In our research we capture and sample birds. Many, many birds – as in several thousands of birds over the years (2002 up to now). The reason we do this is to be able to connect individual birds with a test result. Is this duck infected or not with influenza? If, so what was its age, sex, and body condition at the time of sampling? This information helps us understand the disease dynamics in the mallard – virus system; how viruses affect the birds, and how birds affect virus evolution through their immune system.
We like to think that our meddling with the ducks is rather mild. The normal procedure includes the actual capture in the duck trap, the ringing and measuring of the bird, and the biological sampling procedure – normally a fecal or cloacal sample, but also feather samples or blood samples are sometimes taken. At times we have also used different loggers to collect data on movements, ranging from local stopover to migratory flights.
Given the questions we address in our research, we of course want the effects to be as small as possible. We haven’t formally investigated this ourselves. Fortunately, a recent publication, in the journal Ibis, used data from a similar influenza A virus surveillance scheme in France to investigate whether sampling incurs a cost or not. The authors focused on blood and cloacal swab sampling, and primarily analyzed survival and re-encounter rates.
They investigated four different duck species: Tufted duck, Pochard, Mallard and Teal. By comparing sets of ducks that only differed in which sampling type that had be taken (no sampling, cloacal sampling, blood sampling) the authors could use capture-mark-recapture analysis and logistic regression to test the hypothesis that sampling affected survival and re-encounter rates. To cut a long story short, they did not find any support for a negative effect on survival for any of the duck species tested due to sampling. Furthermore, re-encounter rates did not differ for three of the species, but did so for Teals (suggesting trap avoidance in this species).
This is a very good initiative, and I hope more researchers follow up their analysis. In my group, we have a lot of capture-mark-recapture data plus data on ring recoveries and we should be in a good position to look at these types of questions in the future, too. The results from the French paper corroborate my general gut feeling and some early preliminary analyses we conducted years ago. But it is good to get reliable, peer-reviewed data on this. Not the least given that surveillance schemes in Europe and North America have included sampling of hundred thousands of birds in the search for highly pathogenic H5N1 and H5N8.
Link to the article:
Guillemain, M., Champagnon, J., Gourlay-Larour, M-L., Cavallo, F., Brochet, A-L., Hars, J., Massez, G., George, T., Perroi, P-Y., Jestin, V. & Caizergues, A. 2015. Blood and cloacal swab sampling for avian influenza monitoring has no effect on survival rates of free-ranging ducks. Ibis 157: 743-753.