de Jong M., van den Eertwegh L., Beskers R.E., de Vries P.P., Spoelstra K. & Visser M.E. (2018) Timing of avian breeding in an urbanised world. ARDEA 106 (1): 31-38

A large part of the world is urbanised, and the process of urbanisation is ongoing. This causes dramatic alterations of species’ habitat such as increased night light, sound levels and temperature, along with direct disturbance by human activity. We used eight years of citizen science data from ten common bird species breeding in nest boxes throughout The Netherlands to study the relationship between urbanisation and a key life history trait, timing of breeding. We used nightly light levels in the form of sky brightness and light emission as a proxy for urbanisation as the dramatic change of the night-time environment is a prominent effect of urbanisation. We expected birds to lay earlier in areas with more light at night, i.e. in more urbanised areas. We found, however, no relationship between light levels and seasonal timing in the ten species studied. A limitation of our study is that there was only limited data for the areas that were urbanised most (e.g. inside cities). Most nest box study areas are located in areas with a limited level of urbanisation, and hence with relatively low light levels of light at night. The lack of data on breeding birds in more urbanised environments, which is a rapidly expanding habitat for an increasing number of species worldwide, should be the focus of attention and citizen science would be highly suitable to also provide data for such areas.