Genetic Variation and Migration of Waders

The migratory behaviour of birds has received much scientific interest, though many questions still remain unsolved. One of the reasons for this is the difficulty of following the birds as they move between breeding and wintering localities. Populations may mix on migration and the origin of individual birds is difficult to assess. One way to address this problem may be to develop genetic population markers, using molecular genetic analysis to estimate the breeding origin of the birds, and thereby making it possible to recognise them throughout the annual cycle.

In this thesis, the genetic variation in three wader species is studied: Dunlin (Calidris alpina), Curlew Sandpiper (C. ferruginea) and White-rumped Sandpiper (C. fuscicollis). Waders are among the most long-distance migrants and often travel many thousands of kilometres every spring and autumn. The genetic variation within these species is described mainly using two molecular genetic methods: DNA-sequencing and microsatellite analysis.

In the Dunlin, the mitochondrial control region shows clear geographic structuring on a global geographic scale, however some overlap also exists between populations. Geographic structuring is also found by microsatellites, which show more variation and also indicate genetic differences between populations on a local scale. Genetic markers are applied in two studies of the migration strategies of Dunlin, showing a parallel migration system, estimating the migration distances, and showing variation within the species in the timing of breeding, migration and moult.

The Curlew Sandpiper, on the other hand, shows almost no geographic structuring and seems to have extremely low genetic differentiation between the two extreme flyways to West Africa and Australia respectively. Also the White-rumped Sandpiper shows genetic similarities between distant breeding areas. The low levels of genetic variation and population structuring in high arctic waders may be related to the influence of the glacial cycles on the breeding habitat, as well as to their migration strategies.

Another method for identifying the origin of migrating birds may be to use of isotope analysis. White-rumped Sandpipers from different breeding grounds had different carbon isotopes ratios in the feathers, thus isotope analysis make it possible to distinguish them also on migration.