Data from: Artificial light at night advances avian reproductive physiology

Artificial light at night is a rapidly increasing phenomenon and it is
presumed to have global implications. Light at night has been associated
with health problems in humans as a consequence of altered biological
rhythms. Effects on wild animals have been less investigated, but light at
night has often been assumed to affect seasonal cycles of urban dwellers.
Using light loggers attached to free-living European blackbirds (Turdus
merula), we first measured light intensity at night which forest and city
birds are subjected to in the wild. Then we used these measurements to
test for the effect of light at night on timing of reproductive
physiology. Captive city and forest blackbirds were exposed to either dark
nights or very low light intensities at night (0.3 lux). Birds exposed to
light at night developed their reproductive system up to one month
earlier, and also moulted earlier, than birds kept under dark nights.
Furthermore, city birds responded differently than forest individuals to
the light at night treatment, suggesting that urbanization can alter the
physiological phenotype of songbirds. Our results emphasize the impact of
human-induced lighting on the ecology of millions of animals living in
cities and call for an understanding of the fitness consequences of light
pollution.