Paper on parasite infection and migration patterns in barn swallows
Staffan Bensch and collegues (von Rönn et al.) has just published a new paper in Journal of Evolutionary Biology:
In this study of barn swallows we first used feather stable isotope ratios to confirm, what is well known from ringing data, that north European breeding populations winters in savannah-like habitats in Southern Africa, whereas Southern European populations winters in more moist regions of Western and Central Africa. Hence, swallows in northern Europe migrate almost twice the distance between breeding and winter quarters as compared to southern populations. Interestingly, the two migratory strategies occur together in swallow populations breeding in northern Germany. Within the same colony of swallows, one would assume that those birds with a shorter migration would have an advantage in terms of survival and early access to nest sites compared to those with a longer migration. But the feather stable isotope data showed that those taking the shorter migration distance to the moist regions of Western and Central Africa were more often infected with malaria parasites when they came back to their breeding sites than those that had spent the winter in the dryer southern parts of Africa. These results suggest that variation in infection risks in potential wintering areas can select for different migration strategies and help us understand the diversity of migration patterns observed in migratory species.