More sun = evolution of brighter pigmentation in plants to catch or moderate light intake = natural selection of birds that can blend into that colorful vegetation. Would be my armchair hypothesis without reading the article.
inspiradia
I live in Denmark. One look out the window I could have told them. My theory would be that it has to do with vegetation losing its leaves during winter. It makes something orange WAY MORE visible.
Notyourfathersgeek
I wonder if this study took into account that some birds have pigments that are not in the human visible spectrum, and are therefore colorful.
Data-Minor
This wasn’t a theory, it was an untested hypothesis. A theory is expect to explain something. This was just a hypothesis about something that might be true
brainfreezereally
Or perhaps the sun is a variable nobody ever considers
MrSirDrDudeBro