Ducks lost and found

Waiting at the shoreline (Flickr CC BY 2.0)

Tracking birds is a rollercoaster ride between excitement and disappointment. Even though the technology is improving rapidly, some loggers will fail anyway, some birds will be taken by a predator, and some birds just don’t do all the exciting things you hoped they would. But on the other hand, when everything works you get extremely detailed knowledge about the behavior of individual birds across the annual cycle.

Given this, and the cost of each logger, there is always that moment on the shoreline. You see the bird (in our case a duck) fly, very rapidly away and the question of what will happen next forms in your mind. Will we learn anything about its life, will we see it again? Have we interfered too much in its life?

Over the years we have learned a bit on the rough life of ducks. A number of ducks have been shot by hunters, either reported by the hunters or detected by logger movements in cars and fixes on farmsteads. Quite a few we believe have been killed by predators, including a northern pintail that was taken by a goshawk within two hours of deployment and a mallard eaten by a fox in eastern Germany. On top of that we have adverse weather events, such as cold spells and blizzards that take they their toll on wintering birds.

One particular problem is when a bird reaches an area where the logger no longer has connection and can not send data. The bird is gone, vanished from the map. This is especially evident for two of our study species, the Eurasian wigeon and the northern pintail. Both species breed in large numbers on the tundra, far away from human settlements, in areas where mobile phones do not work. Thus, there comes a time when the signal is lost, and you can only hope the bird will return and send data again sometime later.

For our wigeons, we had seven birds that were lost this summer: Nicola in Murmansk, Sarah in eastern Finland, Fitzwilliam in the Pechora river in Russia, and Michelle, Sita, Ellinor and Pär east of the Ural mountains. But in the last week we have reconnected with Sarah in Archangelsk and Fitzwilliam in Estonia, and hopes are we will get reconnected with some of the others.

Until then we are waiting at the shoreline.

Fitzwilliam the wigeon: he once was lost, but now am found

Linnaeus goes Motus

It is already mid-October, but the weather is still mild for the season, especially so the last couple of days. Today we took advantage of the sunny autumn day and headed up on the roof. And what splendid scenery there is on top of the new university building! You can see tens of kilometers in each direction and have a clear view of the strait of Kalmar. A perfect spot to place our new MOTUS antennas.

And what is a Motus antenna, you may ask? Good question. The Motus Wildlife Tracking System is a collaborative research network that uses coordinated automated radio telemetry arrays to study movements of small animals. Or simply put: you can equip birds with mini radio transmitters and listen for them with large radio antennas. And by placing many antennas in a flyway of birds, you can follow the birds during migration. This is a big thing in North America, and just recently have started to become more common in Europe. If you look at the maps below you see that the towers currently are focused to the Wadden Sea region, but with occasional towers elsewhere. Together with Ottenby Bird Observatory and Lund University we are now building a network of Motus towers on the island Öland.

Compared to other tracking techniques, Motus has the benefit of really, really small loggers – all the way down to 0.2g. This means you can put them on smaller birds compared to other types of loggers, and study migration of warblers, thrushes, swifts and waders. And the more towers the better, as all towers can detect all loggers and forward the data to the right project. Pretty nice! Thus, today we added a new tower to the system.

 

Duck (and virus) movements from afar

A wigeon track on the undulating tribituary of the Pechora river

Before I was a researcher, I was a birder. I spent my free time either birding, or thinking about birds. And my favorite place was Ottenby Bird Observatory. This is where my formative years took place and where I made friends for life. A focus point in my existence to this day. I spent countless mornings ringing birds at the observatory. Sleep deprived, sustained by coffee, sandwiches and tobacco we young ringers often talked about what would happen with the birds we released. Where would they go, what would they do? We marveled about the epic journeys they would undertake, connecting distant parts of the globe.

Sometimes we got answers, for one benefit of ringing is that the rings transform birds into individuals, and hence make possible to follow if they are trapped again, resighted or found dead. The downside is that these are all rare events, especially for smaller birds. For instance, the chance of getting a ring recovery of a willow warbler on wintering grounds in East Africa is very low, somewhere around 1 out of 100,000 ringed birds. For other birds like the mallard, the chance of a recovery is closer to 10% – a considerable difference. In any case, the information you get is limited and usually shown as a dot on a map.

