A new study helps reveal why tropical mountain birds occupy such narrow elevation ranges, a mystery that has puzzled scientists for centuries. While many assumed temperature was responsible for these limited distributions, the latest research suggests competition from other species plays a bigger role in shaping bird ranges.

The study, conducted by researchers at the University of British Columbia and the Cornell Lab of Ornithology, incorporated 4.4 million citizen science observations of 2,879 bird species around the world. The findings were published in Science on July 21.

"You have this incredible biodiversity in mountain ranges, especially in the tropics. From one vista point in the Andes, you can see a mountain slope that’s home to as many species as there are in the entirety of North America," said lead author Benjamin Freeman, a postdoctoral fellow at the University of British Columbia. "We wanted to know, how does that work?"

- Benjamin Hack

Read the full story at the Cornell Lab of Ornithology website.