OKINAWA, Japan, Nov. 4 (UPI) --Everything seems brighter in the tropics: the sky, the ocean, the houses, the birds. Think tropics and brightly feathered toucans and parrots come to mind. Why is that?

One obvious reason why people enjoy the existence of birds so much is their bright and varied colors. Humans — and most mammals — seem boring in comparison. But why are birds the colors that they are?

Tropical birds are well known for their colorful appearance: vibrantly colored macaws, parakeets and parrots are widely considered to be the quintessential birds of this region. The popularity of ...