Later onset of breeding in an apex predator in response to climate change: causes and consequences

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Climate change poses one of the most fundamental risks to wildlife populations and biodiversity in the 21st century. Long-term studies are vital to obtain a deeper understanding of the causes and consequences of this change, especially in apex predators. In a population of common buzzards Buteo buteo, average onset of breeding has shifted backwards by over a week over the time period 1990-2010, despite warmer temperatures. We propose to explore which mechanism might best explain this paradoxical result and elucidate the complexity of organisms’ responses to climate change. With data covering breeding times, reproductive success, life histories of individuals and fitness, six major hypotheses can be tested. Is later breeding explained by an adaptive evolutionary response, phenotypic plasticity, relaxed selection pressure by climate, worsening of individual condition, or changes in the age structure or plumage distribution? How does the most likely mechanism interact with the life history to influence population dynamics? Over 500 life histories compiled across 22 years will document shifts in trade-offs between cohorts in response to climate change. Population dynamics will be modelled with time series analyses and matrix models with weather as a covariate to find key factors influencing population growth and fluctuations. Results will be generalized to another apex predator, the goshawk Accipiter gentilis which has been studied in the same study area since 1975. Using two species and the same area, allows general correlates of population growth and fluctuations to be found. Results will be further generalized using a unique continental scale metadata set on common buzzard population dynamics with currently 115 time series of at least 10 year duration.