https://phys.org/news/2018-10-mountain-birds-escalator-extinction-planet.html

"Once you move up as far as you can go, there's nowhere else left," said John W. Fitzpatrick, a study author and director of the Cornell Laboratory of Ornithology. "On this particular mountain, some ridgetop bird populations were literally wiped out."

It's not certain whether the birds shifted ranges because of temperature changes, or indirect impacts, such as shifts in the ranges of insects or seeds that they feed on.