Animal migration is a permanent source of wonder. Billions of birds connect regions (and people!) widely separated, redistributing themselves over the planet. Migratory birds also are amongst the most threatened by global change. But our understanding of migration is still limited in multiple aspects, which has implications for our ability to conserve species and to use them as monitors of the global (marine) environment. Very few studies have tracked large numbers of individuals of the same population over multiple seasons, despite the enormous potential for insights and tests of hypotheses related to the causes and consequences of intra-population variation, with implications for the understanding of the evolution of the migratory phenomena. Indeed, our own ongoing combined demographic and long-term migration studies of Cory’s shearwaters (CS) arguably are the most detailed and comprehensive in existence for a single study system (more than 320 migratory tracks already obtained, from 2006 until present; 20 papers on this study system).
The present project will build on our past efforts. CS are particularly suited because of their within-population varied migratory strategies, with multiple wintering areas spanning across the entire Atlantic and into the SW Indian oceans. We have shown that individuals are generally faithful to their wintering areas and migratory routes, but that a sizeable minority can change its destination from one year to the next, often dramatically, switching between hemispheres or across ocean basins. Some variability is explained by sex and by carry-over effects resulting from reproduction. Nevertheless, much variation is still to be explained, and the present project aims to contribute to this, by doing a comprehensive and unprecedented exploration of the factors underlying intra-population variation in migratory behaviour. Behavioural syndromes are attracting much attention in ethology, but virtually no work has been carried out in relation to migration. We will investigate the existence of behavioural syndromes in CS, their heritability, and their relationship to migratory strategies. We will also assess the ontogenetic development of spatial behaviour in CS. We will further develop our study of carry-over effects from breeding into the migratory non-breeding season by, for example, manipulating the health-state of experimental subjects by treating them for gastrointestinal nematode infection. Migratory decisions will potentially have an impact on the birds’ condition and ability for a timely travel back, both factors influencing subsequent fitness components, including breeding performance. Our extensive dataset will enable comparing individuals using different wintering areas in the same season, as well as the effects on the same individual of different choices in different years. The effect of wintering area use will be assessed in parameters such as timing of arrival at the colony, probability of breeding, breeding output, body condition and cellular ageing (telomere shortening). The use of different wintering areas will also expose the birds to different levels of environmental contamination by pollutants. This will be assessed by analyses of concentrations in feathers (for mercury) or in the uropigeal gland secretions (for plastics), allowing the use of one single model organism for environmental monitoring at the scale of an entire ocean basin. Climate change is already altering the migratory behaviour of birds. However, long-term datasets of movements are scarce, and they have been mostly related to changes in temperature. We will relate the migratory choices and performance of CS to current wind conditions and their variability, evaluating also the impacts this has on demography. This will allow predictions in scenarios of future shifts in wind fields related to climate change. Amongst the innovative approaches of our project, highlights include: (1) experimentally improving the health state of study birds to evaluate its impact on migration and winter distribution; (2) relate individual personality and quality to migratory strategy; (3) measure the impact of migratory choices on cellular ageing; (4) simultaneous tracking of parent and recruited offspring (birds of known pedigree) to evaluate the existence of an heritable component in migratory behaviour; (5) predict the impact of changing wind fields on the movements and, ultimately, on demography of a pelagic predator.
This project will contribute to the international body of knowledge on migration strategies by considerably developing what already is a leading single-species long-term study, and will represent a major contribution to national knowledge on the environmental conditions and pollution in the extensive marine area under Portuguese jurisdiction (and beyond). National researchers will improve competence in, inter alia, cellular ageing and monitoring of pollutants in avian tissues.