. There is in fact an urgent need to understand the ecological and demographic mechanisms underlying mountain species’ distributions and population trends for proper conservation planning. Here, we focused on the Ring Ouzel Turdus torquatus, an emblematic thrush species of upland and mountainous regions of Europe. The main goal of this PhD thesis was to improve our knowledge of the ecology and demography of the alpestris subspecies, i.e. the Alpine Ring Ouzel, to identify possible drivers of negative trends in central Europe and envision possible conservation action. We first looked at functional ecological relationships, such as patterns of habitat selection and resource acquisition during the breeding season in the Swiss Alps, and how these relate to environmental variables. In a next step, we focused on demographic aspects and described the structure and dynamics of two focal populations in the western European Alps. We then examined behavioural and movement patterns across the annual cycle using tracking devices. Lastly, we relied on the initially accrued knowledge of species’ ecological requirements to parameterize a country-wide, fine-scale habitat suitability model. The latter was used to delineate key areas for the Ring Ouzel and evaluate its vulnerability to environmental change based on various scenarios.

Our results demonstrate specific foraging preferences for soft and moist soils within a short and sparse grass sward, conditions that rapidly vanish from the breeding grounds as the season advances. This underlines strong temporal constraints on breeding, most probably driven by the brief time window of availability of the main prey, earthworms, as corroborated by the observed reduction in provisioning activity and efficiency in dry and warm weather contexts. Variations in weather conditions had, however, no clear impact on fitness parameters. Still, the narrow time window available for reproduction in the Alps may explain the apparent slower life-history strategy of Alpine populations when compared to Northern populations. Retrieved tracking data evidenced flexible seasonal and day-to-day movements but a year-round reliance on high-elevation regions, with winter quarters located in mountain ranges of Spain and Morocco. Finally, we reveal the more prominent role of climate compared to land-use in predictive models of species distribution and abundance. Indeed, climate shifts are expected to override the potential impact of land-use change in the coming decades, such as land abandonment and farming intensification. This highlights the vulnerability of the species to climate disruption, despite the strategies evolved to cope with environmental changes, in particular weather variation. Altogether, our findings unfortunately suggest limited leeway for implementing adaptive conservation strategies capable of fully mitigating the impacts of environmental change on Alpine Ring Ouzels. Nonetheless, recommendations for habitat management are framed while our predictive models constructed on fine-grained ecological information enable spatial prioritization of conservation programmes. These recommendations will not only help to conserve Alpine Ring Ouzels but also to maintain a rich biodiversity in Alpine treeline ecotones into the future.

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