But times have changed. I am older, greyer and possible wiser, a professor working with bird borne infections (but not birding as much as I would like to). I am still very interested in the question of where birds go, and what they do. Fortunately, tracking technology has taken giant leaps and we can now do studies that were unheard of when I was a young ringer. In recent years, my laboratory has been involved in studies investigating movement behavior of mallards. Together with Martin Wikelski’s team in Constance, we have looked at home range sizes and habitat selection of mallards during migratory stopovers, tested the hypothesis that influenza A virus infection impairs movements of mallards, and even made translocation experiments between Sweden and Germany to repeat Perdeck’s classic starling study. We have used Argos loggers, radio-frequency loggers and GSM-loggers, and for each study the loggers have become better and lighter and data ever more detailed.

Right now, we are a part of DELTA-flu, a Horizon2020 EU-project with several European partners. Our role is to investigate the migratory connectivity of waterfowl in Eurasia in light of HPAI virus transmission. Can we use loggers to answer the question about possible routes of virus transmission across continent?

An urban mallard in Roskilde, Denmark, presently hanging out on the Roskilde Festival camping site

The loggers we use come from the company Ornitela in Lithuania, and weigh 10, 15 or 25g depending on which duck species we target. The general rule of thumb is that a logger shouldn’t weigh more than 3% of the bird’s mass, as not to impair it unnecessarily. These loggers are little marvels; they transfer data via the mobile phone network and can be programmed remotely. So far we have deployed loggers in Sweden, Lithuania, Netherlands and Georgia, and are planning to work in Ukraine, South Korea and Bangladesh. We are also waiting for the next leap in telemetry: the ICARUS project onboard the International Space Station. With this technology, loggers may reach 2.5g and hence be put on a larger range of species. What all these loggers do is to provide a real-time window into birds’ movements: Where they are and what they are doing, sometimes even what they avoid or what caused their deaths. We can follow the lives of ducks in great detail.

There is a veritable flood of data, with more than one million GPS points collected already. It is easy to get lost in time just watching the latest whereabouts of the tagged ducks, from the tundra regions east of the Ural mountains to a gravel pit outside Bremen. I hope to write here more frequently, because there is a lot of exciting stuff happening in the lab at the moment – until then, have fun!

Flu, ducks and the costs of being infected

IMG_4978

There was light snow this morning, but it has since melted away, leaving small puddles on the streets. Unfortunately, the sun seems to have lost today’s battle with the fog and the low clouds – it is, in essence, an ordinary wet, cold and gloomy February day. But if I peer out through the window, ignoring the construction works in the foreground, there is water on the horizon. And where there is water, there are ducks. And where there are ducks, there is flu. One cannot ask for more.

Over the years I have thought much about ducks and flu. (Some would say too much, but they don’t know what they miss). Although my research group has already produced four PhD theses on this topic, there is so much more that I would like to know. Some of it is  highly specialized knowledge, of interest for a limited set of like-minded scientists with  acquired duck disease tastes. Other things are quite basic, but hard to study, such as the question whether ducks infected with flu suffer from infection or not. That is a pretty important question also for a broader audience, as it has relevance for how well virus can spread with individuals in the environment; especially how ducks may spread virus long distances during migration. So, do they suffer from infections, or not?

Actually, there has been some controversy on this topic – partly stemming from different methods of quantifying disease effects. A field ecologist and a veterinarian have different scales in their toolboxes, one could say. In the latter case, disease signs are determined in  experimental infections in animal house facilities, where individuals can be followed over time. Such experiments in Mallards have not been associated with strong disease signs – as long as we consider the low-pathogenic avian influenza viruses that are naturally occurring in wild avian populations (highly pathogenic AI is a completely different story). Infected Mallards shed viruses, but are otherwise apparently healthy, or only display a very short increase in body temperature. But, the ecologist argues, the artificial environment with plenty of food, controlled temperature and absence of predators is not really mimicking the situation in the wild, where even small reductions in vigilance and movement capacity may end in the death from a raptor’s claw. Absence of overt disease is not equal to absence of ecological costs, the ecologist would conclude.

