Pathogen tea bags, golden orioles and climate change

By Jonas Waldenström

Close your eyes and let your mind wander. Try to imagine the most beautiful place you can think of, fill it with scents and colors, let flowers blossom and birds sing, let there be volcanoes and old ruins! And let there be food, rich wonderful food, and wines that make your heart sing! Where would that be? What kind of paradise is that? The answer is simple: an Italian island in April and May! There are few places on this planet that are more endearing than the Mediterranean coast in spring, where the wing beats of history are present in the landscape itself, and where the stunning orioles and bee-eaters make any birder go bananas!

Recently, I wrote a post on how biologists are obsessed with grim, dirty and tedious fieldwork – the worse the better! I poured a lot of wisdom in that text and have received a share of acknowledging nudges from colleagues. However, in science all normal distributions have outliers, be it the trunk length of elephants, dunnock testis size, or the harshness of fieldwork. Thus, admittedly, if there is fieldwork that is grim, there must be fieldwork that is agreeable, perhaps even wonderful. The most extreme outlier is the fieldwork conducted on Italian islands.

The particular island for this story is the island of Capri. This gem is situated in the mouth of the bay of Naples, with Ischia and Proscida as closest neighbors in the north, and Sorrento and the Amalfi coast to the south. Capri has been inhabited for a very long time, perhaps as far back as the Bronze Age. The Roman emperor Augustus started to develop the island, and his successor Tiberius continued and built several villas on Capri. Ever since the Romans, Capri has been the home for the rich and famous – and lately to a few Italian and Swedish researchers. To get to Capri you either have to sail your own yacht, or you take the ferry from Castello d’Ovo in Naples to Marina Grande on Capri. Once ashore, the island is towering high above you, reaching some 580 m in altitude at the highest peak. From Marina Grande you need to transport yourself to the village of Anacapri, on the plateau on the western part of the island.

Villa San Michele is a piece of serene beauty. From Wikimedia Commons

Villa San Michele is a piece of serene beauty. From Wikimedia Commons

Anacapri is a very pleasant Italian town, with several restaurants and cafés, but we are not stopping yet. The goal for our imaginary travel is just a little further bit ahead. From the piazza you need to walk along Via Capidimonte together with the large crowd of tourists that are heading to Villa San Michele – one of the island’s most famous attractions built by the eccentric Swedish physician Axel Munthe. Through the locked gate in the villa garden we take the winding path to the top of the mountain. There at the summit lies Castello di Barbarossa, the remnants of the legendary pirate Red-beard’s castle. The view is stellar! On one side there is a 300 m fall, and on the other side a more gently declining hillside covered in macchia vegetation. Welcome to Capri Bird Observatory!

Axel Munthe bought the old castle and the mountaintop in order to give birds a shelter during migration. Hunting of birds was a large operation at Capri in those days, and still is in some parts of Italy today. Axel Munthe pitied the animals and took a strong stand against hunting. When he died, the Villa and the mountain were given to the Swedish state and in 1956 the first Swedish ringers visited the island and started the observatory. Since 20-30 years the site is run by Italian ringers as a part of their island project ‘Progetto Piccole Isole’.

Yes, that's the castle! Photo Magnus Hellström

Yes, that’s the castle! Photo Magnus Hellström

It is truly the best field site in the world. Not only is it strikingly beautiful, it is also a place where you can do great science. In April and May the island can receive large downfalls of migratory birds, particularly songbirds, that have crossed the Mediterranean Sea over night. At times there are birds everywhere, in all colors and sizes, from Willow Warblers, Whinchats and Tree Pipits to Quails and Scoops Owls. Traditionally, bird ringing has been more commonplace in Northern and Western Europe and the trapping series at Capri is in fact the longest available from the Mediterranean area. A few years ago we collated the data from Capri with similar data from Scandinavian bird observatories and analyzed long-term trends in the timing of migration. This data, published in Science, showed that the tropical migrants arrived earlier to the breeding areas as a response to an earlier spring, but that the major shift was a more rapid migration through Europe, and not an earlier arrival at the Mediterranean region.

The flying banana - the Golden Oriole. During migration you see flocks of this stunning bird at Capri. Image from RSPB

The flying banana – the Golden Oriole. During migration you see flocks of this stunning bird at Capri. Image from RSPB

In recent years, a team of Swedish researchers has visited the castle together with the Italian ringers. But this time it is not the birds that are in focus, but the ticks the birds are carrying. Ticks are the ultimate pathogen vector, a cosy teabag for a variety of blood-borne viruses and bacteria, some which are very virulent to humans. Inside the tick the pathogens can survive and get transported to a new host without exposing themselves to the harsh outside environment. Some pathogens can even multiply within the tick, thus utilizing the arthropod as an intermediate host.

After a few field seasons, and the labor of an army of students in the lab, the publications are starting to emanate. Just a week ago, we published one survey of West Nile virus from Mediterranean ticks in Infection Ecology and Epidemiology Journal. This study was mainly a report of negative results, but a year ago we published a paper in Emerging Infectious Diseases on the findings of Crimean-Congo hemorrhagic fever virus (CCHF), and more analyzes are due to be published soon. The ticks are truly pathogen arcs, and birds potentially important for long-distance dispersal of diseases.

Thus, the heritage of Axel Munthe lingers. And in the distance Vesuvio sleeps.


Hagman, K., Barboutis, C., Ehrenborg, C., Fransson, T., Jaenson, T.G.T., Lindgren, P-E., Lundkvist, Å., Nyström, F., Waldenström, J., & Salaneck, E. 2014. On the potential roles of ticks and migrating birds in the ecology of West Nile virus. Infection Ecology and Epidemiology 4: 20943

Lindeborg, M., Barboutis, C., Ehrenborg, C., Fransson, T., Jaenson, T.G.T., Lindgren, P-E., Lundkvist, Å., Nyström, F., Salaneck, E., Waldenström, J. & Olsen, B. 2012. Migratory birds, ticks, and Crimean-Congo hemorrhagic fever virus. Emerging Infectious Diseases 12: 2095–2097.


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