While people have looked for, and found, patterns of synchrony in abundance (count) data, demographic data have been overlooked. Bird ringers throughout Europe collect information on productivity and survival through the Constant Effort Sites Scheme, that is ringing in the same sites with the same effort each year. 

This paper uses data 995 sites, from 12 countries, to examine patterns of synchrony in each of these two rates. Across the 26 species examined, synchrony in productivity operated over larger spatial scales and was stronger, on average, than synchrony in adult survival rates. However, counter to this, synchrony in the count data was consistently lower than for either productivity and survival, suggesting that productivity and abundance synchrony seem to interact to weaken synchrony in abundance.

The relatively strong synchrony in productivity suggests that, during the breeding season, key environmental conditions are correlated over a large proportion of species’ European ranges, for example because of consistent weather conditions occurring over large areas, or more local factors (e.g. agricultural practices) operating in a regionally consistent way. The paper also found that synchrony in populations of resident and migratory species was structured differently indicating they were sensitive to different environmental factors. Understanding the key processes underlying these patterns will be a key next step.

Synchronous fluctuations in species' abundance are influenced by synchrony in underlying rates of productivity and survival. However, it remains unclear how rate synchrony varies in space and time, contributes to abundance synchrony, and differs among species. Using long-term annual count (number of adults captured), adult survival and productivity (number of juveniles captured per adult) data for breeding land-birds at ringing sites across Europe, we show that synchrony is strongest and largest scale in productivity and weakest and smallest scale in counts. However, counts fluctuate more synchronously with survival than they do with productivity. These patterns hold for species which do not migrate or only migrate within Europe (European residents) and those migrating to sub-Saharan Africa (sub-Saharan migrants), but the periodicity of productivity and survival synchrony is longer in European residents than in sub-Saharan migrants. This suggests that survival and productivity synchrony may interact to weaken abundance fluctuations but are influenced by environmental drivers operating over differing timescales in European-resident and sub-Saharan-migrant species.