Long-term changes in climate are affecting the abundance, distribution and phenology of species across all trophic levels. Short-term climate variability is also having a profound impact on species and trophic interactions. Crucially, species will experience long-and short-term variation simultaneously, and both are predicted to change, yet studies tend to focus on only one of these temporal scales. Apex predators are sensitive to long-term climate-driven changes in prey populations and short-term effects of weather on prey availability, both of which could result in changes of diet. We investigated temporal trends and effects of long-and short-term environmental variability on chick diet composition in a North Sea population of European shags Phalacrocorax aristotelis between 1985 and 2014. The proportion of their principal prey, lesser sandeel Ammodytes marinus, declined from 0.99 (1985) to 0.51 (2014), and estimated sandeel size declined from 104.5 to 92.0 mm. Concurrently, diet diversification increased from 1.32 (1985) to 11.05 (2014) prey types yr −1 , including members of the families Pholidae, Callionymidae and Gadidae. The relative proportion of adult to juvenile sandeel was greater following low sea surface temperatures (SSTs) in the previous year. In contrast, the proportion of Pholidae and prey richness were higher following high SST in the previous year. Within a season, the proportion of sandeel in the diet was lower on days with higher wind speeds. Crucially, our results showed that diet diversification was linked to trends in SST. Thus, predicted changes in climate means and variability may have important implications for diet composition of European shags in the future, with potential consequences for population dynamics.

Populations of marine top predators are exhibiting pronounced demographic changes due to alterations in prey availability and quality. Changes in diet composition is a key potential mechanism whereby alterations in prey availability can affect predator demography. Studies of long-term trends in diet have focused on the breeding season. However, long-term changes in non-breeding season diet is an important knowledge gap, since this is generally the most critical period of the year for the demography of marine top predators. In this study, we analysed 495,239 otoliths from 5888 regurgitated pellets collected throughout the annual cycle over three decades (1985-2014) from European shags Phalacrocorax aristotelis on the Isle of May, Scotland (56°11′N, 02°33′W). We identified dramatic reductions in the frequency of lesser sandeel Ammodytes marinus occurrence over the study, which was more pronounced during the non-breeding period (96% in 1988 to 45% in 2014), than the breeding period (91-67%). The relative numerical abundance of sandeel per pellet also reduced markedly (100-13% of all otoliths), with similar trends apparent during breeding and non-breeding periods. In contrast, the frequencies of Gadidae, Cottidae, Pleuronectidae and Gobiidae all increased, resulting in a doubling in annual prey richness from 6 prey types per year in 1988 to 12 in 2014. Our study demonstrates that the declining importance of the previously most prominent prey and marked increase in diet diversity is apparent throughout the annual cycle, suggesting that substantial temporal changes in prey populations have occurred, which may have important implications for seabird population dynamics.

With 5 figures in the text)During the recovery of the population of dark-bellied brent geese Branru herniclu bernicla, traditional wintering sites in Britain have experienced increases in numbers and new sites have been colonized. Goose counts were used to describe the migration phenology and winter use of Scolt Head, north Norfolk (a traditional site) and the Burry Inlet, South Wales (a relatively new site) over the period of re-colonization and colonization, respectively. During the 1950s, only a few hundred birds wintered at Scolt Head, and most stayed for only a short period. By the late 1980s/early 199Os, numbers had reached several thousands, their period of stay was longer and there was little variation between years in median arrival (28 October) and departure (1 1 March) dates. A similar process was observed during the entire colonization phase at the Burry Inlet; initially birds arrived late and departed early, but arrived progressively earlier and departed later as wintering numbers increased. The autumn arrival rates at both sites were slower than the spring departure rates. During years of good breeding productivity, those adults with young arrived slightly later in Norfolk than failed breeders and non-breeders, and a higher proportion of young birds remained in spring after the main departure. However, the overall pattern of arrival and departure did not vary according to whether there had been a good or poor breeding season. Some adults of breeding age also remained until May. The effects of food depletion and use of novel feeding habitats in relation to migration phenology and winter use of sites are discussed.

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