The field studies so far have been a mixed bag, ranging from large effects to negligible effects depending on study and the species considered. The largest effect was seen in a study of Bewick’s swans in the Netherlands, where infected birds had poorer condition and migrated slower than uninfected swans. Such large effects have not been seen in other species, and one can not conclusively rule out other underlying factors, as the swan study was based on a limited number of birds. When it comes to Mallards – the most glorious of all avian influenza reservoir species – previous population studies from our group have suggested infected birds to weigh on average less than uninfected birds at capture.

Averages and populations are all and well, but to get to a mechanistic understanding one is better off with experiment conducted on a set of individuals. However, a problem is that we can not infect birds and release them in the field; in fact, we are not allowed to do so – there is a reason infection experiments are conducted in biosafety labs, after all. What to do, then? Well, we approached this question via GPS and accelerometer loggers attached to two groups of birds caught during the ongoing surveillance at our study site: one group of 20 Mallards with natural avian influenza infection at the time of capture, and another group of 20 Mallards that were negative for influenza at the time of capture.

The benefit of these data loggers is that they record such a wealth of information. From the GPS fixes we can follow the birds in the landscape and quantify their movements at spatial and temporal scales; from the accelerometer we can get metrics that describe activity, defined as movements in the x, y, z-dimensions. We predicted that infection would significantly hamper movement, and that with time the difference between infected and uninfected birds would level off (see figure below); hence the analyses need to take time in to account, too.

F1.large

Theoretical predictions of the influence of infection on movement metrics. If infection affects spatial behaviour, infected (blue) and uninfected (red) birds should behave differently at the time of release. We postulate that, at this time, movement metrics for infected birds should be lower than for uninfected birds, which would be revealed as different intercepts of the regression of the movement metrics against time for uninfected (β0) and infected birds (β0+βInf). As infected birds recover with time, their movement metrics will approach and eventually meet the values for uninfected birds. This happens when the slope of the regression of the movement metrics against time for infected individuals (βT.aft.Rel*inf) reaches the slope for uninfected birds (βT.aft.Rel), which is expected to be null.

The full paper is freely accessible at Royal Society Open, and I hope readers with a more heavy interest in movement ecology download and read it. There is a lot of data crunching and statistics there that most of you are likely not that interested in – if you are, go read the original publication – but remember even easy questions may be hard to answer. Okay, with that said, what where the results?

Well. There were no effects of infection on the movement parameters measured, at all. Yes, there were differences among individuals, and between night and day, but infection status did not explain much of the variation in movement metrics. This means that under the natural situation in this study, conducted during stopover in autumn migration, infected ducks moved as much as uninfected ducks. This also means they likely are not impaired by infection during active migration, and could therefore carry LPAI viruses on the wing as they depart the stopover site.

Is this, then, the last nail in the ‘cost of infection’ coffin for low-pathogenic influenza in ducks? Probably not, because one could argue that non all viruses behave the same (in fact, there should be a variation for virulence), and that some viruses may have adapted to infect non-mallard-birds, and hence be spillover infections in Mallards (and then potentially be at less than optimal virulence). Moreover – and perhaps a stronger argument – there may be differences in outcome depending on whether it is a primary infection, or subsequent infection; where the first infection in a naïve bird could be believed to carry a larger cost. Or there may be effects seen only at certain environmental conditions.

All these ‘but, or, perhaps, mayhaps’ are classic scientist disclaimers… My personal belief, these days, is that also the ecological costs of infection are slim. But I am happy to be proven wrong – out you go now and study.

There is water at the horizon still. And questions aplenty.

 

Link to the article:

Bengtsson, D., Safi, K., Avril, A., Fiedler, W., Wikelski, M., Gunnarsson, G., Elmberg, J., Tolf, C., Olsen, B. & Waldenström, J. 2016. Does influenza A virus infection affect movement behaviour during stopover in its wild reservoir host? Royal Society Open Science 3: 150633.

