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Salinization is having a major impact on wetlands and its biota worldwide. Specifically, many migratoryanimals that rely on wetlands are increasingly exposed to elevated salinity on their nonbreedinggrounds. Experimental evidence suggests that physiological challenges associated with increasingsalinity may disrupt self-maintenance processes in these species. Nonetheless, the potential role ofsalinity as a driver of ecological carry-over effects remains unstudied. Here, we investigated the extentto which the use of saline wetlands during winter – inferred from feather stable isotope values – inducesresidual effects that carry over and influence physiological traits relevant to fitness in black-tailedgodwits Limosa limosa limosa on their northward migration. Overwintering males and females weresegregated by wetland salinity in West Africa, with females mostly occupying freshwater wetlands.The use of these wetlands along a gradient of salinities was associated with differences in immuneresponsiveness to phytohaemagglutinin and sized-corrected body mass in godwits staging in southernEurope during northward migration – 3,000 km from the nonbreeding grounds – but in males only.These findings provide a window onto the processes by which wetland salinity can induce carry-overeffects and can help predict how migratory species should respond to future climate-induced increasesin salinity.

Salinization is having a major impact on wetlands and its biota worldwide. Specifically, many migratoryanimals that rely on wetlands are increasingly exposed to elevated salinity on their nonbreedinggrounds. Experimental evidence suggests that physiological challenges associated with increasingsalinity may disrupt self-maintenance processes in these species. Nonetheless, the potential role ofsalinity as a driver of ecological carry-over effects remains unstudied. Here, we investigated the extentto which the use of saline wetlands during winter – inferred from feather stable isotope values – inducesresidual effects that carry over and influence physiological traits relevant to fitness in black-tailedgodwits Limosa limosa limosa on their northward migration. Overwintering males and females weresegregated by wetland salinity in West Africa, with females mostly occupying freshwater wetlands.The use of these wetlands along a gradient of salinities was associated with differences in immuneresponsiveness to phytohaemagglutinin and sized-corrected body mass in godwits staging in southernEurope during northward migration – 3,000 km from the nonbreeding grounds – but in males only.These findings provide a window onto the processes by which wetland salinity can induce carry-overeffects and can help predict how migratory species should respond to future climate-induced increasesin salinity.

Resolving the migratory connectivity (identifying non-breeding grounds) of migrating bird populations that are morphologically similar is crucial for an understanding of their population dynamics and ultimately their conservation. Such is the case in Black-tailed Godwits Limosa limosa, where the Iceland-breeding subspecies islandica shows overlap during the non-breeding season with the continental-Europe-breeding limosa. On the basis of variation in the control region of mitochondrial DNA, it was already shown that there is a cleat geographic structure in their phylogeography and a clear discrimination between the haplotypes of the two subspecies. We can thus assign subspecies of non-breeding individuals on the basis of a molecular assay. Here we validated this approach using samples of 113 birds with known breeding origin, and on the basis of haplotype variation, all birds were properly assigned to each subspecies. We then tested for overlap during non-breeding season using a sample of 278 birds from an Iberian wintering and staging area, the inland rice fields in southwest Iberia (Extremadura, Spain). We showed that even in this inland area, 6.5 % of the birds belonged to islandica subspecies, thus demonstrating the usefulness of genetic markers as an alternative or supplementary method to the most common approach, individual colour-ringing.

Resolving the migratory connectivity (identifying non-breeding grounds) of migrating bird populations that are morphologically similar is crucial for an understanding of their population dynamics and ultimately their conservation. Such is the case in Black-tailed Godwits Limosa limosa, where the Iceland-breeding subspecies islandica shows overlap during the non-breeding season with the continental-Europe-breeding limosa. On the basis of variation in the control region of mitochondrial DNA, it was already shown that there is a cleat geographic structure in their phylogeography and a clear discrimination between the haplotypes of the two subspecies. We can thus assign subspecies of non-breeding individuals on the basis of a molecular assay. Here we validated this approach using samples of 113 birds with known breeding origin, and on the basis of haplotype variation, all birds were properly assigned to each subspecies. We then tested for overlap during non-breeding season using a sample of 278 birds from an Iberian wintering and staging area, the inland rice fields in southwest Iberia (Extremadura, Spain). We showed that even in this inland area, 6.5 % of the birds belonged to islandica subspecies, thus demonstrating the usefulness of genetic markers as an alternative or supplementary method to the most common approach, individual colour-ringing.