Tanguar Haor – a legendary wetland

IMG_0414There’s no business, like duck business

This spring I have been going places. First Bangladesh, and then Ukraine. Both trips connected by ducks, and the hopes of using telemetry to infer migratory connectivity of waterfowl populations and the transmission risk of avian influenza viruses.

Together with our colleagues at IUCN Bangladesh we spent some magnificent weeks in the wetlands of northeastern Bangladesh catching wintering ducks. I am writing up a longer piece of this trip for Birdlife Sweden’s magazine Vår fågelvärld which I hope to share with you in a couple of months. In the meantime, I’d like to refer you to an excellent article by Abida Rahman Chowdhury, a journalist from The Daily Star who visited us in the field in Tanguar Haor – the gem of wetlands in the north. Please read it on this link.

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.

 

Ducks of the corn

Our research shows that there are many scary things lurking in the cornfields. (The Mallard head source, under a CC BY 2.0 license; rearranged by M. Wille).

Our research shows that there are many scary things lurking in the cornfields. (The Mallard head source under a CC BY 2.0 license; rearranged by M. Wille).

By Jonas Waldenström

The Mallard is the most widespread and abundant duck in the world. It inhabits almost any type of water body, from the shores of great open lakes, to the smallest ponds. Most people don’t really notice them; they are just there. (One exception here on the eco-evolutionary dynamics’ blog).

Our negligence of Mallards should not be taken as they are unimportant. On the contrary, they are important parts of the food web, as consumers of invertebrates and seeds, and providers of juicy dinners for aerial raptors such as Peregrine falcons and White-tailed Sea-eagles. They make good food for mammals too – many a fox has dined on Mallards eggs, and we ourselves shoot them in large numbers. Very large numbers.

In our research we are interested in Mallards as hosts for diseases, especially the influenza A virus. We have studied virus carriage in great detail over the last 12 years and are now trying to connect the various pieces to a coherent epidemiological picture. However, one part of the puzzle has been largely neglected until now: their stopover ecology.

Yes, Mallards are migratory, especially the populations that live on northern latitudes . The ducks we trap at our field site originate from the Baltic states, Finland and Russia, and migrate predominately to southern Denmark and northern Germany. Daniel Bengtsson in my lab works on Mallard ecology, focusing on what the ducks do when they are on stopovers during migration.

Mallards are relatively heavy birds, with an average body mass of just below one kilogram. Migration is taxing and requires a lot of energy, and with the heavy bulk the Mallards don’t fly the whole distance at once; rather they make several bouts of migration interspersed with longer stays at suitable stopover sites.

So what do the ducks do all day, and all night? A seemingly straightforward question. During daytime we can watch them with binoculars and note their behaviors. But it turns out they don’t do very much. A typical Mallard in an autumn day in November does pretty much nothing more than sleeps, poops, and preens its plumage. Pretty dull. Occasionally it may dabble a little in the murky water, but on average they are just chilling.

This makes sense from a prey perspective: if you are a juicy meal you should stay in groups and divide the predator scouting among individuals. The talons, beaks and jaws are always ready to take a piece of you. However, at the same time a duck needs to replenish the energy stores in order to finish migration. So if you don’t feed much at day, you have to do it at night.

Together with colleagues in Germany and Sweden we have started to tap into the whereabouts and behaviors of Mallards during migration. At our aid we have modern telemetry gadgets that help us track the birds remotely. Last week we published a paper in PLOS ONE with the latest results.

A Mallard ready for departure (Photo D. Bengtsson)

A Mallard ready for departure (Photo D. Bengtsson)

We equipped wild-caught Mallards with small GPS-transmitters, fastened on the back of the birds as little rucksacks. These devices took a GPS fix every 15 minutes, thereby allowing us to see where the birds moved, and when. However, in order to get the data we first needed to find the birds in the field and then download the data with a receiver on a radio link. The best way of doing this was to make daily flights in a light airplane, gently soaring amidst the clouds until the receiver made a ‘beep’, signaling that it located a duck. On days with bad weather the plane could not be used; instead we trudged through kilometers of shoreline on foot.