 

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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Perdeck revisited – or how well does a Mallard know its way?

By Jonas Waldenström

At this time of the year the air is full of migrating birds. Some, as cranes or geese with their conspicuous formations are easily spotted with the naked eye, while other birds, including most smaller songbirds, fly at altitudes where you need a scope to see them. But you can often hear them; each species has its own tune, and an experienced ear can tell them apart on call alone.

The question “how do they find their way” is as old as the field of ornithology itself. Generally, migration wouldn’t be possible without some sort of compass; a way of telling the bird in which direction to move. It has been shown that birds may use the sun, the stars, and the earth’s magnetic field for assessing their heading. And in some species also visible cues, a sort of map sense from previous travels, or even olfactory cues (a posh word for smelling where home is). As the vast majority of birds migrate without the guidance of their parents (which seems reserved to some flock-living species), a juvenile bird must be born with not only the tools to assess where it is, but also a sense of where it should go.

One of the pioneering fathers of ornithology was the Dutch professor Albert Christiaan Perdeck. He made one of the first real tests on how birds can sense where they are going, and how they can adjust the course if they get out of track. In order to test this he wanted to do a displacement study, where birds should be experimentally transported to a novel site, far from the catching site. As this study was conducted in the 1950s, in the pre-gadget era of ornithology, he needed a species that he could catch in large quantities, and where ring recovery data could be collected. His choice of study animal was the European Starling Sturnus vulgaris, a common farmland bird in most of Northern Europe. Starlings in autumn can aggregate in huge flocks, sometimes consisting of several thousand individuals, and was thus a good target species for Perdeck.

With a remarkable enthusiasm, the team caught and ringed thousands of starlings. Some were released at the ringing site in the Hague, while the other half were transported with airplanes to Switzerland and released. After some time the ring recoveries started to come in, and the results were extremely interesting. It seemed as the young starlings had a vector compass, as the birds that were transported south stayed on the same heading as they had when they were caught. But instead of ending up in Holland, the young starlings ended up way south, sometimes even on the Iberian peninsula. I wrote ‘young’ deliberately, as there was a clear age effect. Where the juvenile birds continued on the same vector, the adult starlings compensated for the displacement, changed course and headed to the original winter quarters. Adult birds are more experienced, and in the starling case they were able to adjust to the circumstances and get back on the right track. A quite remarkable feat – some of my colleagues cant find their way to the university canteen without a helper…

Spurred by the old studies (classics, you could say) and the advancement of new tracking tools we conducted a similar experiment with Mallards. The study was a collaborative effort with scientists from Sweden, Germany, the UK and Denmark (with the lead from Professor Martin Wikelskii at the Max Plank Institute for Ornithology, in Constance, Germany). Today’s gadgets can do stuff Perdeck could only dream about. During two autumn seasons, we caught juvenile Mallard females at Ottenby – our beloved duck field site – and equipped a total of 76 birds with satellite GPS transmitters. Half of the ducks were released at Ottenby, and the other half were transported in a private airplane to Lake Constance in southern Germany and released there. The tags had solar panels and, in the best of circumstances, had the potential to send data for at least two years; providing highly accurate GPS fixes at several times a day.journal.pone.0072629.g002

However, the best of circumstances is not often met in nature. The tags on the birds in Ottenby had problems with the lack of sunshine during Swedish late autumn and winter, and many of them just went offline. But a fair number of tags delivered data on movements both in autumn/winter and in spring, when birds headed to their breeding grounds. Contrary to the Perdeck’s starlings, our displaced Mallards did not continue migration in autumn; they stayed in the Lake Constance region. Of the Mallards released at Ottenby, some continued migration to the general wintering area of our study population, that is Denmark and Germany, south to The Netherlands.

