The number of starlings is in decline. But why? Data collected by volunteers, known as "citizen scientists", testifies to a drastic decline in the Danish starling population, but the data in itself cannot specifically explain the reason for this. A research collaboration between BirdLife Denmark and Aarhus University has addressed this question.

Henning Bjerg, employed at DCE in Kalø and BirdLife Denmark, has worked with citizen science for a long time.  Three years ago, he began a Ph.D. study to explore how to better utilise the large amounts of data provided by the collaboration with the volunteers. The study focused on how to improve the collaboration between the voluntary data collectors and the "real" scientists. This is done by combining the large amounts of data with data obtained from other areas. In this way, for example, the cause of the decline of starlings was found – mainly that their original habitats, the open land, which is used for grazing cows, had changed.

These new methods make it easier for Danish researchers to be up-to-date on the number of individuals of different bird species. According to EU legislation, Denmark is obliged to keep track of Danish animal life, and with the new methods it will be easier to find the causes of changes in the populations.

"The collaboration with AU has given us a high level of professionalism, which we can use to explain the decline in many species of birds" – Egon Østergaard, Chair of BirdLife.