Bird Ringing for Science and Conservation

Bird-transmitted diseases

When avian influenza virus of the H5N1 type started its way from southeast Asia westwards into Europe in 2005, the public interest of movements of wild birds reached a peak as has never been seen before. Newspapers and broadcasting stations asked for bird migration maps showing possible links between avian influenza outbreak regions and European countries. Although the complexity of bird movements made it difficult for ornithologists to give simple answers many insights into bird migration phenology could be conveyed to the public. The results presented were largely based on recovery data from bird ringing.

Not only mass media showed an increased interest in bird ringing results but also the European Commission and many national administrations also became aware of the value of bird ringing and even funded bird ringing projects and data analyses. This general interest in bird movements was driven by the assumption that wild birds – and especially waterfowl -are the main carriers of avian influenza and thus form the main risk for the introduction of the disease into countries and into poultry holdings. Again, largely based on bird ringing results, ornithologists were able to show that there are discrepancies between the movements of birds and the movement of H5N1avian influenza virus. This demonstrates the important fact that movements of wild birds are not the only – and probably not the most important – source of avian influenza outbreak risk. Later, virologists reconstructed pedigrees of the outbreaks by analysis of parts of the viruses’ genomes and supported this point of view. One famous example was a Whooper Swan which was among the first victims of the avian influenza outbreak on the German island of Rugen. This bird was marked with an individually numbered neck collar attached in its breeding grounds in Latvia and it was seen alive more than two weeks before the outbreak in the Rugen area. This bird, and some others with individual marks, told scientists a lot about transmission and epidemiology of avian influenza virus and helped to develop effective, but not excessive measures of defence against this disease.

More than half of the birds tested positive for H5N1 avian influenza virus in the 2006 European out-break were Mute Swans. Thanks to ringing programs, the movements of this partly migratory species in Europe is fairly well known.

Besides the spectacular H5N1 avian influenza outbreaks, scientists study many aspects of bird-transmitted diseases for two main reasons. Firstly, birds can be highly mobile and effective hosts and dispersers of diseases which may also effect plants, livestock, or humans. Besides Avian Influenza there is a wide range from West Nile Virus over Cercarial Dermatitis (“Swimmer’s Itch”) and Psittacosis (“Parrot Disease”) to humming bird-transmitted floral mites causing plant venereal diseases. Tracking of individuals, marked by bird rings, through space and time help us to understand the ways of spread and transmission of the disease. This helps to develop effective defences for the benefit of man, livestock and plants.

Eurasian Teal is one of the 17 species for which EURING has analysed recoveries in relation to High Pathogenicity Avian Influenza.

Secondly, the easy accessibility of birds, the large background knowledge that is already available about bird biology and the potential of a large community of amateur ornithologists gathering information make birds and their diseases ideal models for understanding the biology of hosts and parasites. With the help of thousands of amateur ornithologists watching House Finches in their gardens in the United States, scientists of the Cornell University (Ithaca, NY) were able to follow, over a whole continent, the dynamics of mycoplasmal conjunctivitis, a new eye disease infecting the finches. These observational data were completed by quantifying the effects of the disease on host demographic parameters via capture – mark – recapture modelling. By a similar approach – also requiring the individual ringing of birds – it is possible to investigate detection probabilities of disease carriers and assess disease prevalence. Both are important factors in understanding the co-evolution between a parasite (disease) and its host.