Assessing the impact of climate change in an avian apex predator from 1990 to 2025

Science is facing a paradox. On the one hand, climate change has become a major threat for biodiversity and humanity, implying an urgent need for data about its impacts. On the other hand, financing bodies are becoming reluctant to invest in the acquisition of long-term data, although they can help assess the impact of global changes. It therefore appears to be very important to invest in

those biological systems for which data have already been collected for decades and to make sure that the data are correctly implemented in databases. This is necessary particularly when a long-term project will continue even after the person who started this program retires. This type of data is a goldmine to tackle the biological effects of climate change and other human-related biological effects that may become even worse in the future.

Despite numerous studies have demonstrated that climate change affects phenology (timing of migration and reproduction date), the effect on fitness and life-history traits remains largely unstudied. Analyzing long-term datasets is an irreplaceable approach before planning experimental studies to identify the exact mechanisms underlying the detrimental effects of climate change. The impact could be via the rise in temperature, a change in the precipitation regime, or to any other human-induced changes in environmental quality, such as a deterioration in foraging conditions or a rise in pollution (including light pollution for nocturnal species).

In the present project, we intend to take profit of a long-term dataset collected in the barn owl (Tyto alba), a species studying since 1990 in western Switzerland. This species is particularly interesting because it is an apex predator which lives in human-modified habitats. It can therefore be considered as a bioindicator of intensively exploited farmland and be very helpful for the conservation of the other species living therein.

In our study area, barn owl annual population size varies from 10 to 200 breeding pairs. This offered us the possibility to collect a lot of data on a large number of reproductive parameters (laying date, clutch size, egg size, hatching success, nestling growth, fledging success, offspring sex ratio), morphological data (body size, plumage traits) and life history traits (age at maturity, lifetime

reproductive success, survival). We will analyze this body of data in two ways.

First, we will examine how these parameters changed along the years. Possessing data collected for 32 years (to be continued) gives us the necessary statistical power to detect temporal modifications in reproductive, morphological and life history parameters. Given that since 1990 nature experienced major global changes, such as climate, agriculture and pollution, analyzing temporal changes in biological parameters is key to assess the extent to which human activities altered biological systems. In a second step, we will investigate how climate (temperature and precipitation), farming practices and prey abundance account for temporal changes in biological parameters. This will provide a robust approach to test the effects of climate change and other human-modified environmental factors on the biology of an apex predator.

This project is of importance for several reasons. First, it will indicate how climate change (and other related factors) modified the biology of a well-studied predator, the barn owl, living in farmland, an ecosystem that suffered from human activities. Second, based on the obtained results, we will propose relevant hypotheses to be tested experimentally. Third, the support from SNF will help us to

make sure that the >32 years database is perfectly implemented in a repository, which is the prerequisite for studies on the short-term (e.g. studies we are performing on genomics, movement ecology, etc.) and on the long-term.