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Seabirds are one of the most threatened of all bird groups, with a marked community-wide decline across the last decades. Yet, some seabird species are more resilient than others, and it is essential to study under which conditions even these highly resilient organisms are affected by global changes. Here, we report such a case in northern gannets (Morus bassanus). Using global location sensors (GLS), demographic and stable isotope analyses, we performed a long-term study of the migration biology and inter-annual survival of gannets breeding on Rouzic Island in Brittany, France. Across 2006–2015, our analyses showed that the birds spent the inter-breeding period off Western Europe, in the Mediterranean or off West Africa. There were no inter-annual trends in the use of these different areas, but isotopic analyses suggested food competition between gannets and industrial-scale fisheries. Crucially, we found a precipitous decline in the return rates of birds equipped with GLS, from 100% in 2006–2007 to less than 30% after 2015. This decline was consistent with a marked decrease in inter-annual survival probabilities for ringed adult gannets, from > 90% in 2014–2015 to < 60% in 2018–2019, and with a population decline of the Rouzic gannet breeding colony in recent years. Strong ecological signals provided by northern gannets point to critical marine ecosystem perturbation in the Eastern Atlantic, and the decline of this resilient and emblematic species should lead to the urgently needed transformation of marine policies. [ABSTRACT FROM AUTHOR]

Identifying the drivers of population fluctuations in spatially distinct populations remains a significant challenge for ecologists. Whereas regional climatic factors may generate population synchrony (i.e. the Moran effect), local factors including the level of density dependence may reduce the level of synchrony. Although divergences in the scaling of population synchrony and spatial environmental variation have been observed, the regulatory factors that underlie such mismatches are poorly understood.Few previous studies have investigated how density‐dependent processes and population‐specific responses to weather variation influence spatial synchrony at both local and regional scales. We addressed this issue in a pond‐breeding amphibian, the great crested newt Triturus cristatus. We used capture–recapture data collected through long‐term surveys in five T. cristatus populations in Western Europe.In all populations—and subpopulations within metapopulations—population size, annual survival and recruitment fluctuated over time. Likewise, there was considerable variation in these demographic rates between populations and within metapopulations. These fluctuations and variations appear to be context‐dependent and more related to site‐specific characteristics than local or regional climatic drivers. We found a low level of demographic synchrony at both local and regional levels. Weather has weak and spatially variable effects on survival, recruitment and population growth rate. In contrast, density dependence was a common phenomenon (at least for population growth) in almost all populations and subpopulations.Our findings support the idea that the Moran effect is low in species where the population dynamics more closely depends on local factors (e.g. population density and habitat characteristics) than on large‐scale environmental fluctuation (e.g. regional climatic variation). Such responses may have far‐reaching consequences for the long‐term viability of spatially structured populations and their ability to respond to large‐scale climatic anomalies. [ABSTRACT FROM AUTHOR]