The migration strategy, diet and foraging ecology of a small seabird in a changing environment

This thesis examines the migration strategy, diet and foraging ecology of the smallest Atlantic seabird, the European Storm Petrel Hydrobates pelagicus.Evidence was found for sex-specific migration behaviour, opportunistic feeding, temporal variation in diet, and the strategy regulation of energy reserves in response to varying environmental conditions, as a buffer against starvation during migration. Molecular sexing from feather and faecal samples revealed an unexpectedly strong female bias in the sex ratio of Storm Petrels attracted to tape-lures of conspecific calls, during their northwards migration past the coast of SW Portugal. The thesis describes the development and application of molecular techniques, in combination with stable isotope analysis, to study Storm Petrel diet by the detection of prey DNA from faecal samples. The major category of prey detected was fish (chiefly European Sardines Sardina pilchardus). Other components of the diet were other pelagic and demersal fish species, Cephalopoda (primarily cuttlefish Sepia spp.), Amphipoda, Isopoda and a range of terrestrial invertebrates. Large between-year fluctuations in the level of body reserves carried by these birds were observed over the 21-year study period (1990-2010). The pattern of body mass variation followed a smooth oscillation, which was not an artefact of differences among years in the distribution of capture effort, body size or sex ratio changes. Local sea surface temperature (SST), net primary production (NPP) and European Sardine biomass were key factors associated with between-year changes in Storm Petrol body reserves. These associations suggest that Storm Petrels strategically regulate their body reserves to buffer against starvation in years of low food abundance