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From individual behaviour to population dynamics in the Oystercatcher using spatially and temporally explicit approaches

Final Activity Report Summary - BIRD SPATIAL ECOLOGY (From individual behaviour to population dynamics in the Oystercatcher using spatially and temporally explicit approaches)

On our planet where human activity is more and more in conflict with the natural environment, it becomes essential to predict the impact of habitat change and habitat loss on biodiversity. Using past events of habitat loss, it is possible to built models to estimate the most likely response of animal population dynamics to habitat change in order to propose mitigation measures beforehand. Migratory birds are interesting models for such questions since their high mobility enables them to move quickly in case of habitat change. However the survival of displaced populations of course depends on the availability of good quality substitution habitat. During this project we worked on the improvement of methods to estimate survival and movements of birds in a context of past habitat change. These improved methods will subsequently serve as a basis for the development of new population dynamic models for predicting the impact of future habitat change. The Oystercatcher Haematopus ostralegus is an important wader species of estuaries of Northern Europe but its population declined by 40% in the Netherlands, one of its wintering strongholds.

We developed a new multistate capture-recapture model to estimate survival and movements between wintering sites using large ringing datasets both at a regional scale, the Dutch Delta, and at a continental scale. For the Dutch Delta, a large ringing dataset was available over a period of 20 years, before and after the completion of a storm surge barrier in 1986 that removed 33% of the tidal flats. For the continental scale, a comparison of movements of resident and migrant wintering populations was made between the Wadden Sea, the Dutch Delta, and the Northern French coast, including the ringing datasets from 10 countries from continental Europe over 25 years. We found that habitat change did induce a decrease in survival, particularly when it coincided with severe winters or food shortage, but not necessarily a redistribution of birds affected by the changes. This means that the specific behaviour of the bird species under study (e.g. a strong fidelity to territory in the Oystercatcher) must be taken into account for predicting the impact of habitat change on the population. Our results emphasise the need to continue such large ringing schemes and to analyse the large amount of ringing data already available in various national ringing centres. It therewith also highlights the need to improve the international coordination and availability of these data, for instance within the framework of the EURING project.

The next step is to predict movements and survival of migratory bird populations in the future. Up to now, only optimal-migration behaviour-based models could be used for such purposes while individual behaviour-based models (IBBM) focused only on the wintering period. Since the Oystercatcher analyses were not finished, we parameterised for the first time an IBBM for the spring migration of Pink-footed geese Anser brachyrhynchus from Denmark to Svalbard, in order to compare its outcome with previous results obtained with an optimal migration model developed at our institute.

We found that for both models the most important factors driving the spring migration for geese is the timing of food availability (newly-grown grass rich in nutrients). Moreover the IBBM could be used to investigate in more detail the mechanisms underlying migratory decisions and we found that the environmental cues used by birds can differ between staging sites (food availability in the South and internal clock when approaching the arctic breeding grounds). These results will be useful to predict population dynamics and habitat use of migratory geese in the coming decades when the timing of food availability will be advanced because of climate change.