The long-held theory, first suspected by Darwin and Humboldt, that tropical birds at the equator are more colourful than non-tropical birds has been proven analyzing 24,000 photos of birds. The new study suggests dietary differences, as well as the influence of their habitat, could play a key role

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