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.

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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

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Unlikely intrigue of tissues

By Michelle Wille

Most of us here at the Zoonotic Ecology and Epidemiology group have an interest in birds. Some of us are bird encyclopedias with an expansive knowledge of species names, identification, calls, etc, while others have a passing interest in identifying the species that inhabit our gardens. Those of us working on flu are rather focused on Mallard, which is our study species. At our study site, Ottenby, there are Mallard individuals that are resident, those that are migratory from the Baltic states, and those that come from father afield (ie. Russia). Most of our interactions with these birds are rather brief – weight, ring, swab sample, and maybe a blood sample. Regardless of the number of Mallards I have had the opportunity to handle, I often marvel at their beauty, especially the males. The iridescent green/blue feathers shine in sunlight, and the little twirl on the tail feather is rather endearing.

Envisioning the beauty of a dead Mallard is a different story – ew, gross; blood and guts and gore. It is hard for most of us to image the cellular structure of the insides of Mallard; indeed there are few reasons (or opportunities) to have a look at tissues under the microscope. I had an interesting opportunity to dissect a number of apparently healthy ducks with influenza A infections, and while I was supposed to be focused on the presence of influenza antigens, I couldn’t help but marvel at the beauty and intricacies of the inside of Mallards.

One of my favourite structures was the nasal concha – these spiral structures are found within the nasal cavities (ie inside the bill between the nares/nostrils and base of the skull), and have an important function in airflow, humidification, heating, and filtering of air inhaled through the nares. The walls of the nasal cavity, and the nasal concha, are lined with respiratory epithelium – tall rectangular cells, goblet cells (tall rectangular cells that secrete mucous), and cillia (or little “hairs” which move around the mucous or dirt). Below this layer, there are large mucous glands.

While learning about cellular structure and tissue anatomy, I was often captivated by sections that were “not normal”. Often these anomalies could be attributed to parasite infections. For example, one of the ducks had Capillaria (a nematode) eggs embedded in the epithelium of the oesophagus. The oesophagus is the tube that moves food down to the crop, and thus is highly muscular, contains innervations, and an abundance mucous glands for lubrication. This infection was probably unpleasant for the duck due to inflammation. Capillaria infection has not been recorded in wild Mallard oesophagus prior to this, but this is likely due to limited opportunity to examine tissues from wild birds.

A great misconception of scientists is that they take the beauty out of everything and try to analyze it. The contrasting reality is that most scientists find beauty in everything – from the study of charismatic megafauna, cellular structure, the colour and shape of bacterial colonies, to the sequences of genes and genomes. Though, from time to time it is important to remember to stop and smell the roses…

– Michelle Wille