East or West? Different populations of Red-necked Phalaropes use distinct migration routes

A study using geolocators uncovered a migratory divide in this wader species.

Choosing a holiday destination can be a difficult choice: a lazy beach holiday on the Canary Islands or an adventurous trip to east Asia? Birds face a similar dilemma when they embark for their wintering grounds. Should they fly east or west? In some species, different individuals use different migration routes. A classical example is the Blackcap (Sylvia atricapilla) in Central Europe: one part of the population migrates to the southeast, while the other part prefers the southwest. This phenomenon is known as a migratory divide. A recent study in the journal Frontiers in Ecology and Evolution uncovered a similar pattern in the Red-necked Phalarope (Phalaropus lobatus).

 

Two Migration Routes

An international team of scientists equipped several Red-necked Phalaropes from different populations with geolocators. The results showed two distinct migrations routes. Birds breeding in Scotland, Iceland and Greenland migrated to the west and wintered in the Pacific. Birds from Scandinavia, Finland and Russia, on the other hand, flew to the Arabian Sea in the east.

The birds that migrated west covered more distance (~10,000 km) compared to the birds that followed an eastern route (~6,000 km). This difference in migration distance is also reflected in their morphology. West-migrating birds had longer wings that were probably more pointed. This wing type is aerodynamically more efficient for longer migration.

Geolocators uncovered different migration routes for different Red-necked Phalarope populations. From: van Bemmelen et al. (2019) Frontiers in Ecology and Evolution

 

More Differences

Once at the wintering grounds, the birds also behaved differently. Red-necked Phalaropes wintering in the Arabian Sea moved between several areas, while birds wintering at the Pacific Ocean remained roughly in the same area. What causes this difference remains to be investigated, but the distribution of food sources seems a plausible explanation.

 

Hybrids?

One aspect that the study did not address concerns possible interbreeding between the different migratory populations. In the Eurasian Blackcap, hybrids between populations with different migration routes head in an intermediate direction: straight to the south. This suggests a strong genetic component for migratory behavior. Whether the same is true for Red-necked Phalaropes is unknown, but I would love to find out…

A Red-necked Phalarope at Blackwater National Wildlife Refuge (Maryland, USA) © U.S. Fish and Wildlife Service Headquarters | Wikimedia Commons

 

References

Helbig, A. J. (1991). SE‐and SW‐migrating Blackcap (Sylvia atricapilla) populations in Central Europe: Orientation of birds in the contact zone. Journal of Evolutionary Biology, 4(4):657-670.

Minias, P., Meissner, W., Włodarczyk, R., Ożarowska, A., Piasecka, A., Kaczmarek, K., & Janiszewski, T. (2015). Wing shape and migration in shorebirds: a comparative study. Ibis, 157(3):528-535.

van Bemmelen, R.S.A., Kolbeinsson, Y., Ramos, R., Gilg, O., Alves, J.A., Smith, M., Schekkerman, H., Lehikoinen, A., Petersen, I.K., Þórisson, B., Sokolov, A.A., Välimäki, K., van der Meer, T., Okill, J.D., Bolton, M., Moe, B., Hanssen, S.A., Bollache, L. Petersen, A., Thorstensen, S., González-Solís, J., Klaassen, R.H.G & Tulp, I. (2019). A migratory divide among red-necked phalaropes in the Western Palearctic reveals contrasting migration and wintering movement strategies. Frontiers in Ecology and Evolution, 7:86.