Population and demographic synchrony in European land birds.

Understanding the drivers of spatially and temporally correlated (synchronous) fluctuations in abundance is a fundamental challenge in ecology and conservation. Synchronous fluctuations in different demographic rates can potentially drive or dampen abundance synchrony, but demographic synchrony is generally poorly understood. Using long-term count and demographic data for breeding land-birds at sites across Europe, we show that the strength and scale of synchrony are greatest in productivity, followed by adult survival rates and then counts. However, count fluctuations are more synchronous with survival than with productivity. Despite migratory and resident species having similar periodicities of count synchrony, synchrony in both demographic rates was more common over long-timescales in resident species and short-timescales in migrant species. These findings suggest local impacts of synchronous fluctuations in adult survival rates on count synchrony, potentially dampening effects of large-scale synchrony in productivity, and that the environmental drivers of synchrony may differ between residents and migrants.