Impacts of climate change on woodland birds; From individual behaviour to population change

Long-term demographic studies are vital for understanding trends in population size, such as the rapid decline of many bird species. Studies of trophic cascades provide a mechanistic understanding of how populations respond to climate change. The mis-match between timing of food availability and food requirements of nestlings is implicated in the rapid declines of woodland-breeding bird populations. I report the decline of the Pied Flycatcher, Ficedula hypoleuca, and investigate and model its demographic changes. I used a long-term citizen-science dataset of Pied Flycatcher population characteristics (collected 1990-2016 in south Wales), and conducted studies linking weather conditions, invertebrate availability and breeding biology (2016-2018). I used these data to investigate the consequences of laying date on adult annual survival and recruitment, and examined the consequences of changes in the timing of breeding in consecutive years and generations. The study population has declined by 66%. Temperature and rainfall had interacting and non-linear impacts on the breeding cycle. Fledging success was a significant predictor of the next year’s population size. Warmer and more variable conditions were associated with earlier invertebrate phenology and variation in availability, with a phenological mis-match between peak chick food demand and caterpillar availability. Most Pied Flycatcher nesting attempts were timed to allow for successful fledging, but later nests tended to be less successful. Early-laying birds a had higher fledging success and a higher probability of surviving. A stochastic Integral Projection Model predicts that the ongoing decline in the population will continue, leading to extinction within the next 5-15 years. A greater consistency in laying dates of early laying individuals leads to higher annual adult survival. Between-year consistency in laying date had the greatest impact on population growth, and appears to be the strongest mechanism by which this population could avoid extinction