After the winter: “most of the translocated ducks headed straight north-north-east, as if heading towards Ottenby, with one duck going as far as northern Sweden. Three of the transported ducks, however, first headed in a more easterly direction and turned northwards when reaching the longitudes of the area the control birds migrated to. It is unclear how these birds decided when to turn north, but the movement trajectories could be interpreted as if individuals had noticed that they were in the wrong place and then corrected for the southward translocation. Based on the observation that this second group of transported ducks ended up in their potential natural breeding grounds, and the first group had a more northerly heading than the control group, we conclude that mallards, just like the starlings from Perdeck’s original experiment, can correct for translocation during the spring season following the experiment.journal.pone.0072629.g004

Thus, there was quite large differences between individuals in the translocated group, from those that seemed to take the shortest route north to Ottenby in spring, to those that followed a eastern direction (and then going north), more in the direction of what they should have had if the stayed in the normal wintering grounds: a flexibility in continental navigation and migration.

The article is open access and can be found here.

As the Mallard flies

By Jonas Waldenström

Migratory animals are per definition mobile, performing regular movements between areas. Sometimes such movements are small, as in up or down a mountain. Other times they involve crossing 11,000 km over open sea, as the Bar-tailed Godwits do on their migration from Siberia to New Zealand.

Not exactly a rocket

Not exactly a rocket

Our model species is the Mallard. It is not exactly a rocket or a Godwit. No, it is a bulky and rather heavy bird, not designed for enduring intercontinental flight. But it does fly, and fairly decent distances. From band recoveries and analyses of stable isotope contents in feathers, we know that the breeding areas are for Mallards passing Ottenby in autumn can be roughly outlined as the Baltic States, Finland and parts of Eurasian Russia. Winter areas are more easily depicted, as a lot of ducks are harvested by hunters and the number of bands reported back during non-breeding is high.

But a dead duck is an endpoint, and doesn’t tell us much about its behavior before (or after) it was shot. As Mallards are an important reservoir host for influenza A viruses we want to know more about what movements actually mean for the epidemiology of disease. Does infection impair movements? Can infected birds transport viruses along migration to other sites? How does that affect local and global transmission?

A few years ago we started to collaborate with Martin Wikelski and his research group at Max Plank Institute of Ornithology in southern Germany. His group is a leading group on research in movement ecology, experts in animal movements. It is really a cutting-edge discipline, as new techniques for following animals are constantly developed. A lot of new cool gadgets!

Together with our German colleagues, we have carried out a number of studies with tagged Mallards, equipped either with satellite transmitters or with GPS loggers. There are a few articles in the tube, and Daniel Bengtsson, one of my PhD students, has Mallard movements as his subject area. The very first article on Ottenby Mallards appeared recently in Movement Ecology. Actually in the very first issue of the journal!

In this study, Kamran Safi gathered movement data from nine different species of birds (including our Mallards) and used it to analyze how the effect of wind support during migration best should be modeled. Completely still air is rare, and migrating birds need to adjust migration to wind strength and wind direction. A tail wind component can be extremely beneficial, and headwinds detrimental. With the modern tags birds can be followed at high sampling frequencies (at the scale of minutes and hours) during active flight, and their heading and speed can be examined in conjunction with global weather databases. But it is crucial that you used the right models, otherwise you may end up with the wrong conclusions.

2051-3933-1-4-1

Schematic representation of the calculated measures, where α represents the vector of a bird’s movement relative to the ground. Its length is vg. Wind support (ws) is the length of the wind vector in the direction of c and cross-wind (wc) the length of the perpendicular component. Finally, airspeed (va) is the speed of the bird relative to the wind and can be calculated as given above, or modeled as the intercept of a model with vg as a function of ws and wc.

Perhaps not surprising, Safi et al found that wind was a strong predictor of bird ground speed, but with variation among species. However: determining flight direction and speed from successive locations, even at short intervals, was inferior to using instantaneous GPS-based measures of speed and direction. Use of successive location data significantly underestimated the birds’ ground and airspeed, and also resulted in mistaken associations between cross-winds, wind support, and their interactive effects, in relation to the birds’ onward flight.

It is rather complex paper if you are not into the field, but it feels good that our flu-carrying little duckies can contribute with some pieces of the puzzle in the making of next generation migration models. We will return to Mallards and movements in this blog in the future, as the Mallard flies and the papers become published.

Links to the papers:

Safi et al 2013 Movement Ecology

Gunnarsson et al 2012 PLoS ONE