In the paper we analyzed movement patterns and habitat use of 16 individuals followed across a couple of weeks. During daytime the ducks behaved just as I said before – they didn’t move much at all. But when dusk fell all birds got on their wings and flew inland, sometimes quite long distances. Each duck seemed to follow its own nightly routines, but it was also evident that some ducks followed other ducks around. A typical night would consist of a first flight from the coast to an agricultural field, most often harvested cornfields. In the fields they would settle for a short while, often less than an hour, likely stuffing their crops full of leftover corn, before embarking on another flight out to various inland water bodies. In these ponds and wetlands they spent the reminder of the night. Just before dawn, the flight would go in the opposite direction, including a short stay in the cornfield, before settling down on the coast again.

An airial view of the study site. Ducks chill by the coast at day and fly out in the agricultural landscape at night (Photo D. Bengtsson)

An airial view of the study site. Ducks chill by the coast at day and fly out in the agricultural landscape at night (Photo D. Bengtsson)

Example of typical mallard movements between frequently used sites on southeast Öland, Sweden, October – December 2010. Inset A: Orange ovals = coastal meadows; yellow ovals = maize fields; red ovals = flooded areas; blue ovals = coastal day-roosts; green ovals = coastal reefs used as day-roosts; grey circle = duck trap location. Inset B: Yellow oval (1) = maize field visited during dawn and dusk; red ovals (2) = various small (flooded) wetlands on alvar steppe (the upper one reaching into a maize field), visited at night; green oval (3) = coastal reef used as day-roost. Inset C: Yellow oval (1) = two maize fields frequently visited, mostly during dawn and dusk; red oval (2) = flooded area (stream) visited most nights; light purple oval (3) = flooded pasture visited during two consecutive nights (probably for feeding); blue oval (4) = most frequented day-roost. From the article in PLOS ONE, under CC Attribution License.

Example of typical mallard movements between frequently used sites on southeast Öland, Sweden, October – December 2010. Inset A: Orange ovals = coastal meadows; yellow ovals = maize fields; red ovals = flooded areas; blue ovals = coastal day-roosts; green ovals = coastal reefs used as day-roosts; grey circle = duck trap location. Inset B: Yellow oval (1) = maize field visited during dawn and dusk; red ovals (2) = various small (flooded) wetlands on alvar steppe (the upper one reaching into a maize field), visited at night; green oval (3) = coastal reef used as day-roost. Inset C: Yellow oval (1) = two maize fields frequently visited, mostly during dawn and dusk; red oval (2) = flooded area (stream) visited most nights; light purple oval (3) = flooded pasture visited during two consecutive nights (probably for feeding); blue oval (4) = most frequented day-roost. From the article in PLOS ONE, under CC Attribution License.

A postdoc in our lab summarized this study as “ducks like water, and food”. Although correct, I think we could say a number of other things. Firstly, we could estimate how large home ranges the ducks were utilizing, and that they very selectively chose cornfields (which comprised only a minority of the arable land in the study area). Secondly, we could show that the omnivorous Mallard is flexible in diet selection, as corn (intended for winter fodder for cattle) is a new crop in the area, and that this happens already in inexperienced juveniles during first migration – in fact, corn isn’t a much grown crop in the recruitment areas. Thirdly, our data suggests that the ducks balanced intake of corn with predation risk, trying to minimize the time spent in open fields. Knowing these things adds to our understanding of the connection between wildlife and agriculture, especially important for the Mallard,  a prime reservoir for influenza A virus that can infect domestic poultry.

Link to the article:

Bengtsson, D., Avril, A., Gunnarsson, G., Elmberg, J., Söderquist, P., Norevik, G., Tolf, C., Safi, K., Fiedler, W., Wikelski, M., Olsen, B. & Waldenström, J. 2014. Movements, Home-Range Size and Habitat Selection of Mallards during Autumn Migration. PLOS ONE 10.1371/journal.pone.0100764

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