نبذة مختصرة : International audience ; BACKGROUNDBirds that breed in the northern hemisphere generally migrate to warmer southern regions for the winter. Surprisingly, two populations of diving ducks overwinter mainly in the north of their breeding range. Is this northern strategy the result of a lack of potential habitats in the south or other factors make this strategy more favourable?METHODDesign: Comparison of the actual proportion of birds migrating north with the proportion resulting from simulated distributions of birds under H0: “Ducks distribute themselves to the available wetlands regardless of migration direction; only the presence of potential habitat within a compatible distance matters” Biological data: period 2004-2020: ~ 1,500 banded birds in western France during the breeding season (see map) ; in winter, 20% resighted & 11% recovered Environment data: 3 Copernicus data sets EU-Hydro – Temperature – PrecipitationCONCLUSIONFindings: Migration patterns are not explained by a lack of potential habitat in the south. Birds pursuing a northern strategy to spend the winter seem to be selected or simply favour this strategy.Recent changes in climatic conditions may be the main factors: loss of habitat quality in the south due to drought, gain in habitat quality in the north due to more water recharge, recent gain in habitat quantity in the north due to new ice-free wetlands.The strong disparity in hunting pressure between countries could reinforce selection in favour of birds pursuing a northern strategy outside France.So what now? Even if hunting pressure decreases in the coming years due to the uncertain conservation status of these populations, the northern wintering strategy is likely to be favoured in the coming decades due to the expected changes in climatic conditions.
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